Parallel.For 方法

定义

执行 for 循环,其中可能会并行运行迭代。Executes a for loop in which iterations may run in parallel.

重载

For(Int32, Int32, Action<Int32,ParallelLoopState>)

执行 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop in which iterations may run in parallel and the state of the loop can be monitored and manipulated.

For(Int32, Int32, Action<Int32>)

执行 for 循环,其中可能会并行运行迭代。Executes a for loop in which iterations may run in parallel.

For(Int64, Int64, Action<Int64,ParallelLoopState>)

执行具有 64 位索引的 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop with 64-bit indexes in which iterations may run in parallel and the state of the loop can be monitored and manipulated.

For(Int64, Int64, Action<Int64>)

执行具有 64 位索引的 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop with 64-bit indexes in which iterations may run in parallel.

For(Int32, Int32, ParallelOptions, Action<Int32,ParallelLoopState>)

执行 for 循环,其中可能会并行运行迭代,而且可以配置循环选项,可以监视和操作循环的状态。Executes a for loop in which iterations may run in parallel, loop options can be configured, and the state of the loop can be monitored and manipulated.

For(Int32, Int32, ParallelOptions, Action<Int32>)

执行 for 循环,其中可能会并行运行迭代,而且可以配置循环选项。Executes a for loop in which iterations may run in parallel and loop options can be configured.

For(Int64, Int64, ParallelOptions, Action<Int64,ParallelLoopState>)

执行具有 64 位索引的 for 循环,其中可能会并行运行迭代,而且可以配置循环选项,可以监视和操作循环的状态。Executes a for loop with 64-bit indexes in which iterations may run in parallel, loop options can be configured, and the state of the loop can be monitored and manipulated.

For(Int64, Int64, ParallelOptions, Action<Int64>)

执行具有 64 位索引的 for 循环,其中可能会并行运行迭代,而且可以配置循环选项。Executes a for loop with 64-bit indexes in which iterations may run in parallel and loop options can be configured.

For<TLocal>(Int64, Int64, ParallelOptions, Func<TLocal>, Func<Int64,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有 64 位索引和线程本地数据的 for 循环,其中可能会并行运行迭代,而且可以配置循环选项,可以监视和操作循环的状态。Executes a for loop with 64-bit indexes and thread-local data in which iterations may run in parallel, loop options can be configured, and the state of the loop can be monitored and manipulated.

For<TLocal>(Int32, Int32, ParallelOptions, Func<TLocal>, Func<Int32,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有线程本地数据的 for 循环,其中可能会并行运行迭代,而且可以配置循环选项,可以监视和操作循环的状态。Executes a for loop with thread-local data in which iterations may run in parallel, loop options can be configured, and the state of the loop can be monitored and manipulated.

For<TLocal>(Int32, Int32, Func<TLocal>, Func<Int32,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有线程本地数据的 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop with thread-local data in which iterations may run in parallel, and the state of the loop can be monitored and manipulated.

For<TLocal>(Int64, Int64, Func<TLocal>, Func<Int64,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有 64 位索引和线程本地数据的 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop with 64-bit indexes and thread-local data in which iterations may run in parallel, and the state of the loop can be monitored and manipulated.

For(Int32, Int32, Action<Int32,ParallelLoopState>)

执行 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop in which iterations may run in parallel and the state of the loop can be monitored and manipulated.

public:
 static System::Threading::Tasks::ParallelLoopResult For(int fromInclusive, int toExclusive, Action<int, System::Threading::Tasks::ParallelLoopState ^> ^ body);
public static System.Threading.Tasks.ParallelLoopResult For (int fromInclusive, int toExclusive, Action<int,System.Threading.Tasks.ParallelLoopState> body);
static member For : int * int * Action<int, System.Threading.Tasks.ParallelLoopState> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For (fromInclusive As Integer, toExclusive As Integer, body As Action(Of Integer, ParallelLoopState)) As ParallelLoopResult

参数

fromInclusive
Int32

开始索引(含)。The start index, inclusive.

toExclusive
Int32

结束索引(不含)。The end index, exclusive.

body
Action<Int32,ParallelLoopState>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

body 参数为 nullThe body argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

示例

下面的示例并行执行最多100迭代的循环。The following example executes up to 100 iterations of a loop in parallel. 每个迭代都将暂停1到1000毫秒的随机间隔。Each iteration pauses for a random interval from 1 to 1,000 milliseconds. 随机生成的值确定调用 ParallelLoopState.Break 方法的循环迭代。A randomly generated value determines on which iteration of the loop the ParallelLoopState.Break method is called. 如示例的输出所示,在调用 ParallelLoopState.Break 方法后,索引大于 ParallelLoopState.LowestBreakIteration 属性值的任何迭代都将开始。As the output from the example shows, no iterations whose index is greater than the ParallelLoopState.LowestBreakIteration property value start after the call to the ParallelLoopState.Break method.

using System;
using System.Threading;
using System.Threading.Tasks;

public class Example
{
    public static void Main()
    {
        var rnd = new Random();
        int breakIndex = rnd.Next(1, 11);

        Console.WriteLine($"Will call Break at iteration {breakIndex}\n");

        var result = Parallel.For(1, 101, (i, state) => 
        {
            Console.WriteLine($"Beginning iteration {i}");
            int delay;
            lock (rnd)
                delay = rnd.Next(1, 1001);
            Thread.Sleep(delay);

            if (state.ShouldExitCurrentIteration)
            {
                if (state.LowestBreakIteration < i)
                    return;
            }

            if (i == breakIndex)
            {
                Console.WriteLine($"Break in iteration {i}");
                state.Break();
            }

            Console.WriteLine($"Completed iteration {i}");
        });

        if (result.LowestBreakIteration.HasValue)
            Console.WriteLine($"\nLowest Break Iteration: {result.LowestBreakIteration}");
        else
            Console.WriteLine($"\nNo lowest break iteration.");
    }
}
// The example displays output like the following:
//       Will call Break at iteration 8
//
//       Beginning iteration 1
//       Beginning iteration 13
//       Beginning iteration 97
//       Beginning iteration 25
//       Beginning iteration 49
//       Beginning iteration 37
//       Beginning iteration 85
//       Beginning iteration 73
//       Beginning iteration 61
//       Completed iteration 85
//       Beginning iteration 86
//       Completed iteration 61
//       Beginning iteration 62
//       Completed iteration 86
//       Beginning iteration 87
//       Completed iteration 37
//       Beginning iteration 38
//       Completed iteration 38
//       Beginning iteration 39
//       Completed iteration 25
//       Beginning iteration 26
//       Completed iteration 26
//       Beginning iteration 27
//       Completed iteration 73
//       Beginning iteration 74
//       Completed iteration 62
//       Beginning iteration 63
//       Completed iteration 39
//       Beginning iteration 40
//       Completed iteration 40
//       Beginning iteration 41
//       Completed iteration 13
//       Beginning iteration 14
//       Completed iteration 1
//       Beginning iteration 2
//       Completed iteration 97
//       Beginning iteration 98
//       Completed iteration 49
//       Beginning iteration 50
//       Completed iteration 87
//       Completed iteration 27
//       Beginning iteration 28
//       Completed iteration 50
//       Beginning iteration 51
//       Beginning iteration 88
//       Completed iteration 14
//       Beginning iteration 15
//       Completed iteration 15
//       Completed iteration 2
//       Beginning iteration 3
//       Beginning iteration 16
//       Completed iteration 63
//       Beginning iteration 64
//       Completed iteration 74
//       Beginning iteration 75
//       Completed iteration 41
//       Beginning iteration 42
//       Completed iteration 28
//       Beginning iteration 29
//       Completed iteration 29
//       Beginning iteration 30
//       Completed iteration 98
//       Beginning iteration 99
//       Completed iteration 64
//       Beginning iteration 65
//       Completed iteration 42
//       Beginning iteration 43
//       Completed iteration 88
//       Beginning iteration 89
//       Completed iteration 51
//       Beginning iteration 52
//       Completed iteration 16
//       Beginning iteration 17
//       Completed iteration 43
//       Beginning iteration 44
//       Completed iteration 44
//       Beginning iteration 45
//       Completed iteration 99
//       Beginning iteration 4
//       Completed iteration 3
//       Beginning iteration 8
//       Completed iteration 4
//       Beginning iteration 5
//       Completed iteration 52
//       Beginning iteration 53
//       Completed iteration 75
//       Beginning iteration 76
//       Completed iteration 76
//       Beginning iteration 77
//       Completed iteration 65
//       Beginning iteration 66
//       Completed iteration 5
//       Beginning iteration 6
//       Completed iteration 89
//       Beginning iteration 90
//       Completed iteration 30
//       Beginning iteration 31
//       Break in iteration 8
//       Completed iteration 8
//       Completed iteration 6
//       Beginning iteration 7
//       Completed iteration 7
//
//       Lowest Break Iteration: 8
Imports System.Threading
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      Dim rnd As New Random()
      Dim breakIndex As Integer = rnd.Next(1, 11)
      Dim lowest As New Nullable(Of Long)()

      Console.WriteLine("Will call Break at iteration {0}", breakIndex)
      Console.WriteLine()

      Dim result = Parallel.For(1, 101, Sub(i, state)
                                            Console.WriteLine("Beginning iteration {0}", i)
                                            Dim delay As Integer
                                            Monitor.Enter(rnd)
                                               delay = rnd.Next(1, 1001)
                                            Monitor.Exit(rnd)
                                            Thread.Sleep(delay)

                                            If state.ShouldExitCurrentIteration Then
                                               If state.LowestBreakIteration < i Then
                                                  Return
                                               End If
                                            End If

                                            If i = breakIndex Then
                                               Console.WriteLine("Break in iteration {0}", i)
                                               state.Break()
                                               If state.LowestBreakIteration.HasValue Then
                                                  If lowest < state.LowestBreakIteration Then
                                                     lowest = state.LowestBreakIteration
                                                  Else
                                                     lowest = state.LowestBreakIteration
                                                  End If
                                               End If
                                            End If

                                            Console.WriteLine("Completed iteration {0}", i)
                                       End Sub )
         Console.WriteLine()
         If lowest.HasValue Then
            Console.WriteLine("Lowest Break Iteration: {0}", lowest)
         Else
            Console.WriteLine("No lowest break iteration.")
         End If
   End Sub
End Module
' The example displays output like the following:
'       Will call Break at iteration 8
'
'       Beginning iteration 1
'       Beginning iteration 13
'       Beginning iteration 97
'       Beginning iteration 25
'       Beginning iteration 49
'       Beginning iteration 37
'       Beginning iteration 85
'       Beginning iteration 73
'       Beginning iteration 61
'       Completed iteration 85
'       Beginning iteration 86
'       Completed iteration 61
'       Beginning iteration 62
'       Completed iteration 86
'       Beginning iteration 87
'       Completed iteration 37
'       Beginning iteration 38
'       Completed iteration 38
'       Beginning iteration 39
'       Completed iteration 25
'       Beginning iteration 26
'       Completed iteration 26
'       Beginning iteration 27
'       Completed iteration 73
'       Beginning iteration 74
'       Completed iteration 62
'       Beginning iteration 63
'       Completed iteration 39
'       Beginning iteration 40
'       Completed iteration 40
'       Beginning iteration 41
'       Completed iteration 13
'       Beginning iteration 14
'       Completed iteration 1
'       Beginning iteration 2
'       Completed iteration 97
'       Beginning iteration 98
'       Completed iteration 49
'       Beginning iteration 50
'       Completed iteration 87
'       Completed iteration 27
'       Beginning iteration 28
'       Completed iteration 50
'       Beginning iteration 51
'       Beginning iteration 88
'       Completed iteration 14
'       Beginning iteration 15
'       Completed iteration 15
'       Completed iteration 2
'       Beginning iteration 3
'       Beginning iteration 16
'       Completed iteration 63
'       Beginning iteration 64
'       Completed iteration 74
'       Beginning iteration 75
'       Completed iteration 41
'       Beginning iteration 42
'       Completed iteration 28
'       Beginning iteration 29
'       Completed iteration 29
'       Beginning iteration 30
'       Completed iteration 98
'       Beginning iteration 99
'       Completed iteration 64
'       Beginning iteration 65
'       Completed iteration 42
'       Beginning iteration 43
'       Completed iteration 88
'       Beginning iteration 89
'       Completed iteration 51
'       Beginning iteration 52
'       Completed iteration 16
'       Beginning iteration 17
'       Completed iteration 43
'       Beginning iteration 44
'       Completed iteration 44
'       Beginning iteration 45
'       Completed iteration 99
'       Beginning iteration 4
'       Completed iteration 3
'       Beginning iteration 8
'       Completed iteration 4
'       Beginning iteration 5
'       Completed iteration 52
'       Beginning iteration 53
'       Completed iteration 75
'       Beginning iteration 76
'       Completed iteration 76
'       Beginning iteration 77
'       Completed iteration 65
'       Beginning iteration 66
'       Completed iteration 5
'       Beginning iteration 6
'       Completed iteration 89
'       Beginning iteration 90
'       Completed iteration 30
'       Beginning iteration 31
'       Break in iteration 8
'       Completed iteration 8
'       Completed iteration 6
'       Beginning iteration 7
'       Completed iteration 7
'
'       Lowest Break Iteration: 8

由于调用 ParallelLoopState.Break 方法时循环的迭代仍可能会执行,每次迭代都会调用 ParallelLoopState.ShouldExitCurrentIteration 属性来检查其他迭代是否已调用了 ParallelLoopState.Break 方法。Because iterations of the loop are still likely to be executing when the ParallelLoopState.Break method is called, each iteration calls the ParallelLoopState.ShouldExitCurrentIteration property to check whether another iteration has called the ParallelLoopState.Break method. 如果 true属性值,则迭代会检查 ParallelLoopState.LowestBreakIteration 属性的值,如果该值大于当前迭代的索引值,则会立即返回。If the property value is true, the iteration checks the value of the ParallelLoopState.LowestBreakIteration property and, if it is greater than the current iteration's index value, returns immediately.

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 提供两个参数:It is provided with two arguments:

  • 一个 Int32 值,该值表示迭代次数。An Int32 value that represents the iteration count.

  • 一个 ParallelLoopState 实例,可用于提前断开循环。A ParallelLoopState instance that can be used to break out of the loop prematurely. ParallelLoopState 的对象是由编译器创建的;它不能在用户代码中实例化。The ParallelLoopState object is created by the compiler; it cannot be instantiated in user code.

调用 Break 方法将通知 for 操作,即在当前的迭代之后无需执行迭代。Calling the Break method informs the for operation that iterations after the current one don't have to execute. 不过,如果所有迭代尚未执行,则仍必须执行当前的所有迭代。However, all iterations before the current one will still have to be executed if they haven't already.

因此,调用 Break 类似于一种语言(如C#)在传统的 for 循环内使用中断操作,但它不是完美的替代方法:例如,无法保证当前的迭代不会执行。Therefore, calling Break is similar to using a break operation within a conventional for loop in a language like C#, but it is not a perfect substitute: For example, there is no guarantee that iterations after the current one will definitely not execute.

如果在不需要当前迭代之前执行所有迭代,请使用 Stop 方法,而不是使用 BreakIf executing all iterations before the current one is not necessary, use the Stop method instead of using Break. 调用 Stop 会通知 for 循环,它可能会放弃所有剩余迭代,而不管它们是在当前迭代之前还是之后,因为所有必需的工作都已完成。Calling Stop informs the for loop that it may abandon all remaining iterations, regardless of whether they're before or after the current iteration, because all required work will have already been completed. 但是,与 Break一样,不能保证不会执行其他迭代。However, as with Break, there are no guarantees regarding which other iterations will not execute.

如果某个循环提前结束,则返回的 ParallelLoopResult 结构将包含有关循环完成的相关信息。If a loop is ended prematurely, the ParallelLoopResult structure that is returned will contain relevant information about the loop's completion.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, the method returns immediately without performing any iterations.

另请参阅

For(Int32, Int32, Action<Int32>)

执行 for 循环,其中可能会并行运行迭代。Executes a for loop in which iterations may run in parallel.

public:
 static System::Threading::Tasks::ParallelLoopResult For(int fromInclusive, int toExclusive, Action<int> ^ body);
public static System.Threading.Tasks.ParallelLoopResult For (int fromInclusive, int toExclusive, Action<int> body);
static member For : int * int * Action<int> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For (fromInclusive As Integer, toExclusive As Integer, body As Action(Of Integer)) As ParallelLoopResult

参数

fromInclusive
Int32

开始索引(含)。The start index, inclusive.

toExclusive
Int32

结束索引(不含)。The end index, exclusive.

body
Action<Int32>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

body 参数为 nullThe body argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

示例

下面的示例将 For 方法用于100调用的委托,该委托生成随机字节值并计算其总和。The following example uses the For method for 100 invocations of a delegate that generates random byte values and computes their sum.

using System;
using System.Threading.Tasks;

public class Example
{
   public static void Main()
   {
      ParallelLoopResult result = Parallel.For(0, 100, ctr => { Random rnd = new Random(ctr * 100000);
                                                                Byte[] bytes = new Byte[100];
                                                                rnd.NextBytes(bytes);
                                                                int sum = 0;
                                                                foreach(var byt in bytes)
                                                                    sum += byt;
                                                                Console.WriteLine("Iteration {0,2}: {1:N0}", ctr, sum);
                                                              });
      Console.WriteLine("Result: {0}", result.IsCompleted ? "Completed Normally" : 
                                                             String.Format("Completed to {0}", result.LowestBreakIteration));
   }
}
// The following is a portion of the output displayed by the example:
//       Iteration  0: 12,509
//       Iteration 50: 12,823
//       Iteration 51: 11,275
//       Iteration 52: 12,531
//       Iteration  1: 13,007
//       Iteration 53: 13,799
//       Iteration  4: 12,945
//       Iteration  2: 13,246
//       Iteration 54: 13,008
//       Iteration 55: 12,727
//       Iteration 56: 13,223
//       Iteration 57: 13,717
//       Iteration  5: 12,679
//       Iteration  3: 12,455
//       Iteration 58: 12,669
//       Iteration 59: 11,882
//       Iteration  6: 13,167
//       ...
//       Iteration 92: 12,275
//       Iteration 93: 13,282
//       Iteration 94: 12,745
//       Iteration 95: 11,957
//       Iteration 96: 12,455
//       Result: Completed Normally
Imports System.Threading.Tasks

Module Example
   Public Sub Main()
      Dim result As ParallelLoopResult = Parallel.For(0, 100, Sub(ctr)
                                                                 Dim rnd As New Random(ctr * 100000)
                                                                 Dim bytes(99) As Byte
                                                                 rnd.NextBytes(bytes)
                                                                 Dim sum As Integer
                                                                 For Each byt In bytes
                                                                    sum += byt
                                                                 Next
                                                                 Console.WriteLine("Iteration {0,2}: {1:N0}", ctr, sum)
                                                              End Sub)
      Console.WriteLine("Result: {0}", If(result.IsCompleted, "Completed Normally", 
                                                             String.Format("Completed to {0}", result.LowestBreakIteration)))
   End Sub
End Module
' The following is a portion of the output displayed by the example:
'       Iteration  0: 12,509
'       Iteration 50: 12,823
'       Iteration 51: 11,275
'       Iteration 52: 12,531
'       Iteration  1: 13,007
'       Iteration 53: 13,799
'       Iteration  4: 12,945
'       Iteration  2: 13,246
'       Iteration 54: 13,008
'       Iteration 55: 12,727
'       Iteration 56: 13,223
'       Iteration 57: 13,717
'       Iteration  5: 12,679
'       Iteration  3: 12,455
'       Iteration 58: 12,669
'       Iteration 59: 11,882
'       Iteration  6: 13,167
'       ...
'       Iteration 92: 12,275
'       Iteration 93: 13,282
'       Iteration 94: 12,745
'       Iteration 95: 11,957
'       Iteration 96: 12,455
'       Result: Completed Normally

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它以迭代次数(Int32)作为参数提供。It is provided with the iteration count (Int32) as a parameter.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, the method returns immediately without performing any iterations.

另请参阅

For(Int64, Int64, Action<Int64,ParallelLoopState>)

执行具有 64 位索引的 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop with 64-bit indexes in which iterations may run in parallel and the state of the loop can be monitored and manipulated.

public:
 static System::Threading::Tasks::ParallelLoopResult For(long fromInclusive, long toExclusive, Action<long, System::Threading::Tasks::ParallelLoopState ^> ^ body);
public static System.Threading.Tasks.ParallelLoopResult For (long fromInclusive, long toExclusive, Action<long,System.Threading.Tasks.ParallelLoopState> body);
static member For : int64 * int64 * Action<int64, System.Threading.Tasks.ParallelLoopState> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For (fromInclusive As Long, toExclusive As Long, body As Action(Of Long, ParallelLoopState)) As ParallelLoopResult

参数

fromInclusive
Int64

开始索引(含)。The start index, inclusive.

toExclusive
Int64

结束索引(不含)。The end index, exclusive.

body
Action<Int64,ParallelLoopState>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

返回

ParallelLoopResult

一个 ParallelLoopResult 结构,其中包含有关已完成的循环部分的信息。A ParallelLoopResult structure that contains information on what portion of the loop completed.

例外

body 参数为 nullThe body argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它附带了以下参数:迭代次数(Int64)和可用于提前中断循环的 ParallelLoopState 实例。It is provided with the following parameters: the iteration count (Int64), and a ParallelLoopState instance that may be used to break out of the loop prematurely.

调用 Break 方法将通知 for 操作,即在当前的迭代之后无需执行迭代,而在当前迭代之前的所有迭代都将执行。Calling the Break method informs the for operation that iterations after the current one don't have to be executed, but all iterations before the current one do.

因此,调用 Break 类似于一种语言(如C#)中的传统 for 循环内的中断操作,但它不是完美的替代方法:例如,无法保证当前的迭代不会执行。Therefore, calling Break is similar to using a break operation within a conventional for loop in a language like C#, but it is not a perfect substitute: For example, there is no guarantee that iterations after the current one will definitely not execute.

如果在不需要当前迭代之前执行所有迭代,请使用 Stop 方法,而不是使用 BreakIf executing all iterations before the current one is not necessary, use the Stop method instead of using Break. 调用 Stop 会通知 for 循环,它可能会放弃所有剩余迭代,而不管它们是在当前迭代之前还是之后,因为所有必需的工作都已完成。Calling Stop informs the for loop that it may abandon all remaining iterations, regardless of whether they're before or after the current iteration, because all required work will have already been completed. 但是,与 Break一样,不能保证不会执行其他迭代。However, as with Break, there are no guarantees regarding which other iterations will not execute.

如果某个循环提前结束,则返回的 ParallelLoopResult 结构将包含有关循环完成的相关信息。If a loop is ended prematurely, the ParallelLoopResult structure that is returned will contain relevant information about the loop's completion.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, then the method returns immediately without performing any iterations.

另请参阅

For(Int64, Int64, Action<Int64>)

执行具有 64 位索引的 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop with 64-bit indexes in which iterations may run in parallel.

public:
 static System::Threading::Tasks::ParallelLoopResult For(long fromInclusive, long toExclusive, Action<long> ^ body);
public static System.Threading.Tasks.ParallelLoopResult For (long fromInclusive, long toExclusive, Action<long> body);
static member For : int64 * int64 * Action<int64> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For (fromInclusive As Long, toExclusive As Long, body As Action(Of Long)) As ParallelLoopResult

参数

fromInclusive
Int64

开始索引(含)。The start index, inclusive.

toExclusive
Int64

结束索引(不含)。The end index, exclusive.

body
Action<Int64>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

body 参数为 nullThe body argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它以迭代次数(Int64)作为参数提供。It is provided with the iteration count (Int64) as a parameter.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, the method returns immediately without performing any iterations.

另请参阅

For(Int32, Int32, ParallelOptions, Action<Int32,ParallelLoopState>)

执行 for 循环,其中可能会并行运行迭代,而且可以配置循环选项,可以监视和操作循环的状态。Executes a for loop in which iterations may run in parallel, loop options can be configured, and the state of the loop can be monitored and manipulated.

public:
 static System::Threading::Tasks::ParallelLoopResult For(int fromInclusive, int toExclusive, System::Threading::Tasks::ParallelOptions ^ parallelOptions, Action<int, System::Threading::Tasks::ParallelLoopState ^> ^ body);
public static System.Threading.Tasks.ParallelLoopResult For (int fromInclusive, int toExclusive, System.Threading.Tasks.ParallelOptions parallelOptions, Action<int,System.Threading.Tasks.ParallelLoopState> body);
static member For : int * int * System.Threading.Tasks.ParallelOptions * Action<int, System.Threading.Tasks.ParallelLoopState> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For (fromInclusive As Integer, toExclusive As Integer, parallelOptions As ParallelOptions, body As Action(Of Integer, ParallelLoopState)) As ParallelLoopResult

参数

fromInclusive
Int32

开始索引(含)。The start index, inclusive.

toExclusive
Int32

结束索引(不含)。The end index, exclusive.

parallelOptions
ParallelOptions

一个对象,用于配置此操作的行为。An object that configures the behavior of this operation.

body
Action<Int32,ParallelLoopState>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

parallelOptions 取消的 CancellationToken 参数。The CancellationToken in the parallelOptions argument is canceled.

body 参数为 nullThe body argument is null.

- 或 --or- parallelOptions 参数为 nullThe parallelOptions argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

parallelOptions 中与 CancellationTokenSource 关联的 CancellationToken 已被释放。The CancellationTokenSource associated with the CancellationToken in the parallelOptions has been disposed.

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它附带了以下参数:迭代次数(Int32)和可用于提前中断循环的 ParallelLoopState 实例。It is provided with the following parameters: the iteration count (Int32), and a ParallelLoopState instance that may be used to break out of the loop prematurely.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, the method returns immediately without performing any iterations.

另请参阅

For(Int32, Int32, ParallelOptions, Action<Int32>)

执行 for 循环,其中可能会并行运行迭代,而且可以配置循环选项。Executes a for loop in which iterations may run in parallel and loop options can be configured.

public:
 static System::Threading::Tasks::ParallelLoopResult For(int fromInclusive, int toExclusive, System::Threading::Tasks::ParallelOptions ^ parallelOptions, Action<int> ^ body);
public static System.Threading.Tasks.ParallelLoopResult For (int fromInclusive, int toExclusive, System.Threading.Tasks.ParallelOptions parallelOptions, Action<int> body);
static member For : int * int * System.Threading.Tasks.ParallelOptions * Action<int> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For (fromInclusive As Integer, toExclusive As Integer, parallelOptions As ParallelOptions, body As Action(Of Integer)) As ParallelLoopResult

参数

fromInclusive
Int32

开始索引(含)。The start index, inclusive.

toExclusive
Int32

结束索引(不含)。The end index, exclusive.

parallelOptions
ParallelOptions

一个对象,用于配置此操作的行为。An object that configures the behavior of this operation.

body
Action<Int32>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

parallelOptions 取消的 CancellationToken 参数。The CancellationToken in the parallelOptions argument is canceled.

body 参数为 nullThe body argument is null.

- 或 --or- parallelOptions 参数为 nullThe parallelOptions argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

parallelOptions 中与 CancellationTokenSource 关联的 CancellationToken 已被释放。The CancellationTokenSource associated with the CancellationToken in the parallelOptions has been disposed.

示例

下面的示例演示如何取消并行循环:The following example shows how to cancel a parallel loop:


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

class ParallelForCancellation
{
    // Demonstrated features:
    //		CancellationTokenSource
    // 		Parallel.For()
    //		ParallelOptions
    //		ParallelLoopResult
    // Expected results:
    // 		An iteration for each argument value (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) is executed.
    //		The order of execution of the iterations is undefined.
    //		The iteration when i=2 cancels the loop.
    //		Some iterations may bail out or not start at all; because they are temporally executed in unpredictable order, 
    //          it is impossible to say which will start/complete and which won't.
    //		At the end, an OperationCancelledException is surfaced.
    // Documentation:
    //		http://msdn.microsoft.com/library/system.threading.cancellationtokensource(VS.100).aspx
    static void CancelDemo()
    {
        CancellationTokenSource cancellationSource = new CancellationTokenSource();
        ParallelOptions options = new ParallelOptions();
        options.CancellationToken = cancellationSource.Token;

        try
        {
            ParallelLoopResult loopResult = Parallel.For(
                    0,
                    10,
                    options,
                    (i, loopState) =>
                    {
                        Console.WriteLine("Start Thread={0}, i={1}", Thread.CurrentThread.ManagedThreadId, i);

                        // Simulate a cancellation of the loop when i=2
                        if (i == 2)
                        {
                            cancellationSource.Cancel();
                        }

                        // Simulates a long execution
                        for (int j = 0; j < 10; j++)
                        {
                            Thread.Sleep(1 * 200);

                            // check to see whether or not to continue
                            if (loopState.ShouldExitCurrentIteration) return;
                        }

                        Console.WriteLine("Finish Thread={0}, i={1}", Thread.CurrentThread.ManagedThreadId, i);
                    }
                );

            if (loopResult.IsCompleted)
            {
                Console.WriteLine("All iterations completed successfully. THIS WAS NOT EXPECTED.");
            }
        }
        // No exception is expected in this example, but if one is still thrown from a task,
        // it will be wrapped in AggregateException and propagated to the main thread.
        catch (AggregateException e)
        {
            Console.WriteLine("Parallel.For has thrown an AggregateException. THIS WAS NOT EXPECTED.\n{0}", e);
        }
        // Catching the cancellation exception
        catch (OperationCanceledException e)
        {
            Console.WriteLine("An iteration has triggered a cancellation. THIS WAS EXPECTED.\n{0}", e.ToString());
        }
        finally
        {
           cancellationSource.Dispose();
        }
    }
}
Imports System.Threading
Imports System.Threading.Tasks

Module LoopCancellation
    ' Demonstrated features:
    '   CancellationTokenSource
    '   Parallel.For()
    '   ParallelOptions
    '   ParallelLoopResult
    ' Expected results:
    '   An iteration for each argument value (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) is executed.
    '   The order of execution of the iterations is undefined.
    '   The iteration when i=2 cancels the loop.
    '   Some iterations may bail out or not start at all; because they are temporally executed in unpredictable order, 
    '      it is impossible to say which will start/complete and which won't.
    '   At the end, an OperationCancelledException is surfaced.
    ' Documentation:
    '   http://msdn.microsoft.com/library/system.threading.cancellationtokensource(VS.100).aspx
    Private Sub Main()
        Dim cancellationSource As New CancellationTokenSource()
        Dim options As New ParallelOptions()
        options.CancellationToken = cancellationSource.Token

        Try
            Dim loopResult As ParallelLoopResult = _
                Parallel.For(0, 10, options, Sub(i, loopState)
                                                 Console.WriteLine("Start Thread={0}, i={1}", Thread.CurrentThread.ManagedThreadId, i)

                                                 ' Simulate a cancellation of the loop when i=2
                                                 If i = 2 Then
                                                     cancellationSource.Cancel()
                                                 End If

                                                 ' Simulates a long execution
                                                 For j As Integer = 0 To 9
                                                     Thread.Sleep(1 * 200)

                                                     ' check to see whether or not to continue
                                                     If loopState.ShouldExitCurrentIteration Then
                                                         Exit Sub
                                                     End If
                                                 Next

                                                 Console.WriteLine("Finish Thread={0}, i={1}", Thread.CurrentThread.ManagedThreadId, i)
                                             End Sub)

            If loopResult.IsCompleted Then
                Console.WriteLine("All iterations completed successfully. THIS WAS NOT EXPECTED.")
            End If
        Catch e As AggregateException
            ' No exception is expected in this example, but if one is still thrown from a task,
            ' it will be wrapped in AggregateException and propagated to the main thread.
            Console.WriteLine("An action has thrown an AggregateException. THIS WAS NOT EXPECTED." & vbLf & "{0}", e)
        Catch e As OperationCanceledException
            ' Catching the cancellation exception
            Console.WriteLine("An iteration has triggered a cancellation. THIS WAS EXPECTED." & vbLf & "{0}", e)
        Finally
            cancellationSource.Dispose()
        End Try
    End Sub
End Module

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它以迭代次数(Int32)作为参数提供。It is provided with the iteration count (Int32) as a parameter.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, then the method returns immediately without performing any iterations.

另请参阅

For(Int64, Int64, ParallelOptions, Action<Int64,ParallelLoopState>)

执行具有 64 位索引的 for 循环,其中可能会并行运行迭代,而且可以配置循环选项,可以监视和操作循环的状态。Executes a for loop with 64-bit indexes in which iterations may run in parallel, loop options can be configured, and the state of the loop can be monitored and manipulated.

public:
 static System::Threading::Tasks::ParallelLoopResult For(long fromInclusive, long toExclusive, System::Threading::Tasks::ParallelOptions ^ parallelOptions, Action<long, System::Threading::Tasks::ParallelLoopState ^> ^ body);
public static System.Threading.Tasks.ParallelLoopResult For (long fromInclusive, long toExclusive, System.Threading.Tasks.ParallelOptions parallelOptions, Action<long,System.Threading.Tasks.ParallelLoopState> body);
static member For : int64 * int64 * System.Threading.Tasks.ParallelOptions * Action<int64, System.Threading.Tasks.ParallelLoopState> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For (fromInclusive As Long, toExclusive As Long, parallelOptions As ParallelOptions, body As Action(Of Long, ParallelLoopState)) As ParallelLoopResult

参数

fromInclusive
Int64

开始索引(含)。The start index, inclusive.

toExclusive
Int64

结束索引(不含)。The end index, exclusive.

parallelOptions
ParallelOptions

一个对象,用于配置此操作的行为。An object that configures the behavior of this operation.

body
Action<Int64,ParallelLoopState>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

parallelOptions 取消的 CancellationToken 参数。The CancellationToken in the parallelOptions argument is canceled.

body 参数为 nullThe body argument is null.

- 或 --or- parallelOptions 参数为 nullThe parallelOptions argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

parallelOptions 中与 CancellationTokenSource 关联的 CancellationToken 已被释放。The CancellationTokenSource associated with the CancellationToken in the parallelOptions has been disposed.

示例

下面的示例演示如何将 Parallel.For 方法与 ParallelOptions 对象结合使用:The following example shows how to use the Parallel.For method with a ParallelOptions object:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

class ParallelOptionsDemo
{
    // Demonstrated features:
    // 		Parallel.For()
    //		ParallelOptions
    // Expected results:
    // 		An iteration for each argument value (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) is executed.
    //		The order of execution of the iterations is undefined.
    //		Verify that no more than two threads have been used for the iterations.
    // Documentation:
    //		http://msdn.microsoft.com/library/system.threading.tasks.parallel.for(VS.100).aspx
    static void Main()
    {
        ParallelOptions options = new ParallelOptions();
        options.MaxDegreeOfParallelism = 2; // -1 is for unlimited. 1 is for sequential.

        try
        {
            Parallel.For(
                    0,
                    9,
                    options,
                    (i) =>
                    {
                        Console.WriteLine("Thread={0}, i={1}", Thread.CurrentThread.ManagedThreadId, i);
                    }
                );
        }
        // No exception is expected in this example, but if one is still thrown from a task,
        // it will be wrapped in AggregateException and propagated to the main thread.
        catch (AggregateException e)
        {
            Console.WriteLine("Parallel.For has thrown the following (unexpected) exception:\n{0}", e);
        }
    }
}


Imports System.Threading
Imports System.Threading.Tasks


Module ParallelForDemo

    ' Demonstrated features:
    '   Parallel.For()
    '   ParallelOptions
    ' Expected results:
    '   An iteration for each argument value (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) is executed.
    '   The order of execution of the iterations is undefined.
    '   Verify that no more than two threads have been used for the iterations.
    ' Documentation:
    '   http://msdn.microsoft.com/library/system.threading.tasks.parallel.for(VS.100).aspx
    Sub Main()
        Dim options As New ParallelOptions()
        options.MaxDegreeOfParallelism = 2 ' -1 is for unlimited. 1 is for sequential.
        Try
            Parallel.For(0, 9, options, Sub(i)
                                            Console.WriteLine("Thread={0}, i={1}", Thread.CurrentThread.ManagedThreadId, i)

                                        End Sub)
        Catch e As AggregateException
            ' No exception is expected in this example, but if one is still thrown from a task,
            ' it will be wrapped in AggregateException and propagated to the main thread.
            Console.WriteLine("Parallel.For has thrown the following (unexpected) exception:" & vbLf & "{0}", e)
        End Try
    End Sub

End Module

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它附带了以下参数:迭代次数(Int64)和可用于提前中断循环的 ParallelLoopState 实例。It is provided with the following parameters: the iteration count (Int64), and a ParallelLoopState instance that may be used to break out of the loop prematurely.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, the method returns immediately without performing any iterations.

另请参阅

For(Int64, Int64, ParallelOptions, Action<Int64>)

执行具有 64 位索引的 for 循环,其中可能会并行运行迭代,而且可以配置循环选项。Executes a for loop with 64-bit indexes in which iterations may run in parallel and loop options can be configured.

public:
 static System::Threading::Tasks::ParallelLoopResult For(long fromInclusive, long toExclusive, System::Threading::Tasks::ParallelOptions ^ parallelOptions, Action<long> ^ body);
public static System.Threading.Tasks.ParallelLoopResult For (long fromInclusive, long toExclusive, System.Threading.Tasks.ParallelOptions parallelOptions, Action<long> body);
static member For : int64 * int64 * System.Threading.Tasks.ParallelOptions * Action<int64> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For (fromInclusive As Long, toExclusive As Long, parallelOptions As ParallelOptions, body As Action(Of Long)) As ParallelLoopResult

参数

fromInclusive
Int64

开始索引(含)。The start index, inclusive.

toExclusive
Int64

结束索引(不含)。The end index, exclusive.

parallelOptions
ParallelOptions

一个对象,用于配置此操作的行为。An object that configures the behavior of this operation.

body
Action<Int64>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

parallelOptions 取消的 CancellationToken 参数。The CancellationToken in the parallelOptions argument is canceled.

body 参数为 nullThe body argument is null.

- 或 --or- parallelOptions 参数为 nullThe parallelOptions argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

parallelOptions 中与 CancellationTokenSource 关联的 CancellationToken 已被释放。The CancellationTokenSource associated with the CancellationToken in the parallelOptions has been disposed.

示例

下面的示例演示如何使用 ParallelOptions 来指定自定义任务计划程序:The following example shows how to use ParallelOptions to specify a custom task scheduler:

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

class ParallelSchedulerDemo2
{
        // Demonstrated features:
        //		TaskScheduler
        //      BlockingCollection
        // 		Parallel.For()
        //		ParallelOptions
        // Expected results:
        // 		An iteration for each argument value (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) is executed.
        //		The TwoThreadTaskScheduler employs 2 threads on which iterations may be executed in a random order.
        //		Thus a scheduler thread may execute multiple iterations.
        // Documentation:
        //		http://msdn.microsoft.com/library/system.threading.tasks.taskscheduler(VS.100).aspx
        //		http://msdn.microsoft.com/library/dd997413(VS.100).aspx
        // More information:
        //		http://blogs.msdn.com/pfxteam/archive/2009/09/22/9898090.aspx
        static void Main()
        {
            ParallelOptions options = new ParallelOptions();

            // Construct and associate a custom task scheduler
            options.TaskScheduler = new TwoThreadTaskScheduler();

            try
            {
                Parallel.For(
                        0,
                        10,
                        options,
                        (i, localState) =>
                        {
                            Console.WriteLine("i={0}, Task={1}, Thread={2}", i, Task.CurrentId, Thread.CurrentThread.ManagedThreadId);
                        }
                    );
            }
            // No exception is expected in this example, but if one is still thrown from a task,
            // it will be wrapped in AggregateException and propagated to the main thread.
            catch (AggregateException e)
            {
                Console.WriteLine("An iteration has thrown an exception. THIS WAS NOT EXPECTED.\n{0}", e);
            }
        }

        // This scheduler schedules all tasks on (at most) two threads
        sealed class TwoThreadTaskScheduler : TaskScheduler, IDisposable
        {
            // The runtime decides how many tasks to create for the given set of iterations, loop options, and scheduler's max concurrency level.
            // Tasks will be queued in this collection
            private BlockingCollection<Task> _tasks = new BlockingCollection<Task>();

            // Maintain an array of threads. (Feel free to bump up _n.)
            private readonly int _n = 2;
            private Thread[] _threads;

            public TwoThreadTaskScheduler()
            {
                _threads = new Thread[_n];

                // Create unstarted threads based on the same inline delegate
                for (int i = 0; i < _n; i++)
                {
                    _threads[i] = new Thread(() =>
                    {
                        // The following loop blocks until items become available in the blocking collection.
                        // Then one thread is unblocked to consume that item.
                        foreach (var task in _tasks.GetConsumingEnumerable())
                        {
                            TryExecuteTask(task);
                        }
                    });

                    // Start each thread
                    _threads[i].IsBackground = true;
                    _threads[i].Start();
                }
            }

            // This method is invoked by the runtime to schedule a task
            protected override void QueueTask(Task task)
            {
                _tasks.Add(task);
            }

            // The runtime will probe if a task can be executed in the current thread.
            // By returning false, we direct all tasks to be queued up.
            protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
            {
                return false;
            }

            public override int MaximumConcurrencyLevel { get { return _n; } }

            protected override IEnumerable<Task> GetScheduledTasks()
            {
                return _tasks.ToArray();
            }

            // Dispose is not thread-safe with other members.
            // It may only be used when no more tasks will be queued
            // to the scheduler.  This implementation will block
            // until all previously queued tasks have completed.
            public void Dispose()
            {
                if (_threads != null)
                {
                    _tasks.CompleteAdding();

                    for (int i = 0; i < _n; i++)
                    {
                        _threads[i].Join();
                        _threads[i] = null;
                    }
                    _threads = null;
                    _tasks.Dispose();
                    _tasks = null;
                }
            }
    }
}
Imports System.Collections.Concurrent
Imports System.Threading
Imports System.Threading.Tasks

Module SchedulerDemo
    ' Demonstrated features:
    '   TaskScheduler
    '   BlockingCollection
    '   Parallel.For()
    '   ParallelOptions
    ' Expected results:
    '   An iteration for each argument value (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) is executed.
    '   The TwoThreadTaskScheduler employs 2 threads on which iterations may be executed in a random order.
    '   A task is internally created for each thread of the task scheduler (plus an aditional internal task).
    '	Thus a scheduler thread may execute multiple iterations.
    ' Documentation:
    '   http://msdn.microsoft.com/library/system.threading.tasks.taskscheduler(VS.100).aspx
    '   http://msdn.microsoft.com/library/dd997413(VS.100).aspx
    ' More information:
    '   http://blogs.msdn.com/pfxteam/archive/2009/09/22/9898090.aspx
    Sub Main()
        Dim options As New ParallelOptions()

        ' Construct and associate a custom task scheduler
        options.TaskScheduler = New TwoThreadTaskScheduler()

        Try
            Parallel.For(0, 10, options, Sub(i, localState)
                                             Console.WriteLine("i={0}, Task={1}, Thread={2}", i, Task.CurrentId, Thread.CurrentThread.ManagedThreadId)

                                         End Sub)
        Catch e As AggregateException
            ' No exception is expected in this example, but if one is still thrown from a task,
            ' it will be wrapped in AggregateException and propagated to the main thread.
            Console.WriteLine("An iteration has thrown an exception. THIS WAS NOT EXPECTED." & vbLf & "{0}", e)
        End Try
    End Sub

    ' This scheduler schedules all tasks on (at most) two threads
    Private NotInheritable Class TwoThreadTaskScheduler
        Inherits TaskScheduler
        Implements IDisposable
        ' The runtime decides how many tasks to create for the given set of iterations, loop options, and scheduler's max concurrency level.
        ' Tasks will be queued in this collection
        Private _tasks As New BlockingCollection(Of Task)()

        ' Maintain an array of threads. (Feel free to bump up _n.)
        Private ReadOnly _n As Integer = 2
        Private _threads As Thread()

        Public Sub New()
            _threads = New Thread(_n - 1) {}

            ' Create unstarted threads based on the same inline delegate
            For i As Integer = 0 To _n - 1
                _threads(i) = New Thread(Sub()
                                             ' The following loop blocks until items become available in the blocking collection.
                                             ' Then one thread is unblocked to consume that item.
                                             For Each task In _tasks.GetConsumingEnumerable()
                                                 TryExecuteTask(task)
                                             Next
                                         End Sub)

                ' Start each thread
                _threads(i).IsBackground = True
                _threads(i).Start()
            Next
        End Sub

        ' This method is invoked by the runtime to schedule a task
        Protected Overloads Overrides Sub QueueTask(ByVal task As Task)
            _tasks.Add(task)
        End Sub

        ' The runtime will probe if a task can be executed in the current thread.
        ' By returning false, we direct all tasks to be queued up.
        Protected Overloads Overrides Function TryExecuteTaskInline(ByVal task As Task, ByVal taskWasPreviouslyQueued As Boolean) As Boolean
            Return False
        End Function

        Public Overloads Overrides ReadOnly Property MaximumConcurrencyLevel() As Integer
            Get
                Return _n
            End Get
        End Property

        Protected Overloads Overrides Function GetScheduledTasks() As IEnumerable(Of Task)
            Return _tasks.ToArray()
        End Function

        ' Dispose is not thread-safe with other members.
        ' It may only be used when no more tasks will be queued
        ' to the scheduler. This implementation will block
        ' until all previously queued tasks have completed.
        Public Sub Dispose() Implements IDisposable.Dispose
            If _threads IsNot Nothing Then
                _tasks.CompleteAdding()

                For i As Integer = 0 To _n - 1
                    _threads(i).Join()
                    _threads(i) = Nothing
                Next
                _threads = Nothing
                _tasks.Dispose()
                _tasks = Nothing
            End If
        End Sub
    End Class

End Module

注解

支持64位索引。Supports 64-bit indexes. 对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它以迭代次数(Int64)作为参数提供。It is provided with the iteration count (Int64) as a parameter.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, then the method returns immediately without performing any iterations.

另请参阅

For<TLocal>(Int64, Int64, ParallelOptions, Func<TLocal>, Func<Int64,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有 64 位索引和线程本地数据的 for 循环,其中可能会并行运行迭代,而且可以配置循环选项,可以监视和操作循环的状态。Executes a for loop with 64-bit indexes and thread-local data in which iterations may run in parallel, loop options can be configured, and the state of the loop can be monitored and manipulated.

public:
generic <typename TLocal>
 static System::Threading::Tasks::ParallelLoopResult For(long fromInclusive, long toExclusive, System::Threading::Tasks::ParallelOptions ^ parallelOptions, Func<TLocal> ^ localInit, Func<long, System::Threading::Tasks::ParallelLoopState ^, TLocal, TLocal> ^ body, Action<TLocal> ^ localFinally);
public static System.Threading.Tasks.ParallelLoopResult For<TLocal> (long fromInclusive, long toExclusive, System.Threading.Tasks.ParallelOptions parallelOptions, Func<TLocal> localInit, Func<long,System.Threading.Tasks.ParallelLoopState,TLocal,TLocal> body, Action<TLocal> localFinally);
static member For : int64 * int64 * System.Threading.Tasks.ParallelOptions * Func<'Local> * Func<int64, System.Threading.Tasks.ParallelLoopState, 'Local, 'Local> * Action<'Local> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For(Of TLocal) (fromInclusive As Long, toExclusive As Long, parallelOptions As ParallelOptions, localInit As Func(Of TLocal), body As Func(Of Long, ParallelLoopState, TLocal, TLocal), localFinally As Action(Of TLocal)) As ParallelLoopResult

类型参数

TLocal

线程本地数据的类型。The type of the thread-local data.

参数

fromInclusive
Int64

开始索引(含)。The start index, inclusive.

toExclusive
Int64

结束索引(不含)。The end index, exclusive.

parallelOptions
ParallelOptions

一个对象,用于配置此操作的行为。An object that configures the behavior of this operation.

localInit
Func<TLocal>

用于返回每个线程的本地数据的初始状态的函数委托。The function delegate that returns the initial state of the local data for each thread.

body
Func<Int64,ParallelLoopState,TLocal,TLocal>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

localFinally
Action<TLocal>

用于对每个线程的本地状态执行一个最终操作的委托。The delegate that performs a final action on the local state of each thread.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

body 参数为 nullThe body argument is null.

- 或 --or- localInit 参数为 nullThe localInit argument is null.

- 或 --or- localFinally 参数为 nullThe localFinally argument is null.

- 或 --or- parallelOptions 参数为 nullThe parallelOptions argument is null.

parallelOptions 取消的 CancellationToken 参数。The CancellationToken in the parallelOptions argument is canceled.

parallelOptions 中与 CancellationTokenSource 关联的 CancellationToken 已被释放。The CancellationTokenSource associated with the CancellationToken in the parallelOptions has been disposed.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它提供有以下参数:迭代数(Int64)、可能用于提前跳出循环的 ParallelLoopState 实例,以及可能在同一线程上执行的迭代之间共享的某些本地状态。It is provided with the following parameters: the iteration count (Int64), a ParallelLoopState instance that may be used to break out of the loop prematurely, and some local state that may be shared amongst iterations that execute on the same thread.

为参与循环执行的每个线程调用一次 localInit 委托,并返回每个线程的初始本地状态。The localInit delegate is invoked once for each thread that participates in the loop's execution and returns the initial local state for each of those threads. 这些初始状态将传递到每个线程上的第一个 body 调用。These initial states are passed to the first body invocations on each thread. 然后,每个后续的主体调用都将返回一个可能修改的状态值,并将其传递给下一个主体调用。Then, every subsequent body invocation returns a possibly modified state value that is passed to the next body invocation. 最后,每个线程上的最后一个主体调用返回传递给 localFinally 委托的状态值。Finally, the last body invocation on each thread returns a state value that is passed to the localFinally delegate. 每个线程调用 localFinally 委托,以便对每个线程的本地状态执行最后一个操作。The localFinally delegate is invoked once per thread to perform a final action on each thread's local state. 可以在多个线程上同时调用此委托;因此,必须同步对任何共享变量的访问。This delegate might be invoked concurrently on multiple threads; therefore, you must synchronize access to any shared variables.

当现有任务完成并被新任务替换时,Parallel.For 方法可能使用比线程多的任务,而不是使用线程。The Parallel.For method may use more tasks than threads over the lifetime of its execution, as existing tasks complete and are replaced by new tasks. 这为底层 TaskScheduler 对象提供了添加、更改或删除服务循环的线程的机会。This gives the underlying TaskScheduler object the chance to add, change, or remove threads that service the loop.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, then the method returns immediately without performing any iterations.

另请参阅

For<TLocal>(Int32, Int32, ParallelOptions, Func<TLocal>, Func<Int32,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有线程本地数据的 for 循环,其中可能会并行运行迭代,而且可以配置循环选项,可以监视和操作循环的状态。Executes a for loop with thread-local data in which iterations may run in parallel, loop options can be configured, and the state of the loop can be monitored and manipulated.

public:
generic <typename TLocal>
 static System::Threading::Tasks::ParallelLoopResult For(int fromInclusive, int toExclusive, System::Threading::Tasks::ParallelOptions ^ parallelOptions, Func<TLocal> ^ localInit, Func<int, System::Threading::Tasks::ParallelLoopState ^, TLocal, TLocal> ^ body, Action<TLocal> ^ localFinally);
public static System.Threading.Tasks.ParallelLoopResult For<TLocal> (int fromInclusive, int toExclusive, System.Threading.Tasks.ParallelOptions parallelOptions, Func<TLocal> localInit, Func<int,System.Threading.Tasks.ParallelLoopState,TLocal,TLocal> body, Action<TLocal> localFinally);
static member For : int * int * System.Threading.Tasks.ParallelOptions * Func<'Local> * Func<int, System.Threading.Tasks.ParallelLoopState, 'Local, 'Local> * Action<'Local> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For(Of TLocal) (fromInclusive As Integer, toExclusive As Integer, parallelOptions As ParallelOptions, localInit As Func(Of TLocal), body As Func(Of Integer, ParallelLoopState, TLocal, TLocal), localFinally As Action(Of TLocal)) As ParallelLoopResult

类型参数

TLocal

线程本地数据的类型。The type of the thread-local data.

参数

fromInclusive
Int32

开始索引(含)。The start index, inclusive.

toExclusive
Int32

结束索引(不含)。The end index, exclusive.

parallelOptions
ParallelOptions

一个对象,用于配置此操作的行为。An object that configures the behavior of this operation.

localInit
Func<TLocal>

用于返回每个任务的本地数据的初始状态的函数委托。The function delegate that returns the initial state of the local data for each task.

body
Func<Int32,ParallelLoopState,TLocal,TLocal>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

localFinally
Action<TLocal>

用于对每个任务的本地状态执行一个最终操作的委托。The delegate that performs a final action on the local state of each task.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

body 参数为 nullThe body argument is null.

- 或 --or- localInit 参数为 nullThe localInit argument is null.

- 或 --or- localFinally 参数为 nullThe localFinally argument is null.

- 或 --or- parallelOptions 参数为 nullThe parallelOptions argument is null.

parallelOptions 取消的 CancellationToken 参数。The CancellationToken in the parallelOptions argument is canceled.

parallelOptions 中与 CancellationTokenSource 关联的 CancellationToken 已被释放。The CancellationTokenSource associated with the CancellationToken in the parallelOptions has been disposed.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

示例

下面的示例使用线程本地变量来计算许多长运算的结果之和。The following example uses thread-local variables to compute the sum of the results of many lengthy operations. 此示例将并行度限制为四。This example limits the degree of parallelism to four.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

class ThreadLocalForWithOptions
{
   // The number of parallel iterations to perform.
   const int N = 1000000;

   static void Main()
   {
      // The result of all thread-local computations.
      int result = 0;

      // This example limits the degree of parallelism to four.
      // You might limit the degree of parallelism when your algorithm
      // does not scale beyond a certain number of cores or when you 
      // enforce a particular quality of service in your application.

      Parallel.For(0, N, new ParallelOptions { MaxDegreeOfParallelism = 4 },
         // Initialize the local states
         () => 0,
         // Accumulate the thread-local computations in the loop body
         (i, loop, localState) =>
         {
            return localState + Compute(i);
         },
         // Combine all local states
         localState => Interlocked.Add(ref result, localState)
      );

      // Print the actual and expected results.
      Console.WriteLine("Actual result: {0}. Expected 1000000.", result);
   }

   // Simulates a lengthy operation.
   private static int Compute(int n)
   {
      for (int i = 0; i < 10000; i++) ;
      return 1;
   }
}
Imports System.Threading
Imports System.Threading.Tasks

Module ThreadLocalForWithOptions

   ' The number of parallel iterations to perform.
   Const N As Integer = 1000000

   Sub Main()
      ' The result of all thread-local computations.
      Dim result As Integer = 0

      ' This example limits the degree of parallelism to four.
      ' You might limit the degree of parallelism when your algorithm
      ' does not scale beyond a certain number of cores or when you 
      ' enforce a particular quality of service in your application.

      Parallel.For(0, N, New ParallelOptions With {.MaxDegreeOfParallelism = 4},
         Function()
            ' Initialize the local states 
            Return 0
         End Function,
         Function(i, loopState, localState)
            ' Accumulate the thread-local computations in the loop body
            Return localState + Compute(i)
         End Function,
         Sub(localState)
            ' Combine all local states
            Interlocked.Add(result, localState)
         End Sub
      )

      ' Print the actual and expected results.
      Console.WriteLine("Actual result: {0}. Expected 1000000.", result)
   End Sub

   ' Simulates a lengthy operation.
   Function Compute(ByVal n As Integer) As Integer
      For i As Integer = 0 To 10000
      Next
      Return 1
   End Function
End Module

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它提供有以下参数:迭代数(Int32)、可能用于提前跳出循环的 ParallelLoopState 实例,以及可能在同一任务上执行的迭代之间共享的某些本地状态。It is provided with the following parameters: the iteration count (Int32), a ParallelLoopState instance that may be used to break out of the loop prematurely, and some local state that may be shared amongst iterations that execute on the same task.

对于参与循环执行的每个任务调用一次 localInit 委托,并返回每个任务的初始本地状态。The localInit delegate is invoked once for each task that participates in the loop's execution and returns the initial local state for each of those tasks. 这些初始状态将传递给每个任务上的第一个 body 调用。These initial states are passed to the first body invocations on each task. 然后,每个后续的主体调用都将返回一个可能修改的状态值,并将其传递给下一个主体调用。Then, every subsequent body invocation returns a possibly modified state value that is passed to the next body invocation. 最后,每个任务的最后一个主体调用返回一个传递给 localFinally 委托的状态值。Finally, the last body invocation on each task returns a state value that is passed to the localFinally delegate. 每个任务调用一次 localFinally 委托,以便对每个任务的本地状态执行最后一个操作。The localFinally delegate is invoked once per task to perform a final action on each task's local state. 可以在多个线程上同时调用此委托;因此,必须同步对任何共享变量的访问。This delegate might be invoked concurrently on multiple threads; therefore, you must synchronize access to any shared variables.

当现有任务完成并被新任务替换时,Parallel.For 方法可能使用比线程多的任务,而不是使用线程。The Parallel.For method may use more tasks than threads over the lifetime of its execution, as existing tasks complete and are replaced by new tasks. 这为底层 TaskScheduler 对象提供了添加、更改或删除服务循环的线程的机会。This gives the underlying TaskScheduler object the chance to add, change, or remove threads that service the loop.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, then the method returns immediately without performing any iterations.

另请参阅

For<TLocal>(Int32, Int32, Func<TLocal>, Func<Int32,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有线程本地数据的 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop with thread-local data in which iterations may run in parallel, and the state of the loop can be monitored and manipulated.

public:
generic <typename TLocal>
 static System::Threading::Tasks::ParallelLoopResult For(int fromInclusive, int toExclusive, Func<TLocal> ^ localInit, Func<int, System::Threading::Tasks::ParallelLoopState ^, TLocal, TLocal> ^ body, Action<TLocal> ^ localFinally);
public static System.Threading.Tasks.ParallelLoopResult For<TLocal> (int fromInclusive, int toExclusive, Func<TLocal> localInit, Func<int,System.Threading.Tasks.ParallelLoopState,TLocal,TLocal> body, Action<TLocal> localFinally);
static member For : int * int * Func<'Local> * Func<int, System.Threading.Tasks.ParallelLoopState, 'Local, 'Local> * Action<'Local> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For(Of TLocal) (fromInclusive As Integer, toExclusive As Integer, localInit As Func(Of TLocal), body As Func(Of Integer, ParallelLoopState, TLocal, TLocal), localFinally As Action(Of TLocal)) As ParallelLoopResult

类型参数

TLocal

线程本地数据的类型。The type of the thread-local data.

参数

fromInclusive
Int32

开始索引(含)。The start index, inclusive.

toExclusive
Int32

结束索引(不含)。The end index, exclusive.

localInit
Func<TLocal>

用于返回每个任务的本地数据的初始状态的函数委托。The function delegate that returns the initial state of the local data for each task.

body
Func<Int32,ParallelLoopState,TLocal,TLocal>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

localFinally
Action<TLocal>

用于对每个任务的本地状态执行一个最终操作的委托。The delegate that performs a final action on the local state of each task.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

body 参数为 nullThe body argument is null.

- 或 --or- localInit 参数为 nullThe localInit argument is null.

- 或 --or- localFinally 参数为 nullThe localFinally argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它提供有以下参数:迭代数(Int32)、可能用于提前跳出循环的 ParallelLoopState 实例,以及可能在同一线程上执行的迭代之间共享的某些本地状态。It is provided with the following parameters: the iteration count (Int32), a ParallelLoopState instance that may be used to break out of the loop prematurely, and some local state that may be shared amongst iterations that execute on the same thread.

对于参与循环执行的每个任务调用一次 localInit 委托,并返回每个任务的初始本地状态。The localInit delegate is invoked once for each task that participates in the loop's execution and returns the initial local state for each of those tasks. 这些初始状态将传递给每个任务上的第一个 body 调用。These initial states are passed to the first body invocations on each task. 然后,每个后续的主体调用都将返回一个可能修改的状态值,并将其传递给下一个主体调用。Then, every subsequent body invocation returns a possibly modified state value that is passed to the next body invocation. 最后,每个任务的最后一个主体调用返回一个传递给 localFinally 委托的状态值。Finally, the last body invocation on each task returns a state value that is passed to the localFinally delegate. 每个任务调用一次 localFinally 委托,以便对每个任务的本地状态执行最后一个操作。The localFinally delegate is invoked once per task to perform a final action on each task's local state. 可对多个任务同时调用此委托;因此,必须同步对任何共享变量的访问。This delegate might be invoked concurrently on multiple tasks; therefore, you must synchronize access to any shared variables.

当现有任务完成并被新任务替换时,Parallel.For 方法可能使用比线程多的任务,而不是使用线程。The Parallel.For method may use more tasks than threads over the lifetime of its execution, as existing tasks complete and are replaced by new tasks. 这为底层 TaskScheduler 对象提供了添加、更改或删除服务循环的线程的机会。This gives the underlying TaskScheduler object the chance to add, change, or remove threads that service the loop.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, then the method returns immediately without performing any iterations.

有关使用此方法的示例,请参阅 how to: Write a Parallel For Loop With Thread 局部变量For an example that uses this method, see How to: Write a Parallel.For Loop with Thread-Local Variables.

另请参阅

For<TLocal>(Int64, Int64, Func<TLocal>, Func<Int64,ParallelLoopState,TLocal,TLocal>, Action<TLocal>)

执行具有 64 位索引和线程本地数据的 for 循环,其中可能会并行运行迭代,而且可以监视和操作循环的状态。Executes a for loop with 64-bit indexes and thread-local data in which iterations may run in parallel, and the state of the loop can be monitored and manipulated.

public:
generic <typename TLocal>
 static System::Threading::Tasks::ParallelLoopResult For(long fromInclusive, long toExclusive, Func<TLocal> ^ localInit, Func<long, System::Threading::Tasks::ParallelLoopState ^, TLocal, TLocal> ^ body, Action<TLocal> ^ localFinally);
public static System.Threading.Tasks.ParallelLoopResult For<TLocal> (long fromInclusive, long toExclusive, Func<TLocal> localInit, Func<long,System.Threading.Tasks.ParallelLoopState,TLocal,TLocal> body, Action<TLocal> localFinally);
static member For : int64 * int64 * Func<'Local> * Func<int64, System.Threading.Tasks.ParallelLoopState, 'Local, 'Local> * Action<'Local> -> System.Threading.Tasks.ParallelLoopResult
Public Shared Function For(Of TLocal) (fromInclusive As Long, toExclusive As Long, localInit As Func(Of TLocal), body As Func(Of Long, ParallelLoopState, TLocal, TLocal), localFinally As Action(Of TLocal)) As ParallelLoopResult

类型参数

TLocal

线程本地数据的类型。The type of the thread-local data.

参数

fromInclusive
Int64

开始索引(含)。The start index, inclusive.

toExclusive
Int64

结束索引(不含)。The end index, exclusive.

localInit
Func<TLocal>

用于返回每个任务的本地数据的初始状态的函数委托。The function delegate that returns the initial state of the local data for each task.

body
Func<Int64,ParallelLoopState,TLocal,TLocal>

将为每个迭代调用一次的委托。The delegate that is invoked once per iteration.

localFinally
Action<TLocal>

用于对每个任务的本地状态执行一个最终操作的委托。The delegate that performs a final action on the local state of each task.

返回

ParallelLoopResult

包含有关已完成的循环部分的信息的结构。A structure that contains information about which portion of the loop completed.

例外

body 参数为 nullThe body argument is null.

- 或 --or- localInit 参数为 nullThe localInit argument is null.

- 或 --or- localFinally 参数为 nullThe localFinally argument is null.

包含在所有线程上引发的全部单个异常的异常。The exception that contains all the individual exceptions thrown on all threads.

注解

对于迭代范围(fromInclusivetoExclusive)中的每个值调用一次 body 委托。The body delegate is invoked once for each value in the iteration range (fromInclusive, toExclusive). 它提供有以下参数:迭代数(Int64)、可能用于提前跳出循环的 ParallelLoopState 实例,以及可能在同一任务上执行的迭代之间共享的某些本地状态。It is provided with the following parameters: the iteration count (Int64), a ParallelLoopState instance that may be used to break out of the loop prematurely, and some local state that may be shared amongst iterations that execute on the same task.

对于参与循环执行的每个任务调用一次 localInit 委托,并返回每个任务的初始本地状态。The localInit delegate is invoked once for each task that participates in the loop's execution and returns the initial local state for each of those tasks. 这些初始状态将传递给每个任务上的第一个 body 调用。These initial states are passed to the first body invocations on each task. 然后,每个后续的主体调用都将返回一个可能修改的状态值,并将其传递给下一个主体调用。Then, every subsequent body invocation returns a possibly modified state value that is passed to the next body invocation. 最后,每个任务的最后一个主体调用返回一个传递给 localFinally 委托的状态值。Finally, the last body invocation on each task returns a state value that is passed to the localFinally delegate. 每个任务调用一次 localFinally 委托,以便对每个任务的本地状态执行最后一个操作。The localFinally delegate is invoked once per task to perform a final action on each task's local state. 可对多个任务同时调用此委托;因此,必须同步对任何共享变量的访问。This delegate might be invoked concurrently on multiple tasks; therefore, you must synchronize access to any shared variables.

当现有任务完成并被新任务替换时,Parallel.For 方法可能使用比线程多的任务,而不是使用线程。The Parallel.For method may use more tasks than threads over the lifetime of its execution, as existing tasks complete and are replaced by new tasks. 这为底层 TaskScheduler 对象提供了添加、更改或删除服务循环的线程的机会。This gives the underlying TaskScheduler object the chance to add, change, or remove threads that service the loop.

如果 fromInclusive 大于或等于 toExclusive,则方法立即返回,而不执行任何迭代。If fromInclusive is greater than or equal to toExclusive, then the method returns immediately without performing any iterations.

有关使用此方法的示例,请参阅 how to: Write a Parallel For Loop With Thread 局部变量For an example that uses this method, see How to: Write a Parallel.For Loop with Thread-Local Variables.

另请参阅

适用于