SpinLock 结构

定义

提供一个相互排斥锁基元,在该基元中,尝试获取锁的线程将在重复检查的循环中等待,直至该锁变为可用为止。Provides a mutual exclusion lock primitive where a thread trying to acquire the lock waits in a loop repeatedly checking until the lock becomes available.

public value class SpinLock
public struct SpinLock
[System.Runtime.InteropServices.ComVisible(false)]
public struct SpinLock
type SpinLock = struct
Public Structure SpinLock
继承
SpinLock
属性

示例

下面的示例演示如何使用 SpinLockThe following example shows how to use a SpinLock:

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

class SpinLockDemo
{

    // Demonstrates:
    //      Default SpinLock construction ()
    //      SpinLock.Enter(ref bool)
    //      SpinLock.Exit()
    static void SpinLockSample1()
    {
        SpinLock sl = new SpinLock();

        StringBuilder sb = new StringBuilder();

        // Action taken by each parallel job.
        // Append to the StringBuilder 10000 times, protecting
        // access to sb with a SpinLock.
        Action action = () =>
        {
            bool gotLock = false;
            for (int i = 0; i < 10000; i++)
            {
                gotLock = false;
                try
                {
                    sl.Enter(ref gotLock);
                    sb.Append((i % 10).ToString());
                }
                finally
                {
                    // Only give up the lock if you actually acquired it
                    if (gotLock) sl.Exit();
                }
            }
        };

        // Invoke 3 concurrent instances of the action above
        Parallel.Invoke(action, action, action);

        // Check/Show the results
        Console.WriteLine("sb.Length = {0} (should be 30000)", sb.Length);
        Console.WriteLine("number of occurrences of '5' in sb: {0} (should be 3000)",
            sb.ToString().Where(c => (c == '5')).Count());
    }

    // Demonstrates:
    //      Default SpinLock constructor (tracking thread owner)
    //      SpinLock.Enter(ref bool)
    //      SpinLock.Exit() throwing exception
    //      SpinLock.IsHeld
    //      SpinLock.IsHeldByCurrentThread
    //      SpinLock.IsThreadOwnerTrackingEnabled
    static void SpinLockSample2()
    {
        // Instantiate a SpinLock
        SpinLock sl = new SpinLock();

        // These MRESs help to sequence the two jobs below
        ManualResetEventSlim mre1 = new ManualResetEventSlim(false);
        ManualResetEventSlim mre2 = new ManualResetEventSlim(false);
        bool lockTaken = false;

        Task taskA = Task.Factory.StartNew(() =>
        {
            try
            {
                sl.Enter(ref lockTaken);
                Console.WriteLine("Task A: entered SpinLock");
                mre1.Set(); // Signal Task B to commence with its logic

                // Wait for Task B to complete its logic
                // (Normally, you would not want to perform such a potentially
                // heavyweight operation while holding a SpinLock, but we do it
                // here to more effectively show off SpinLock properties in
                // taskB.)
                mre2.Wait();
            }
            finally
            {
                if (lockTaken) sl.Exit();
            }
        });

        Task taskB = Task.Factory.StartNew(() =>
        {
            mre1.Wait(); // wait for Task A to signal me
            Console.WriteLine("Task B: sl.IsHeld = {0} (should be true)", sl.IsHeld);
            Console.WriteLine("Task B: sl.IsHeldByCurrentThread = {0} (should be false)", sl.IsHeldByCurrentThread);
            Console.WriteLine("Task B: sl.IsThreadOwnerTrackingEnabled = {0} (should be true)", sl.IsThreadOwnerTrackingEnabled);

            try
            {
                sl.Exit();
                Console.WriteLine("Task B: Released sl, should not have been able to!");
            }
            catch (Exception e)
            {
                Console.WriteLine("Task B: sl.Exit resulted in exception, as expected: {0}", e.Message);
            }

            mre2.Set(); // Signal Task A to exit the SpinLock
        });

        // Wait for task completion and clean up
        Task.WaitAll(taskA, taskB);
        mre1.Dispose();
        mre2.Dispose();
    }

    // Demonstrates:
    //      SpinLock constructor(false) -- thread ownership not tracked
    static void SpinLockSample3()
    {
        // Create SpinLock that does not track ownership/threadIDs
        SpinLock sl = new SpinLock(false);

        // Used to synchronize with the Task below
        ManualResetEventSlim mres = new ManualResetEventSlim(false);

        // We will verify that the Task below runs on a separate thread
        Console.WriteLine("main thread id = {0}", Thread.CurrentThread.ManagedThreadId);

        // Now enter the SpinLock.  Ordinarily, you would not want to spend so
        // much time holding a SpinLock, but we do it here for the purpose of 
        // demonstrating that a non-ownership-tracking SpinLock can be exited 
        // by a different thread than that which was used to enter it.
        bool lockTaken = false;
        sl.Enter(ref lockTaken);

        // Create a separate Task from which to Exit() the SpinLock
        Task worker = Task.Factory.StartNew(() =>
        {
            Console.WriteLine("worker task thread id = {0} (should be different than main thread id)",
                Thread.CurrentThread.ManagedThreadId);

            // Now exit the SpinLock
            try
            {
                sl.Exit();
                Console.WriteLine("worker task: successfully exited SpinLock, as expected");
            }
            catch (Exception e)
            {
                Console.WriteLine("worker task: unexpected failure in exiting SpinLock: {0}", e.Message);
            }

            // Notify main thread to continue
            mres.Set();
        });

        // Do this instead of worker.Wait(), because worker.Wait() could inline the worker Task,
        // causing it to be run on the same thread.  The purpose of this example is to show that
        // a different thread can exit the SpinLock created (without thread tracking) on your thread.
        mres.Wait();

        // now Wait() on worker and clean up
        worker.Wait();
        mres.Dispose();
    }
}
Imports System.Text
Imports System.Threading
Imports System.Threading.Tasks


Module SpinLockDemo

    ' Demonstrates:
    ' Default SpinLock construction ()
    ' SpinLock.Enter(ref bool)
    ' SpinLock.Exit()
    Private Sub SpinLockSample1()
        Dim sl As New SpinLock()

        Dim sb As New StringBuilder()

        ' Action taken by each parallel job.
        ' Append to the StringBuilder 10000 times, protecting
        ' access to sb with a SpinLock.
        Dim action As Action =
            Sub()
                Dim gotLock As Boolean = False
                For i As Integer = 0 To 9999
                    gotLock = False
                    Try
                        sl.Enter(gotLock)
                        sb.Append((i Mod 10).ToString())
                    Finally
                        ' Only give up the lock if you actually acquired it
                        If gotLock Then
                            sl.[Exit]()
                        End If
                    End Try
                Next
            End Sub

        ' Invoke 3 concurrent instances of the action above
        Parallel.Invoke(action, action, action)

        ' Check/Show the results
        Console.WriteLine("sb.Length = {0} (should be 30000)", sb.Length)
        Console.WriteLine("number of occurrences of '5' in sb: {0} (should be 3000)", sb.ToString().Where(Function(c) (c = "5"c)).Count())
    End Sub

    ' Demonstrates:
    ' Default SpinLock constructor (tracking thread owner)
    ' SpinLock.Enter(ref bool)
    ' SpinLock.Exit() throwing exception
    ' SpinLock.IsHeld
    ' SpinLock.IsHeldByCurrentThread
    ' SpinLock.IsThreadOwnerTrackingEnabled
    Private Sub SpinLockSample2()
        ' Instantiate a SpinLock
        Dim sl As New SpinLock()

        ' These MRESs help to sequence the two jobs below
        Dim mre1 As New ManualResetEventSlim(False)
        Dim mre2 As New ManualResetEventSlim(False)
        Dim lockTaken As Boolean = False

        Dim taskA As Task = Task.Factory.StartNew(
            Sub()
                Try
                    sl.Enter(lockTaken)
                    Console.WriteLine("Task A: entered SpinLock")
                    mre1.[Set]()
                    ' Signal Task B to commence with its logic
                    ' Wait for Task B to complete its logic
                    ' (Normally, you would not want to perform such a potentially
                    ' heavyweight operation while holding a SpinLock, but we do it
                    ' here to more effectively show off SpinLock properties in
                    ' taskB.)
                    mre2.Wait()
                Finally
                    If lockTaken Then
                        sl.[Exit]()
                    End If
                End Try
            End Sub)

        Dim taskB As Task = Task.Factory.StartNew(
            Sub()
                mre1.Wait()
                ' wait for Task A to signal me
                Console.WriteLine("Task B: sl.IsHeld = {0} (should be true)", sl.IsHeld)
                Console.WriteLine("Task B: sl.IsHeldByCurrentThread = {0} (should be false)", sl.IsHeldByCurrentThread)
                Console.WriteLine("Task B: sl.IsThreadOwnerTrackingEnabled = {0} (should be true)", sl.IsThreadOwnerTrackingEnabled)

                Try
                    sl.[Exit]()
                    Console.WriteLine("Task B: Released sl, should not have been able to!")
                Catch e As Exception
                    Console.WriteLine("Task B: sl.Exit resulted in exception, as expected: {0}", e.Message)
                End Try

                ' Signal Task A to exit the SpinLock
                mre2.[Set]()
            End Sub)

        ' Wait for task completion and clean up
        Task.WaitAll(taskA, taskB)
        mre1.Dispose()
        mre2.Dispose()
    End Sub

    ' Demonstrates:
    ' SpinLock constructor(false) -- thread ownership not tracked
    Private Sub SpinLockSample3()
        ' Create SpinLock that does not track ownership/threadIDs
        Dim sl As New SpinLock(False)

        ' Used to synchronize with the Task below
        Dim mres As New ManualResetEventSlim(False)

        ' We will verify that the Task below runs on a separate thread
        Console.WriteLine("main thread id = {0}", Thread.CurrentThread.ManagedThreadId)

        ' Now enter the SpinLock.  Ordinarily, you would not want to spend so
        ' much time holding a SpinLock, but we do it here for the purpose of 
        ' demonstrating that a non-ownership-tracking SpinLock can be exited 
        ' by a different thread than that which was used to enter it.
        Dim lockTaken As Boolean = False
        sl.Enter(lockTaken)

        ' Create a separate Task
        Dim worker As Task = Task.Factory.StartNew(
            Sub()
                Console.WriteLine("worker task thread id = {0} (should be different than main thread id)", Thread.CurrentThread.ManagedThreadId)

                ' Now exit the SpinLock
                Try
                    sl.[Exit]()
                    Console.WriteLine("worker task: successfully exited SpinLock, as expected")
                Catch e As Exception
                    Console.WriteLine("worker task: unexpected failure in exiting SpinLock: {0}", e.Message)
                End Try

                ' Notify main thread to continue
                mres.[Set]()
            End Sub)

        ' Do this instead of worker.Wait(), because worker.Wait() could inline the worker Task,
        ' causing it to be run on the same thread. The purpose of this example is to show that
        ' a different thread can exit the SpinLock created (without thread tracking) on your thread.
        mres.Wait()

        ' now Wait() on worker and clean up
        worker.Wait()
        mres.Dispose()
    End Sub


End Module

注解

有关如何使用旋转锁定的示例,请参阅如何:使用旋转锁进行低级别同步For an example of how to use a Spin Lock, see How to: Use SpinLock for Low-Level Synchronization.

自旋锁可用于叶级锁,在这种情况下,使用 Monitor、大小或垃圾回收压力所隐含的对象分配非常昂贵。Spin locks can be used for leaf-level locks where the object allocation implied by using a Monitor, in size or due to garbage collection pressure, is overly expensive. 旋转锁定有助于避免阻塞;但是,如果你预计会有大量的阻塞,则可能由于旋转过多而无法使用自旋锁。A spin lock can be useful to avoid blocking; however, if you expect a significant amount of blocking, you should probably not use spin locks due to excessive spinning. 当锁的粒度较大且数值较大(例如,链接列表中的每个节点都有一个锁)以及锁保留时间始终极短时,旋转可能非常有利。Spinning can be beneficial when locks are fine-grained and large in number (for example, a lock per node in a linked list) and also when lock hold-times are always extremely short. 通常,在持有自旋锁时,应避免使用以下任何操作:In general, while holding a spin lock, one should avoid any of these actions:

  • 堵塞blocking,

  • 调用自身可能会阻止的任何内容,calling anything that itself may block,

  • 同时保留多个自旋锁,holding more than one spin lock at once,

  • 进行动态调度的调用(interface 和虚方法),making dynamically dispatched calls (interface and virtuals),

  • 对任何代码进行静态调度调用,而不是任何代码,或making statically dispatched calls into any code one doesn't own, or

  • 分配内存。allocating memory.

只有在确定这样做后,才应使用 SpinLock 会提高应用程序的性能。SpinLock should only be used after you have been determined that doing so will improve an application's performance. 请注意,出于性能方面的原因,SpinLock 是值类型。It is also important to note that SpinLock is a value type, for performance reasons. 出于此原因,必须注意不要意外复制 SpinLock 实例,因为两个实例(原始和副本)将完全独立,这可能会导致应用程序出现错误的行为。For this reason, you must be very careful not to accidentally copy a SpinLock instance, as the two instances (the original and the copy) would then be completely independent of one another, which would likely lead to erroneous behavior of the application. 如果 SpinLock 实例必须是传递的,则应通过引用而不是按值传递。If a SpinLock instance must be passed around, it should be passed by reference rather than by value.

不要将 SpinLock 实例存储在只读字段中。Do not store SpinLock instances in readonly fields.

构造函数

SpinLock(Boolean)

使用用于跟踪线程 ID 以改善调试的选项初始化 SpinLock 结构的新实例。Initializes a new instance of the SpinLock structure with the option to track thread IDs to improve debugging.

属性

IsHeld

获取锁当前是否已由任何线程占用。Gets whether the lock is currently held by any thread.

IsHeldByCurrentThread

获取锁是否已由当前线程占用。Gets whether the lock is held by the current thread.

IsThreadOwnerTrackingEnabled

获取是否已为此实例启用了线程所有权跟踪。Gets whether thread ownership tracking is enabled for this instance.

方法

Enter(Boolean)

采用可靠的方式获取锁,这样,即使在方法调用中发生异常的情况下,都能采用可靠的方式检查 lockTaken 以确定是否已获取锁。Acquires the lock in a reliable manner, such that even if an exception occurs within the method call, lockTaken can be examined reliably to determine whether the lock was acquired.

Exit()

释放锁。Releases the lock.

Exit(Boolean)

释放锁。Releases the lock.

TryEnter(Boolean)

尝试采用可靠的方式获取锁,这样,即使在方法调用中发生异常的情况下,都能采用可靠的方式检查 lockTaken 以确定是否已获取锁。Attempts to acquire the lock in a reliable manner, such that even if an exception occurs within the method call, lockTaken can be examined reliably to determine whether the lock was acquired.

TryEnter(Int32, Boolean)

尝试采用可靠的方式获取锁,这样,即使在方法调用中发生异常的情况下,都能采用可靠的方式检查 lockTaken 以确定是否已获取锁。Attempts to acquire the lock in a reliable manner, such that even if an exception occurs within the method call, lockTaken can be examined reliably to determine whether the lock was acquired.

TryEnter(TimeSpan, Boolean)

尝试采用可靠的方式获取锁,这样,即使在方法调用中发生异常的情况下,都能采用可靠的方式检查 lockTaken 以确定是否已获取锁。Attempts to acquire the lock in a reliable manner, such that even if an exception occurs within the method call, lockTaken can be examined reliably to determine whether the lock was acquired.

适用于

线程安全性

SpinLock 的所有成员都是线程安全的,可同时从多个线程使用。All members of SpinLock are thread-safe and may be used from multiple threads concurrently.

另请参阅