ReaderWriterLock.UpgradeToWriterLock 方法

定义

将读线程锁升级为写线程锁。Upgrades a reader lock to the writer lock.

重载

UpgradeToWriterLock(Int32)

使用一个 Int32 超时值将读线程锁升级为写线程锁。Upgrades a reader lock to the writer lock, using an Int32 value for the time-out.

UpgradeToWriterLock(TimeSpan)

使用一个 TimeSpan 超时值将读线程锁升级为写线程锁。Upgrades a reader lock to the writer lock, using a TimeSpan value for the time-out.

UpgradeToWriterLock(Int32)

使用一个 Int32 超时值将读线程锁升级为写线程锁。Upgrades a reader lock to the writer lock, using an Int32 value for the time-out.

public:
 System::Threading::LockCookie UpgradeToWriterLock(int millisecondsTimeout);
public System.Threading.LockCookie UpgradeToWriterLock (int millisecondsTimeout);
member this.UpgradeToWriterLock : int -> System.Threading.LockCookie
Public Function UpgradeToWriterLock (millisecondsTimeout As Integer) As LockCookie

参数

millisecondsTimeout
Int32

以毫秒为单位的超时。The time-out in milliseconds.

返回

LockCookie

一个 LockCookie 值。A LockCookie value.

例外

millisecondsTimeout 在授予锁定请求前过期。millisecondsTimeout expires before the lock request is granted.

示例

下面的代码示例演示如何请求读取器锁,将读取器锁升级到写入器锁,并再次降级到读取器锁。The following code example shows how to request a reader lock, upgrade the reader lock to a writer lock, and downgrade to a reader lock again.

此代码是为 ReaderWriterLock 类提供的更大示例的一部分。This code is part of a larger example provided for the ReaderWriterLock class.

// The complete code is located in the ReaderWriterLock
// class topic.
using namespace System;
using namespace System::Threading;
public ref class Test
{
public:

   // Declaring the ReaderWriterLock at the class level
   // makes it visible to all threads.
   static ReaderWriterLock^ rwl = gcnew ReaderWriterLock;

   // For this example, the shared resource protected by the
   // ReaderWriterLock is just an integer.
   static int resource = 0;

// The complete code is located in the ReaderWriterLock class topic.
using System;
using System.Threading;

public class Example
{
   static ReaderWriterLock rwl = new ReaderWriterLock();
   // Define the shared resource protected by the ReaderWriterLock.
   static int resource = 0;
' The complete code is located in the ReaderWriterLock class topic.
Imports System.Threading

Public Module Example
   Private rwl As New ReaderWriterLock()
   ' Define the shared resource protected by the ReaderWriterLock.
   Private resource As Integer = 0
// Shows how to request a reader lock, upgrade the
// reader lock to the writer lock, and downgrade to a
// reader lock again.
static void UpgradeDowngrade( Random^ rnd, int timeOut )
{
   try
   {
      rwl->AcquireReaderLock( timeOut );
      try
      {

         // It is safe for this thread to read from
         // the shared resource.
         Display( String::Format( "reads resource value {0}", resource ) );
         Interlocked::Increment( reads );

         // If it is necessary to write to the resource,
         // you must either release the reader lock and
         // then request the writer lock, or upgrade the
         // reader lock. Note that upgrading the reader lock
         // puts the thread in the write queue, behind any
         // other threads that might be waiting for the
         // writer lock.
         try
         {
            LockCookie lc = rwl->UpgradeToWriterLock( timeOut );
            try
            {

               // It is safe for this thread to read or write
               // from the shared resource.
               resource = rnd->Next( 500 );
               Display( String::Format( "writes resource value {0}", resource ) );
               Interlocked::Increment( writes );
            }
            finally
            {

               // Ensure that the lock is released.
               rwl->DowngradeFromWriterLock( lc );
            }

         }
         catch ( ApplicationException^ )
         {

            // The upgrade request timed out.
            Interlocked::Increment( writerTimeouts );
         }


         // When the lock has been downgraded, it is
         // still safe to read from the resource.
         Display( String::Format( "reads resource value {0}", resource ) );
         Interlocked::Increment( reads );
      }
      finally
      {

         // Ensure that the lock is released.
         rwl->ReleaseReaderLock();
      }

   }
   catch ( ApplicationException^ )
   {

      // The reader lock request timed out.
      Interlocked::Increment( readerTimeouts );
   }

}


// Requests a reader lock, upgrades the reader lock to the writer
// lock, and downgrades it to a reader lock again.
static void UpgradeDowngrade(Random rnd, int timeOut)
{
   try {
      rwl.AcquireReaderLock(timeOut);
      try {
         // It's safe for this thread to read from the shared resource.
         Display("reads resource value " + resource);
         Interlocked.Increment(ref reads);

         // To write to the resource, either release the reader lock and
         // request the writer lock, or upgrade the reader lock. Upgrading
         // the reader lock puts the thread in the write queue, behind any
         // other threads that might be waiting for the writer lock.
         try {
            LockCookie lc = rwl.UpgradeToWriterLock(timeOut);
            try {
               // It's safe for this thread to read or write from the shared resource.
               resource = rnd.Next(500);
               Display("writes resource value " + resource);
               Interlocked.Increment(ref writes);
            }
            finally {
               // Ensure that the lock is released.
               rwl.DowngradeFromWriterLock(ref lc);
            }
         }
         catch (ApplicationException) {
            // The upgrade request timed out.
            Interlocked.Increment(ref writerTimeouts);
         }

         // If the lock was downgraded, it's still safe to read from the resource.
         Display("reads resource value " + resource);
         Interlocked.Increment(ref reads);
      }
      finally {
         // Ensure that the lock is released.
         rwl.ReleaseReaderLock();
      }
   }
   catch (ApplicationException) {
      // The reader lock request timed out.
      Interlocked.Increment(ref readerTimeouts);
   }
}
' Requests a reader lock, upgrades the reader lock to the writer
' lock, and downgrades it to a reader lock again.
Sub UpgradeDowngrade(rnd As Random, timeOut As Integer)
   Try
      rwl.AcquireReaderLock(timeOut)
      Try
         ' It's safe for this thread to read from the shared resource.
         Display("reads resource value " & resource)
         Interlocked.Increment(reads)
         
         ' To write to the resource, either release the reader lock and
         ' request the writer lock, or upgrade the reader lock. Upgrading
         ' the reader lock puts the thread in the write queue, behind any
         ' other threads that might be waiting for the writer lock.
         Try
            Dim lc As LockCookie = rwl.UpgradeToWriterLock(timeOut)
            Try
               ' It's safe for this thread to read or write from the shared resource.
               resource = rnd.Next(500)
               Display("writes resource value " & resource)
               Interlocked.Increment(writes)
            Finally
               ' Ensure that the lock is released.
               rwl.DowngradeFromWriterLock(lc)
            End Try
         Catch ex As ApplicationException
            ' The upgrade request timed out.
            Interlocked.Increment(writerTimeouts)
         End Try
         
         ' If the lock was downgraded, it's still safe to read from the resource.
         Display("reads resource value " & resource)
         Interlocked.Increment(reads)
      Finally
         ' Ensure that the lock is released.
         rwl.ReleaseReaderLock()
      End Try
   Catch ex As ApplicationException
      ' The reader lock request timed out.
      Interlocked.Increment(readerTimeouts)
   End Try
End Sub
};


}
End Module

注解

当线程调用时 UpgradeToWriterLock 释放读取器锁,而不考虑锁计数,并且线程将进入写入器锁的队列的末尾。When a thread calls UpgradeToWriterLock the reader lock is released, regardless of the lock count, and the thread goes to the end of the queue for the writer lock. 因此,在向请求升级的线程授予了写入方锁之前,其他线程可能会写入资源。Thus, other threads might write to the resource before the thread that requested the upgrade is granted the writer lock.

重要

在调用 UpgradeToWriterLock 方法的线程可以重新获取读取器锁之前,不会引发超时异常。The time-out exception is not thrown until the thread that called the UpgradeToWriterLock method can reacquire the reader lock. 如果没有其他线程正在等待编写器锁,则会立即发生这种情况。If there are no other threads waiting for the writer lock, this happens immediately. 但是,如果另一个线程排队等候写入器锁,则调用 UpgradeToWriterLock 方法的线程将无法重新获取读取器锁,直到所有当前读取器都释放了锁,并且一个线程已获取并释放了写入器锁。However, if another thread is queued for the writer lock, the thread that called the UpgradeToWriterLock method cannot reacquire the reader lock until all current readers have released their locks, and one thread has acquired and released the writer lock. 即使在当前线程调用了 UpgradeToWriterLock 方法之后,请求编写器锁的其他线程也是如此。This is true even if the other thread that requested the writer lock requested it after the current thread called the UpgradeToWriterLock method.

若要还原锁定状态,请使用 UpgradeToWriterLock返回的 LockCookie 调用 DowngradeFromWriterLockTo restore the lock state, call DowngradeFromWriterLock using the LockCookie returned by UpgradeToWriterLock. 不要将此 LockCookieRestoreLock一起使用。Do not use this LockCookie with RestoreLock.

当线程没有读取器锁时,请不要使用 UpgradeToWriterLockWhen a thread has no reader lock, do not use UpgradeToWriterLock. 请改用 AcquireWriterLockUse AcquireWriterLock instead.

有关有效的超时值,请参阅 ReaderWriterLockFor valid time-out values, see ReaderWriterLock.

另请参阅

UpgradeToWriterLock(TimeSpan)

使用一个 TimeSpan 超时值将读线程锁升级为写线程锁。Upgrades a reader lock to the writer lock, using a TimeSpan value for the time-out.

public:
 System::Threading::LockCookie UpgradeToWriterLock(TimeSpan timeout);
public System.Threading.LockCookie UpgradeToWriterLock (TimeSpan timeout);
member this.UpgradeToWriterLock : TimeSpan -> System.Threading.LockCookie
Public Function UpgradeToWriterLock (timeout As TimeSpan) As LockCookie

参数

timeout
TimeSpan

TimeSpan,用于指定超时时间。The TimeSpan specifying the time-out period.

返回

LockCookie

一个 LockCookie 值。A LockCookie value.

例外

timeout 在授予锁定请求前过期。timeout expires before the lock request is granted.

timeout 可指定 -1 毫秒以外的任何负值。timeout specifies a negative value other than -1 milliseconds.

注解

当线程调用时 UpgradeToWriterLock 释放读取器锁,而不考虑锁计数,并且线程将进入写入器锁的队列的末尾。When a thread calls UpgradeToWriterLock the reader lock is released, regardless of the lock count, and the thread goes to the end of the queue for the writer lock. 因此,在向请求升级的线程授予了写入方锁之前,其他线程可能会写入资源。Thus, other threads might write to the resource before the thread that requested the upgrade is granted the writer lock.

重要

在调用 UpgradeToWriterLock 方法的线程可以重新获取读取器锁之前,不会引发超时异常。The time-out exception is not thrown until the thread that called the UpgradeToWriterLock method can reacquire the reader lock. 如果没有其他线程正在等待编写器锁,则会立即发生这种情况。If there are no other threads waiting for the writer lock, this happens immediately. 但是,如果另一个线程排队等候写入器锁,则调用 UpgradeToWriterLock 方法的线程将无法重新获取读取器锁,直到所有当前读取器都释放了锁,并且一个线程已获取并释放了写入器锁。However, if another thread is queued for the writer lock, the thread that called the UpgradeToWriterLock method cannot reacquire the reader lock until all current readers have released their locks, and one thread has acquired and released the writer lock. 即使在当前线程调用了 UpgradeToWriterLock 方法之后,请求编写器锁的其他线程也是如此。This is true even if the other thread that requested the writer lock requested it after the current thread called the UpgradeToWriterLock method.

若要还原锁定状态,请使用 UpgradeToWriterLock返回的 LockCookie 调用 DowngradeFromWriterLockTo restore the lock state, call DowngradeFromWriterLock using the LockCookie returned by UpgradeToWriterLock. 不要将此 LockCookieRestoreLock一起使用。Do not use this LockCookie with RestoreLock.

当线程没有读取器锁时,请不要使用 UpgradeToWriterLockWhen a thread has no reader lock, do not use UpgradeToWriterLock. 请改用 AcquireWriterLockUse AcquireWriterLock instead.

有关有效的超时值,请参阅 ReaderWriterLockFor valid time-out values, see ReaderWriterLock.

另请参阅

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