スレッドのロック ステータスを、 UpgradeToWriterLock を呼び出す前の状態に復元します。
Public Sub DowngradeFromWriterLock( _
ByRef lockCookie As LockCookie _)
[C#]
public void DowngradeFromWriterLock( ref LockCookielockCookie);
[C++]
public: void DowngradeFromWriterLock(LockCookie* lockCookie);
[JScript]
public function DowngradeFromWriterLock(
lockCookie : LockCookie);
パラメータ
- lockCookie
UpgradeToWriterLock から返される LockCookie 。
例外
| 例外の種類 | 条件 |
|---|---|
| ApplicationException | スレッドがライタ ロックを保持していません。 |
解説
DowngradeFromWriterLock を呼び出すと、再帰的なロック カウントに関係なく、ライタ ロックが解放され、ライタ ロックにアップグレードする前にスレッドが保持していたリーダー ロックが復元されます。リーダー ロックのロック カウントも復元されます。
メモ DowngradeFromWriterLock は、 UpgradeToWriterLock の呼び出しで取得した LockCookie を受け取ります。 ReleaseLock から返される LockCookie は使用しないでください。
ライタ ロックが解放されたときにリーダー ロックの要求はすべて許可されるため、他のスレッドがライタ ロックを待機している場合でも、ライタ ロックからダウングレードしたときスレッドがブロックすることはありません。
使用例
' The complete code is located in the ReaderWriterLock
' class topic.
Imports System
Imports System.Threading
Imports Microsoft.VisualBasic
Public Class Test
' Declaring the ReaderWriterLock at the class level
' makes it visible to all threads.
Private Shared rwl As New ReaderWriterLock()
' For this example, the shared resource protected by the
' ReaderWriterLock is just an integer.
Private Shared 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.
Shared Sub UpgradeDowngrade(timeOut As Integer)
Try
rwl.AcquireReaderLock(timeOut)
Try
' It is safe for this thread to read from
' the shared resource.
Display("reads resource value " & 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
Dim lc As LockCookie = rwl.UpgradeToWriterLock(timeOut)
Try
' It is 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
' When the lock has been downgraded, it is
' 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 'UpgradeDowngrade
. . .
End Class 'Test
[C#]
// The complete code is located in the ReaderWriterLock
// class topic.
using System;
using System.Threading;
public class Test
{
// Declaring the ReaderWriterLock at the class level
// makes it visible to all threads.
static ReaderWriterLock rwl = new ReaderWriterLock();
// For this example, the shared resource protected by the
// ReaderWriterLock is just an integer.
static int resource = 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(int timeOut)
{
try
{
rwl.AcquireReaderLock(timeOut);
try
{
// It is safe for this thread to read from
// the shared resource.
Display("reads resource value " + resource);
Interlocked.Increment(ref 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("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);
}
// When the lock has been downgraded, it is
// 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);
}
}
. . .
}
[C++]
// The complete code is located in the ReaderWriterLock
// class topic.
#using <mscorlib.dll>
using namespace System;
using namespace System::Threading;
public __gc class Test
{
public:
// Declaring the ReaderWriterLock at the class level
// makes it visible to all threads.
static ReaderWriterLock* rwl = new ReaderWriterLock();
// For this example, the shared resource protected by the
// ReaderWriterLock is just an integer.
static int resource = 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(int timeOut)
{
try
{
rwl->AcquireReaderLock(timeOut);
try
{
// It is safe for this thread to read from
// the shared resource.
Display(String::Format(S"reads resource value {0}", __box(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(S"writes resource value {0}", __box(resource)));
Interlocked::Increment(&writes);
}
__finally
{
// Ensure that the lock is released.
rwl->DowngradeFromWriterLock(__box(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(S"reads resource value {0}", __box(resource)));
Interlocked::Increment(&reads);
}
__finally
{
// Ensure that the lock is released.
rwl->ReleaseReaderLock();
}
}
catch (ApplicationException*)
{
// The reader lock request timed out.
Interlocked::Increment(&readerTimeouts);
}
}
. . .
};
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必要条件
プラットフォーム: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 ファミリ
参照
ReaderWriterLock クラス | ReaderWriterLock メンバ | System.Threading 名前空間 | スレッド処理 | ReaderWriterLock