我有一个简单的(没有升级或超时)ReaderWriterLock的采用实现,是为Silverlight设计的。我想知道是否有专业人士可以验证它的设计好坏。对我来说,它看起来还不错,它按照广告所说的工作,但我对多线程代码的经验有限。
public sealed class ReaderWriterLock
{
private readonly object syncRoot = new object(); // Internal lock.
private int i = 0; // 0 or greater means readers can pass; -1 is active writer.
private int readWaiters = 0; // Readers waiting for writer to exit.
private int writeWaiters = 0; // Writers waiting for writer lock.
private ConditionVariable conditionVar; // Condition variable.
public ReaderWriterLock()
{
conditionVar = new ConditionVariable(syncRoot);
}
/// <summary>
/// Gets a value indicating if a reader lock is held.
/// </summary>
public bool IsReaderLockHeld
{
get
{
lock ( syncRoot )
{
if ( i > 0 )
return true;
return false;
}
}
}
/// <summary>
/// Gets a value indicating if the writer lock is held.
/// </summary>
public bool IsWriterLockHeld
{
get
{
lock ( syncRoot )
{
if ( i < 0 )
return true;
return false;
}
}
}
/// <summary>
/// Aquires the writer lock.
/// </summary>
public void AcquireWriterLock()
{
lock ( syncRoot )
{
writeWaiters++;
while ( i != 0 )
conditionVar.Wait(); // Wait until existing writer frees the lock.
writeWaiters--;
i = -1; // Thread has writer lock.
}
}
/// <summary>
/// Aquires a reader lock.
/// </summary>
public void AcquireReaderLock()
{
lock ( syncRoot )
{
readWaiters++;
// Defer to a writer (one time only) if one is waiting to prevent writer starvation.
if ( writeWaiters > 0 )
{
conditionVar.Pulse();
Monitor.Wait(syncRoot);
}
while ( i < 0 )
Monitor.Wait(syncRoot);
readWaiters--;
i++;
}
}
/// <summary>
/// Releases the writer lock.
/// </summary>
public void ReleaseWriterLock()
{
bool doPulse = false;
lock ( syncRoot )
{
i = 0;
// Decide if we pulse a writer or readers.
if ( readWaiters > 0 )
{
Monitor.PulseAll(syncRoot); // If multiple readers waiting, pulse them all.
}
else
{
doPulse = true;
}
}
if ( doPulse )
conditionVar.Pulse(); // Pulse one writer if one waiting.
}
/// <summary>
/// Releases a reader lock.
/// </summary>
public void ReleaseReaderLock()
{
bool doPulse = false;
lock ( syncRoot )
{
i--;
if ( i == 0 )
doPulse = true;
}
if ( doPulse )
conditionVar.Pulse(); // Pulse one writer if one waiting.
}
/// <summary>
/// Condition Variable (CV) class.
/// </summary>
public class ConditionVariable
{
private readonly object syncLock = new object(); // Internal lock.
private readonly object m; // The lock associated with this CV.
public ConditionVariable(object m)
{
lock (syncLock)
{
this.m = m;
}
}
public void Wait()
{
bool enter = false;
try
{
lock (syncLock)
{
Monitor.Exit(m);
enter = true;
Monitor.Wait(syncLock);
}
}
finally
{
if (enter)
Monitor.Enter(m);
}
}
public void Pulse()
{
lock (syncLock)
{
Monitor.Pulse(syncLock);
}
}
public void PulseAll()
{
lock (syncLock)
{
Monitor.PulseAll(syncLock);
}
}
}
}
如果它很好,那么它可能对其他人也有帮助,因为Silverlight目前缺少读写锁。谢谢。