Posted by: Dakusan
« on: January 09, 2013, 11:18:00 pm »Original post for Thread synchronization in C# can be found at https://www.castledragmire.com/Posts/Thread_synchronization_in_C%23.
Originally posted on: 01/09/13
Originally posted on: 01/09/13
I have been working heavily in C# CE (Compact Edition) v2.0 for the last 2 years for clients, and one of the very many things that I was never really happy with (in at least that version of the language, though it looks like it might plague all versions of C#) is the available thread synchronization tools. I’ve come to love the lock/wait/notify model (in Java it’s synchronized/wait/notify and in Perl it’s lock/cond_wait/cond_signal), but I have found nothing as intuitive and safe to use in C#. To alleviate this, I went ahead and wrote my own ThreadLockAndWait class that achieves this functionality.
This works the same as the POSIX lock, unlock, cond_wait, cond_signal, and cond_timedwait functions, except:
- Lock is not required before CondSignal (it does its own inner lock and unlock)
- If ReacquireLockAfterWait is false, in which case CondWait will not lock again after signaled and just continue immediately
- Only 1 thread can be CondWaiting at a time (If one is CondWaiting and is signaled but not reacquired the lock, its ok for another to start CondWaiting)
public class ThreadLockAndWait
{
private Mutex TheLock=new Mutex(), CondWaitLock=new Mutex(); //CondWaitLock makes sure 1 thread stops waiting before the next one starts waiting
private ManualResetEvent WaitTimer=new ManualResetEvent(false);
private string OwnersThreadName=null;
private int OwnerLockCount=0;
public void Lock()
{
TheLock.WaitOne();
if(OwnerLockCount++==0)
OwnersThreadName=Thread.CurrentThread.Name;
}
public void UnLock()
{
TheLock.WaitOne();
if(OwnerLockCount==0)
{
TheLock.ReleaseMutex();
throw new Exception("Cannot unlock if not locked");
}
TheLock.ReleaseMutex();
if(--OwnerLockCount==0)
OwnersThreadName=null;
TheLock.ReleaseMutex();
}
public void CondWait() { RealCondWait(-1, true); }
public void CondWait(bool ReacquireLockAfterWait) { RealCondWait(-1, ReacquireLockAfterWait); }
public void CondTimedWait(int TimeToWait) { RealCondWait(Math.Max(0, TimeToWait), true); }
public void CondTimedWait(int TimeToWait, bool ReacquireLockAfterWait) { RealCondWait(Math.Max(0, TimeToWait), ReacquireLockAfterWait); }
private void RealCondWait(int TimeToWait, bool ReacquireLockAfterWait)
{
//Prepare to wait
TheLock.WaitOne();
if(OwnerLockCount==0)
{
TheLock.ReleaseMutex();
throw new Exception("Cannot wait if not locked");
}
CondWaitLock.WaitOne(); //Release this wait before the next one starts
WaitTimer.Reset();
TheLock.ReleaseMutex();
//Release all locks
int PreviousLockCount=OwnerLockCount;
OwnersThreadName=null;
OwnerLockCount=0;
if(PreviousLockCount!=1)
System.Diagnostics.Debug.Print("Warning, mutex has multiple locks from thread!");
for(int i=0;i<PreviousLockCount;i++)
TheLock.ReleaseMutex();
//Wait
if(TimeToWait>0)
WaitTimer.WaitOne(TimeToWait, false);
else if(TimeToWait!=0)
WaitTimer.WaitOne();
CondWaitLock.ReleaseMutex();
//Reacquire lock
if(!ReacquireLockAfterWait)
return;
for(int i=0;i<PreviousLockCount;i++)
TheLock.WaitOne();
OwnerLockCount=PreviousLockCount;
OwnersThreadName=Thread.CurrentThread.Name;
}
public void CondSignal()
{
TheLock.WaitOne();
WaitTimer.Set();
TheLock.ReleaseMutex();
}
}