Producer-Consumer with a variation - How to synchronize with thread signal/wait?
While working on a large project I realized I was making a lot of calls to be scheduled in the future. Since these were fairly light-weight, I thought it might be better to use a separate scheduler.
ThreadPool.QueueUserWorkItem (() =>
{
Thread.Sleep (5000);
Foo (); // Call is to be executed after sometime
});
So I created a separate scheduler class that runs on its own thread and executes these events. I have 2 functions that access a shared queue from separate threads. I'd use a lock, but since one of the threads needs to sleep-wait, I wasn't sure how to release the lock.
class Scheduler
{
SortedDictionary <DateTime, Action> _queue;
EventWaitHandle _sync;
// Runs on its own thread
void Run ()
{
while (true)
{
// Calculate time till first event
// If queue empty, use pre-defined value
TimeSpan timeDiff = _queue.First().K开发者_C百科ey - DateTime.Now;
// Execute action if in the next 100ms
if (timeDiff < 100ms)
...
// Wait on event handle for time
else
_sync.WaitOne (timeDiff);
}
}
// Can be called by any thread
void ScheduleEvent (Action action, DataTime time)
{
_queue.Add (time, action);
// Signal thread to wake up and check again
_sync.Set ();
}
}
OK, take 2 with Monitor/Pulse.
void Run ()
{
while (true)
{
Action doit = null;
lock(_queueLock)
{
while (_queue.IsEmpty())
Monitor.Wait(_queueLock);
TimeSpan timeDiff = _queue.First().Key - DateTime.Now;
if (timeDiff < 100ms)
doit = _queue.Dequeue();
}
if (doit != null)
; //execute doit
else
_sync.WaitOne (timeDiff);
}
}
void ScheduleEvent (Action action, DataTime time)
{
lock (_queueLock)
{
_queue.Add(time, action);
// Signal thread to wake up and check again
_sync.Set ();
if (_queue.Count == 1)
Monitor.Pulse(_queuLock);
}
}
The problem is easily solved, make sure the WaitOne is outside the lock.
//untested
while (true)
{
Action doit = null;
// Calculate time till first event
// If queue empty, use pre-defined value
lock(_queueLock)
{
TimeSpan timeDiff = _queue.First().Key - DateTime.Now;
if (timeDiff < 100ms)
doit = _queue.Dequeue();
}
if (doit != null)
// execute it
else
_sync.WaitOne (timeDiff);
}
_queueLock is a private helper object.
Since your goal is to schedule a task after a particular period of time, why not just use the System.Threading.Timer? It doesn't require dedicating a thread for the scheduling and takes advantage of the OS to wake up a worker thread. I've used this (removed some comments and other timer service functionality):
public sealed class TimerService : ITimerService
{
public void WhenElapsed(TimeSpan duration, Action callback)
{
if (callback == null) throw new ArgumentNullException("callback");
//Set up state to allow cleanup after timer completes
var timerState = new TimerState(callback);
var timer = new Timer(OnTimerElapsed, timerState, Timeout.Infinite, Timeout.Infinite);
timerState.Timer = timer;
//Start the timer
timer.Change((int) duration.TotalMilliseconds, Timeout.Infinite);
}
private void OnTimerElapsed(Object state)
{
var timerState = (TimerState)state;
timerState.Timer.Dispose();
timerState.Callback();
}
private class TimerState
{
public Timer Timer { get; set; }
public Action Callback { get; private set; }
public TimerState(Action callback)
{
Callback = callback;
}
}
}
The monitores were created for this kind of situation, simple problems that can cost mutch for the application, i present my solution to this very simple and if u want to make a shutdown easy to implement:
void Run()
{
while(true)
lock(this)
{
int timeToSleep = getTimeToSleep() //check your list and return a value
if(timeToSleep <= 100)
action...
else
{
int currTime = Datetime.Now;
int currCount = yourList.Count;
try{
do{
Monitor.Wait(this,timeToSleep);
if(Datetime.now >= (tomeToSleep + currtime))
break; //time passed
else if(yourList.Count != currCount)
break; //new element added go check it
currTime = Datetime.Now;
}while(true);
}
}catch(ThreadInterruptedException e)
{
//do cleanup code or check for shutdown notification
}
}
}
}
void ScheduleEvent (Action action, DataTime time)
{
lock(this)
{
yourlist.add ...
Monitor.Pulse(this);
} }
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