Table of Contents

Extensions for System.Threading.SynchronizationContext

PostDelayed() and CancelDelayed()

To post a call-back to given SynchronizationContext and execute it after given delay time. Actually it holds the call-back when you call PostDelayed(), and calls Post() to given SynchronizationContext automatically after the given delay time.

After calling PostDelayed() you will get a token reprensents the delayed call-back you post. You can call CancelDelayed() if you want to cancel it before call-back execution.

// Post a call-back and execute it after 500ms.
var token = SynchronizationContext.Current?.Post(() =>
{
    ...
}, 500);

// Cancel call-back.
SynchronizationContext.Current?.CancelDelayed(token);

SingleThreadSynchronizationContext

Implementation of System.Threading.SynchronizationContext which creates a dedicated Thread to execute all call-backs posted to it. Because it holds a Thread inside, you need to call Dispose() when it is no longer needed.

FixedThreadsTaskScheduler

Implementation of System.Threading.Tasks.TaskScheduler which creates one or more dedicated and fixed Threads to execute tasks according to its maximum concurrency level. Because it holds Threads inside, you need to call Dispose() when it is no longer needed.

// Create task scheduler with maximum concurrency level be 4.
readonly FixedThreadsTaskScheduler taskScheduler = new FixedThreadsTaskScheduler(4);
readonly TaskFactory taskFactory = new TaskFactory(taskScheduler);

// Run a task by the scheduler.
await taskFactory.StartNew(() =>
{
    // Run task here.
});

// Dispose the scheduler to make sure no threads left.
taskScheduler.Dispose();

ScheduledAction

Represents an action which can be executed by specific SynchronizationContext, you can call Schedule() to schedule it with or without delay time. Once you call Schedule(), no more Schedule() allowed (call without effect) before its execution unless you call:

  • Cancel() to cancel scheduled execution.
  • Execute() to cancel scheduled execution and execute immediately.
  • ExecuteIfScheduled() to execute immediately if it has been scheduled (scheduled execution will be cancelled).
  • Reschedule() to override scheduled execution.

The class is designed to help you to eliminate unnecessary action execution to improve performance.

// Create ScheduledAction which binds to the SynchronizationContext on current thread.
readonly ScheduledAction saveWindowSizeToSettingsAction = new ScheduledAction(() =>
{
    // Code to save size of window to settings.
});

protected override void OnWindowSizeChanged()
{
    // Schedule to save size 500ms later.
    // The call to Schedule() may be no effect if it has been scheduled but not executed yet.
    // The action will be executed 500ms later from the first call to Schedule().
    saveWindowSizeToSettingsAction.Schedule(500);
    ...
}

protected override void OnWindowClosing()
{
    // Save size immediately no matter it has been scheduled or not.
    saveWindowSizeToSettingsAction.Execute();
    ...
}
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