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Andrew Arnott
Andrew Arnott

Reputation: 81821

How to wait on WaitHandle without message pumping?

I want to call WaitHandle.WaitOne(TimeSpan) in .NET, but I'm on the STA thread and it pumps messages while waiting. For reasons that are beyond the scope of this question, I need to wait without pumping. How can I wait for a WaitHandle to be signaled without pumping messages?

It seems in some scenarios that WaitHandle.WaitOne does not pump messages. But it does sometimes for some messages. See these links for more information on that:

  1. Managed and Unmanaged Threading in Microsoft Windows
  2. Managed blocking

Upvotes: 11

Views: 3383

Answers (3)

Andrew Arnott
Andrew Arnott

Reputation: 81821

If you're in a WPF app where the Dispatcher is the one running the message pumps during managed waits, the simplest way to disable the message pump during your wait is via Dispatcher.DisableProcessing:

// The Dispose() method is called at the end of the using statement. 
// Calling Dispose on the DispatcherProcessingDisabled structure,  
// which is returned from the call to DisableProcessing, will 
// re-enable Dispatcher processing. 
using (Dispatcher.CurrentDispatcher.DisableProcessing())
{
    // Do work while the dispatcher processing is disabled.
    Thread.Sleep(2000);
}

Upvotes: 1

russilwvong
russilwvong

Reputation: 53

Apparently this was a change introduced in Microsoft Vista: CoWaitForMultipleHandles now dispatches WM_PAINT messages.

Vista bug report.

A workaround is to use Microsoft's Application Compatibility Toolkit to set the DisableNewWMPAINTDispatchInOLE flag for your application.

Upvotes: 3

x0n
x0n

Reputation: 52480

WaitForSingleObject or WaitForMultipleObjects are non-pumping waits; use p/invoke.

[DllImport("kernel32", SetLastError=true, ExactSpelling=true)]
public static extern Int32 WaitForSingleObject(SafeWaitHandle handle, Int32 milliseconds);

-Oisin

Upvotes: 9

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