WaitHandle.WaitAny to match WaitForMultipleObjects functionality

Question

I am porting C++ API code to .NET and looking into function call WaitHandle.WaitAny as a replacement for WaitForMultipleObjects but when debugging with .NET4 i can see that this function is hooked into

private static extern int WaitMultiple(
                               WaitHandle[] waitableSafeHandle, 
                               int msTimeOut, 
                               bool exitContext, 
                               bool WaitAll);

and this makes me think that this function is not sutable for the port. Any other suggestions?

Why not? It allows specify multiple wait handles as well – sll Sep 15 '11 at 13:01 — sll, Sep 15 '11 at 13:01
Why do you think that WaitAny is not suitable? – dtb Sep 15 '11 at 13:02 — dtb, Sep 15 '11 at 13:02

score 8 · Answer 1 · answered Sep 15 '11 at 13:08

It is true that WaitHandle.WaitAny() is not quite enough to match the functionality of WaitForMultipleObjects(). But you just need to use WaitHandle.WaitAll() as well.

WaitHandle.WaitAny() matches WaitForMultipleObjects() called with the WaitAll parameter set to FALSE,.
WaitHandle.WaitAll() matches it with WaitAll set to TRUE.

score 3 · Answer 2 · answered Sep 15 '11 at 13:08

Pretty the same signature and behaviour, so it is a good candidate. If WaitForMultipleObjects() was called with WaitAll=true you could use WaitHandle.WaitAll() as well

C++ WaitForMultipleObjects()

DWORD WINAPI WaitForMultipleObjects(
  __in  DWORD nCount,
  __in  const HANDLE *lpHandles,
  __in  BOOL bWaitAll,
  __in  DWORD dwMilliseconds
);

Waits until one or all of the specified objects are in the signaled state or the time-out interval elapses

C# WaitHandle.WaitAny()

public static int WaitAny(
    WaitHandle[] waitHandles,
    TimeSpan timeout,
    bool exitContext
)

Waits for any of the elements in the specified array to receive a signal, using a TimeSpan to specify the time interval and specifying whether to exit the synchronization domain before the wait.

.NET provides an other method WaitHandle.WaitAll() but it usefull when you need to ensure that ALL handles are received a signal.

score 2 · Answer 3 · answered Sep 15 '11 at 16:29

It is fine, it uses WaitForMultipleObjects() under the hood. Which you can find out with this little test program:

using System;
using System.Threading;

class Program {
    static void Main(string[] args) {
        var waits = new WaitHandle[65];
        for (int ix = 0; ix < waits.Length; ++ix) waits[ix] = new ManualResetEvent(false);
        WaitHandle.WaitAny(waits);
    }
}

Same restriction that WaitForMultipleObjects has. The WaitMultiple() method is marked MethodImplOptions.InternalCall because it actually lives inside the CLR. Which wants to know about blocking waits in order to provide several managed threading guarantees. Like pumping a message loop on a UI thread to keep COM happy (MsgWaitForMultipleObjects), knowing when a remoting request can be suspended for the next request and knowing when a thread is in a safe state to honor abort requests.

WaitHandle.WaitAny to match WaitForMultipleObjects functionality

3 Answers3

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