In .Net, how can I do And/Or with Waithandles

Question

I have an array WaitHandle[], corresponding to tasks which all need to be completed before a thread can continue. But I also have another WaitHandle that gets signalled when a user requests an abort.

So what's the most efficient way to get a thread to wait until either:

1. All the WaitHandles in the array WaitHandle[] are signalled; OR

2. the user abort WaitHandle is signalled?

Answer 1

This is already provided in .NET 4 with the Task.WaitAll(Task[], CancellationToken) method so make sure that you are not trying to reinvent the wheel.

If you cannot move to .NET 4 for some reason or are too committed to existing code that doesn't use the Task class then you can implement something similar to what Task.WaitAll() does. The basic scheme is that you just work down the list of WaitHandles and wait one each one in turn, using WaitAny() so you can also see the abort request. Like this:

/// <summary>
/// Wait for all events with option to abort the wait
/// </summary>
/// <param name="waitHandles">Synchronization objects to wait for</param>
/// <param name="abortEvent">Event that signals an abort</param>
/// <returns>false if the wait was aborted</returns>
public static bool WaitAll(WaitHandle[] waitHandles, WaitHandle abortEvent) {
    WaitHandle[] pair = new WaitHandle[] { abortEvent, null };
    for (int ix = 0; ix < waitHandles.Length; ++ix) {
        pair[1] = waitHandles[ix];
        if (WaitHandle.WaitAny(pair) == 0) return false;
    }
    return true;
}

Answer 2

You can try WaitHandle.WaitAll()