WaitHandle.WaitAll和ManualResetEvent.Set（）-首先应该是什么？

Question

I have a question about working of WaitHandle.WaitAll, and would appreciate any help.

Let's assume I have such situation: the Parent thread is opening couple of Child Threads and must wait with 'doing other stuff' until child threads finish their work.

I use WaitHandle.WaitAll and would like to stay with this method. (NO Thread.Join etc, please :) )

ManualResetEvent[] events = new ManualResetEvent[list.Count];

foreach (string row in list)
{
    events[i] = new ManualResetEvent(false);                

    Thread thread = new Thread(new ParameterizedThreadStart(DoSomething));
    thread.Start(events[i]); // start child thread

    System.Threading.Thread.Sleep(1000000);

    i++;
}

WaitHandle.WaitAll(events); // wait for child threads finish their work
...
...


private DoSomething(object sth)
{
// some stuff that executes only 1 second
ManualResetEvent.Set()
}

So situation for the first newly started child-thread would be that the calling of ManualResetEvent.Set() is BEFORE calling WaitHandle.WaitAll(events) in the Parent thread. Because loop which opens new child threads has some long timeout.

So my question, wouldn't be such time-line a problem? Shouldn't be WaitHandle.WaitAll called before calling the ManualResetEvent.Set()?

Answer 1

It does not matter. The wait returns when all events are signaled (set) - whether or not that happened before or after wait was called.

Answer 2

As it was said, it does not matter, however, you should consider using the Task class for that kind of things.

It also allows you to run your tasks either simultaneously or consequentially.

Your code then will be only this:

Task.WaitAll(
    Task.Factory.StartNew(() =>
    {
        Thread.Sleep(1000);
    }),
    Task.Factory.StartNew(() => { Thread.Sleep(1000); }),
    Task.Factory.StartNew(() => { Thread.Sleep(1000); })
    );