.NET Reverse Semaphore?

Question

Perhaps it\'s too late at night, but I can\'t think of a nice way to do this.

I\'ve started a bunch of asynchronous downloads, and I want to wait until they all comp

Answer 1

In .NET 4 there is a special type for that purpose CountdownEvent.

Or you can build similar thing yourself like this:

const int workItemsCount = 10;
// Set remaining work items count to initial work items count
int remainingWorkItems = workItemsCount;

using (var countDownEvent = new ManualResetEvent(false))
{
    for (int i = 0; i < workItemsCount; i++)
    {
        ThreadPool.QueueUserWorkItem(delegate
                                        {
                                            // Work item body
                                            // At the end signal event
                                            if (Interlocked.Decrement(ref remainingWorkItems) == 0)
                                                countDownEvent.Set();
                                        });
    }
    // Wait for all work items to complete
    countDownEvent.WaitOne();
}