.NET 4 equivalent of Task.WhenAll()

问题:

In .NET 4, is there any functional equivalent to .NET 4.5's System.Threading.Tasks.Task.WhenAll()?

The goal is to wrap up multiple async tasks into a single one that is completed when all of its constituent tasks are done.

回答1:

I think the closest thing built-in in .Net 4.0 is ContinueWhenAll(). You can make the continuationAction a simple tasks => tasks and use the returned Task.

For performance reasons, you might want to use it with TaskContinuationOptions.ExecuteSynchronously.

回答2:

In .NET Framework 4.0 WhenAll and WhenAny can be used with installed AsyncCTP in case of Visual Studio 2010 or Async Targeting Pack in case of Visual Studio 2012.

The WhenAll and WhenAny methods are then offered on the TaskEx type.

回答3:

Try waiting on Task.WaitAll() in another Task. Use the LINQ extension method ToArray to convert from IEnumerable<Task> to Task[].

Task WhenAll(IEnumerable<Task> tasks)
{
    return Task.Factory.StartNew(() => Task.WaitAll(tasks.ToArray()));
}