Can you call Wait() on a task multiple times?

问题:

I want to run initializations of some objects asynchronously, but some objects depend on others being initialized. And then all objects need to be initialized before the rest of my application continues.

Is it possible to call Wait() on a task and later call Wait() on it again, or as in my example WaitAll() on a collection where it is included?

Dictionary<String, Task> taskdict = new Dictionary<String, Task>( );

   taskdict.Add( "Task1",
        Task.Factory.StartNew( ( ) => {
         //Do stuff
        } ) );

   taskdict.Add( "Task2",
        Task.Factory.StartNew( ( ) => {
          taskdict[ "Task1" ].Wait( );

         //Do stuff

        } ) );

      try {
        Task.WaitAll( taskdict.Values.Convert<Task[ ]>( ) );
      }

Or will that second Wait() / WaitAll() fail?

回答1:

You most certainly can wait on a task twice. You can wait on a task as many times as you want with no negative side effects. Now, if you've already waited on a task in that same thread it will already be done, so the future Wait calls will all just return immediately as there is nothing to wait for, but they certainly won't fail or otherwise produce inappropriate results.

Note that if a task didn't complete normally and was instead cancelled or couldn't finish as a result of an exception being thrown then calling Wait will re-throw the exception (each time you call Wait). If Wait is throwing exceptions for you, there's a chance that that is the reason.