Question

If I have the following block of code in a method (using .NET 4 and the Task Parallel Library):

var task = new Task(() => DoSomethingLongRunning());
task.Start();

and the method returns, will that task go out of scope and be garbage collected, or will it run to completion? I haven’t noticed any issues with GCing, but want to make sure I’m not setting myself up for a race condition with the GC.

Answer 1

Update:

After I answered this question (a long time ago!) I found out that it’s not true that Tasks will always run to completion – there’s a small, let’s say “corner” case, where tasks may not finish.

The reason for that is this: As I have answered previously, Tasks are essentially threads; but they are background threads. Background threads are automatically aborted when all foreground threads finish. So, if you don’t do anything with the task and the program ends, there’s a chance the task won’t complete.

You should always await on tasks. More information can be found on the excellent answer Jon gave me.

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Original:

Task are scheduled to the ThreadPool, meaning that they are essentially threads¹ (actually, they encapsulate threads).

From the Thread documentation:

It is not necessary to retain a
reference to a Thread object once you
have started the thread. The thread
continues to execute until the thread
procedure is complete.

So, no, there is no need to retain a reference to it.

Also, the documentation states that the preferred way to create a Task is to use it’s factory:

You can also use the StartNew method
to create and start a task in one
operation. This is the preferred way
to create and start tasks if creation
and scheduling do not have to be
separated (…)

Hope it helps.

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¹ Accordingly to the documentation:

A task represents an asynchronous
operation, and in some ways it
resembles the creation of a new thread
or ThreadPool work item, but at a
higher level of abstraction.