Should I Dispose of Task Objects in the TPL?

Understanding the Need for Task Disposal in TPL

When working with the Task Parallel Library (TPL) to initiate background tasks without waiting for their completion, the question arises whether disposing of the returned Task object is essential. This article aims to address this concern and explore the implications of not calling the Dispose() method.

Task Object and Its IDisposable Implementation

In TPL, the StartNew() method returns a Task object which implements the IDisposable interface. The MSDN documentation for Task.Dispose() states the importance of calling Dispose before releasing the last reference to the Task.

Concerns Regarding Unmanaged Resource Allocation

One concern is that the Task object might allocate unmanaged resources, such as wait handles, which need to be released explicitly through Dispose() to avoid memory leaks. However, Stephen Toub, a member of the Microsoft pfx team, clarifies that this scenario is unlikely.

According to Toub, Task objects only allocate an event handle when waiting on them requires blocking (rather than spinning or executing the waiting task). In the case of using continuations, this event handle is never allocated.

Finalization as a Fallback

If not called explicitly, the finalizer will eventually reclaim any unmanaged resources associated with a Task object. However, relying on finalization may not be ideal, especially when handling a large volume of fire-and-forget tasks, as it can overwhelm the finalizer thread.

Recommendations

In summary, the general consensus is that disposing of Task objects is not typically necessary in most scenarios. The following recommendations provide guidance:

• If your code explicitly uses the AsyncWaitHandle property of the Task object, you should dispose of the Task to release the unmanaged wait handle.
• In all other cases, relying on finalization is generally sufficient, even when dealing with a substantial number of fire-and-forget tasks.

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