Should I Dispose() of Fire-and-Forget TPL Tasks?

Understanding the Need for Dispose() on TPL Tasks

When utilizing Task objects for fire-and-forget tasks, the question arises: Is it necessary to call Dispose()?

Background Thread Execution and Task.Dispose()

The Task Parallel Library (TPL) allows for the execution of tasks on background threads. Typically, StartNew() is used to create a Task object, which implements IDisposable. According to MSDN documentation, calling Dispose() before releasing the last reference to the Task is recommended.

Dilemma of Disposing Background Tasks

However, calling Dispose() requires the task to be completed, which defeats the purpose of using a background thread. Additionally, there is no completion event that can be used for cleanup.

Is It Acceptable to Not Dispose()?

According to Microsoft's Stephen Toub, in most cases, it is acceptable not to call Dispose() on Task objects used for continuations, as they will not allocate the internal wait handle. As of .Net 4.5, only explicit use of the AsyncWaitHandle will result in wait handle allocation.

Consequences and Risks

Toub notes that Task objects themselves do not have finalizers. The wait handle has a finalizer, but it is only allocated when necessary. Therefore, the finalizer will not be executed unless the wait handle is allocated.

However, in cases where many fire-and-forget tasks are being created, there is a potential for the finalizer thread to become overwhelmed if multiple wait handles are allocated.

Documentation and Best Practices

The MSDN page for the Task class does not explicitly address this issue. However, Stephen Toub's blog post, titled "Do I need to dispose of Tasks?", provides further clarification and recommends relying on finalization in most cases.

Alternative Approaches

If desired, there are ways to check for the availability of the wait handle and dispose of the Task if it has been allocated. Alternatively, one could explore other options for fire-and-forget tasks, such as the ThreadPool.QueueUserWorkItem method or using the Reactive Extensions for .NET (Rx).

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