Do I Need to Dispose of Tasks in Fire-and-Forget Background Operations?

Is Task Disposal Necessary for Fire-and-Forget Background Tasks?

When performing fire-and-forget tasks on background threads, developers often utilize the Task Parallel Library (TPL) method Task.Factory.StartNew(). This method returns a Task object, raising concerns about proper disposal.

msdn documentation suggests calling Dispose() before releasing the last reference to a Task. However, waiting for task completion to invoke this method negates the purpose of background execution.

Discussion

According to Stephen Toub of the Microsoft pfx team, a Task object may wrap an event handle when waiting on its completion. However, if continuations are utilized, this handle is never allocated. Therefore, finalization is an adequate method of cleanup.

Update (October 2012)

Toub's blog post "Do I Need to Dispose of Tasks?" provides further clarification. In .NET 4.5, a Task only allocates the internal wait handle when AsyncWaitHandle is explicitly used. Furthermore, Task does not have a finalizer; any allocated handle is wrapped in an object with a finalizer. This means that disposing of most Task objects is unnecessary.

Conclusions

In most cases, it is acceptable to refrain from calling Dispose() on Task objects used for fire-and-forget background tasks. Finalization will typically suffice for resource cleanup. However, if AsyncWaitHandle is utilized or the application experiences heavy reliance on such tasks, explicit disposal may be warranted.

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