Do I need to call Close() on a ManualResetEvent?
I've been reading up on .NET Threading and was working on some code that uses a ManualResetEvent. I have found lots of code samples on the internet. However, when reading the documentation for WaitHandle, I saw the following:
WaitHandle implements the Dispose pattern. See Implementing Finalize and Dispose to Clean Up Unmanaged Resources.
None of the samples seem to call .Close() on the ManualResetEvent objects they create, even the nice Recursion and Concurrency article from the pfxteam blog (Edit - this has a using block I has missed). Is this just example oversight, or not needed? I am curious because a WaitHandle "encapsulates operating system–specific objects," so there could easily be a resource leak.
Answer
I was recently forwarded an excerpt from C# 4.0 in a Nutshell: The Definitive Reference By Joseph Albahari, Ben Albahari. On page 834, in Chapter 21: Threading there is a section talking about this.
Disposing Wait Handles
Once you’ve finished with a wait handle, you can call its Close method to release the operating system resource. Alternatively, you can simply drop all references to the wait handle and allow the garbage collector to do the job for you sometime later (wait handles implement the disposal pattern whereby the finalizer calls Close). This is one of the few scenarios where relying on this backup is (arguably) acceptable, because wait handles have a light OS burden (asynchronous delegates rely on exactly this mechanism to release their IAsyncResult’s wait handle).
Wait handles are released automatically when an application domain unloads.