Is ReaderWriterLockSlim resistant to ThreadAbortException?

Question

I would like to check whether following code is resistant against ThreadAbortException and will not lead into orphan lock. If it is not, what is the best pattern to avoid orphan locks here?

ReaderWriterLockSlim _lock = new ReaderWriterLockSlim();

public void DoStaff()
{
  _lock.EnterWriteLock();
  //Is this place where ThreadAbotException can corrupt my code, or is there JIT optimalization which prevent this from happening??? 
  try
  {
    ...
  }
  finally
  {
    _lock.ExitWriteLock();
  }
}

According following link http://chabster.blogspot.cz/2013/07/a-story-of-orphaned-readerwriterlockslim.html, there is (or at least there was) possible way how to create orphan locks but I was running sample code for a while without any luck.

I am using .NET 4.0

Is there any difference between behavior in Debug and Release?

Answer 1

Yes, ThreadAbortException could occur there, in which case the try wouldn't be entered and therefore you would never exit the write lock.

There's no good general solution to the problem. Which is why Eric Lippert (among others) says that Locks and exceptions do not mix.

You're asking specifically about ThreadAbortException, which leads me to believe that you're contemplating using Thread.Abort for some kind of threading control in your application. I urge you to reconsider. If you want the ability to cancel your threads, you should use Cancellation or something similar. Using Thread.Abort in any other than the most dire circumstances is a horrifically bad idea. It certainly should not be part of your program's overall design.

Answer 2

In order for code which uses a locking primitive to be robust in the face of thread aborts, it is necessary that every lock-acquisition and lock-release request pass, or be performed through, an unshared token which can be given "ownership" the lock. Depending upon the design of the locking API, the token may be an object of some specific type, an arbitrary Object, or a variable passed as a ref parameter. It's imperative, however, that the token be created and stored by some means before the lock is acquired, so that if the token gets created but the store fails, the token may be abandoned without difficulty. Unfortunately, although monitor locks have added (in .NET 4.0) overloads of Monitor.Enter and Monitor.TryEnter which use ref bool as a token, I know of no equivalent for reader-writer locks.

If one wants abort-safe reader-writer lock functionality, I would suggest one would need a class which was designed around that; it should keep track of what threads hold reader or writer access and, rather than relying upon threads to release locks, it should, when waiting for a lock to be released, make sure the thread holding it is still alive. If a thread dies while holding read access, it should be released. If a thread dies while holding right access, any pending or future attempts to acquire the lock should throw an immediate exception.

Otherwise, there are some tricks via which a block of code can be protected against Thread.Abort(). Unfortunately, I don't know any clean way to bracket the code around a lock-acquisition request in such a way that Abort will work when the request itself can be cleanly aborted without having succeeded, but will be deferred if the request succeeds.

There are ways via which a framework could safely allow a thread which is in an endless loop to be killed by another thread, but designing mechanisms which could be used safely would require more effort than was put into Thread.Abort().