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copied!<p>Depending on what you are doing with the files (you say disk based caching so I assume reads as well as writes) then I would suggest trying something based upon <a href="http://msdn.microsoft.com/en-us/library/sb7kah3h.aspx" rel="nofollow">ReaderWriterLock</a>, if you can upgrade to .Net 3.5 then try <a href="http://msdn.microsoft.com/en-us/library/system.threading.readerwriterlockslim%28v=VS.90%29.aspx" rel="nofollow">ReaderWriterLockSlim</a> instead as it performs much better.</p> <p>As a general step to reducing the potential endless recursion case in your example change the first bit of the code to the following:</p> <pre><code>do { // 1) Creation/aquire phase lock (createLock){ // We have to lock on dictionary writes, since otherwise // two locks for the same file could be created and assigned // at the same time. (i.e, between TryGetValue and the assignment) if (!locks.TryGetValue(key, out itemLock)) locks[key] = itemLock = new Object(); //make a new lock! } // Loophole (part 1): // Right here - this is where another thread could remove 'itemLock' // from the dictionary, and potentially, yet another thread could // insert a new value for 'itemLock' into the dictionary... etc, etc.. // 2) Execute phase lock(itemLock){ // May take minutes to acquire this lock. // Real version would specify a timeout and a failure callback. // Trying to detect an occurence of loophole above // Check that itemLock still exists and matches the dictionary lock(createLock){ object newLock = null; validLock = locks.TryGetValue(key, out newLock); validLock = validLock && newLock == itemLock; } // Only run the callback if the lock is valid if (validLock) callback(); // Extremely long-running callback. } // If we had an invalid lock, we have to try everything over again. } while (!validLock); </code></pre> <p>This replaces your recursion with a loop which avoids any chance of a StackOverflow by endless recursion.</p>

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