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copied!<p>I have not used AspectJ so cannot vouch for how easy it is to use. I have used <a href="http://asm.ow2.org" rel="nofollow">ASM</a> to create a custom code profiler, this was about 2 days work. The effort to instrument synchronization should be similar. AspectJ should be quicker and easier once you are up to speed with aspects.</p> <p>I have implemented deadlock detecting trace for our c++ based server. Here is how I did it:</p> <ul> <li>When ever acquiring or releasing a lock I traced: <ul> <li><code><time> <tid> <lockid> <acquiring|releasing> <location in code></code></li> </ul></li> <li>This extra trace affected performance quite drastically and was not usable in production.</li> <li>So when a possible deadlock was discovered in production I used the log file to figure out what was happening around the deadlock. Then reproduced this functionality in a test environment with my tracing turned on.</li> <li>Then I ran a script on the log file to see if deadlock was possible and how. I used an awk script, using this algoritm: <ul> <li>Foreach line <ul> <li>if acquiring <ul> <li>add lockid to list of current locks for this thread</li> <li>add each pair of locks in this list to a set lock pairs for this thread. eg for list of <code>Lock A -> Lock B -> Lock C</code> generate the pairs <code>(Lock A, Lock B), (Lock A, Lock C), (Lock B, Lock C)</code></li> </ul></li> <li>if releasing <ul> <li>remove current lockid from tail of list for this thread</li> </ul></li> </ul></li> <li>For each lock pair search all other threads for the reverse lock pairs, each match is a potential deadlock so print the pairs and threads affected</li> <li>Instead of making the algorithm smarter I then desk checked that the lock acquisition to see if it was a real deadlock.</li> </ul></li> </ul> <p>I did this after failing to find the cause of a deadlock for a number of days, it took a few more days to implement and a few hours to find the deadlock.</p> <p>If you are considering this approach in Java things to consider are:</p> <ul> <li>Do you only use <code>synchronized</code> to protect your critical sections? Are you using the classes in java.lang.concurrent? (these might require special handling/instrumentation)</li> <li>How easy is it to print the code location with aspects/ASM? I used <code>__FILE__</code> and <code>__LINE__</code> in c++. ASM will give you the class name, method name and signature.</li> <li>You cannot instrument the locks used to protect your tracing/logging.</li> <li>You can streamline your instrumentation if you use a log file per thread and thread local storage for the file object.</li> <li>How do you uniquely identify objects you synchronize on? Maybe toString() and System.identityHashCode() would be enough, but might require more. I used the address of the object in C++.</li> </ul>

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