Measure thread contention on particular monitor

Question

I'm considering switching from synchronized to a ReadWriteLock. Before doing it, I would like to check if it's worth it.

ThreadMXBean and ThreadInfo provide information about overall thread blocked count and time. Those blocks can be caused by multiple monitors. Is there a way to measure block statistics given a particular monitor object?

Answer 1

Yes, it is possible using JVMTI.

What is you need is to write a native agent that handles a pair of events:

• MonitorContendedEnter - fired when a thread is about to enter syncrhonized block already acquired by another thread;
• MonitorContendedEntered - fired when a thread successfully acquires monitor after waiting.

Both events accept jthread and jobject arguments that correspond to a thread acquiring the monitor and the monitor object itself.

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Here is a sample code for the contention profiler agent.