What are Locked Threads?

The Plumbr Agent monitors all JVM threads for lock contention events. Plumbr monitors both synchronized block/method access and java.util.concurrent locks.

For synchronized blocks/methods, Plumbr tracks the situations where a thread in the JVM executes code in a synchronized block or method and another thread tries to enter the same synchronized block/method.

For java.util.concurrent locks Plumbr will detect the situations where threads are forced to wait for events originating from the use of various java.util.concurrent classes, ranging from ReentrantLock to ArrayBlockingQueue.

When the wait times in either of the case exceeds a predetermined threshold, the root cause will be exposed, containing the following:

• How long the thread was forced to wait before getting access to the synchronized block/method.
• The monitor used to lock the method/code block (for synchronized usage only).
• The name and call stack from the thread trying to enter the synchronized block/method.
• The name and a snapshot of the call stack of the thread whose code was running in the synchronized block. The snapshot of the call stack is taken when the waiting time for the blocked thread is about to exceed the configured threshold.

Having such information allows you to zoom in to the underlying root cause with the precision of a single line in the source code, skipping the tedious and complex process of troubleshooting concurrency issues. Notice that Plumbr also binds together similar lock contention events, allowing you to rank the severity of the performance issues based on the frequency of the underlying root cause.