How to Detect and Fix Automatic Lock Release That Triggers Duplicate Execution

In distributed or multi‑threaded Java applications, a lock may be automatically released (for example, after a timeout), which can lead to the same business logic being executed more than once.

To discover this problem, monitor your logs or metrics for repeated execution of the critical section and verify whether the lock was released prematurely.

One practical solution is to replace explicit Lock usage with the built‑in synchronized keyword. Since JDK 1.6, the performance gap between synchronized and Lock is minimal because the JVM has optimized synchronized with techniques such as spin‑locks, adaptive spinning, biased locking, and lightweight locking. The synchronized block is implemented via monitorenter and monitorexit, and a synchronized method carries the ACC_SYNCHRONIZED flag.

In a distributed environment, consider using a dedicated coordination service such as etcd, which provides automatic lock renewal and other safety features.

If the lock timeout causes automatic release, you can enable lock renewal mechanisms—for instance, Redisson’s watchdog feature—or design your business logic to be idempotent so that repeated execution does not cause incorrect results.