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Deadlock detector

If a Java-level deadlock happens in the profiled application, it will be automatically detected.

When you are connected to the profiled application, switch to the "Deadlocks" tab.

deadlocks tab

If the deadlock is found, a notification will be shown. Find the deadlock detail in the "Deadlocks" tab.

deadlock detected

Potential deadlocks

The profile can detect deadlocks which are not otherwise reported by standard Java mechanism which detects only Java-level deadlocks, but does not detect deadlocks of Java threads caused by JVM internal locks (e.g. class loader) or native methods which explicitly use low-level synchronization primitives.

An heuristics detects threads whose stack does not changed for some period of time, which is a sign of potential deadlock or hung thread.

potential deadlock

Well-known cases when thread can legally stay in same state for a long time are excluded. In particular, it can be threads which are waiting for incoming connection in ServerSocket.accept(), some JVM internal threads etc.

Important: the potential deadlock detection depends on thread stack telemetry. If thread state telemetry is stopped, the detection is not possible.

Potential deadlocks are not necessarily actual deadlocks. It is possible that the reported threads are performing the same operation for a long time, and will eventually finish. Use Refresh button to check if detected threads are still considered frozen.

For each potentially deadlocked or hanged thread there is a link to ignore it. Once ignored, the stack will no longer be reported as a potential deadlock.

ignore deadlock

Ignored false positive deadlocks are stored in the file<user home>/.yjp/deadlock_ignore_list.json. This file can also be edited manually or deleted to reset to defaults. Manual changes to the file are applied on the profiler UI restart.

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