DeadlockDetector class allows you to programmatically detect basic deadlocks in your Java code. You can output deadlocks using the following code (note that printing a thread dump using the
ThreadDump class will automatically attempt to find any deadlocks).
There are various types of deadlock in concurrent systems, broadly speaking with regard to Java, they can be categorised as
- Java monitor cyclic locking dependency
Lockcyclic locking dependency
- External resource based dependency
- Live lock
DeadlockDecector class can only spot Java monitor cyclic locking problems. It's implementation is basically the same as that used by
jstack and suffers the same limitations. Java 1.6 versions of
jconsole can additionally detect
Lock based cyclic problems. The types of deadlock it can detect can be illustrated in the example below.
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Kidnapper is unwilling to release poor Nibbles the
Cat until he has the
Cash but our
Negotiator is unwilling to part with the
Cash until he has poor Nibbles back in his arms. The deadlock detector displays this woeful situation as follows.
Deadlock detected ================= "Negotiator-Thread-1": waiting to lock Monitor of com.google.code.tempusfugit.concurrency.DeadlockDetectorTest$Cat@ce4a8a which is held by "Kidnapper-Thread-0" "Kidnapper-Thread-0": waiting to lock Monitor of com.google.code.tempusfugit.concurrency.DeadlockDetectorTest$Cash@7fc8b2 which is held by "Negotiator-Thread-1"