分析Java死锁:分析jstack日志(八)
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This is the status of the thread; in this case it’s BLOCKED. Also included is a stack trace outlining where the thread is blocked.
Note that a thread can also be marked as a daemon. For example:
"RMI TCP Accept-0" daemon prio=5 tid=7f97128fd800 nid=0x117837000 runnable [117836000]
java.lang.Thread.State: RUNNABLE
Daemon threads are background task threads such as the RMI TCP Accept-0 thread listed above. A daemon thread is a thread that does not prevent the JVM from exiting. The JVM will exit, or close down, when only daemon threads remain.
However, the thread list doesn't really help in tracing the cause of a deadlock, so moving swiftly along...
The Deadlock Thread List
This section of the thread dump contains a list of all threads that are involved in the deadlock.
Found one Java-level deadlock:
=============================
"Thread-21":
waiting to lock monitor 7f97118bd560 (object 7f3366f58, a threads.deadlock.Account),
which is held by "Thread-20"
"Thread-20":
waiting to lock monitor 7f97118bc108 (object 7f3366e98, a threads.deadlock.Account),
which is held by "Thread-4"
"Thread-4":
waiting to lock monitor 7f9711834360 (object 7f3366e80, a threads.deadlock.Account),
which is held by "Thread-7"
"Thread-7":
waiting to lock monitor 7f97118b9708 (object 7f3366eb0, a threads.deadlock.Account),
which is held by "Thread-11"
"Thread-11":
waiting to lock monitor 7f97118bd560 (object 7f3366f58, a threads.deadlock.Account),
which is held by "Thread-20"
From the segment above, you can see that there are five threads all blocking on instances thethreads.deadlock.Account class
Leaving aside the monitor ids and Account instances, you can see that "Thread-21" is waiting for "Thread-20", which is waiting for "Thread-4", which in turn is waiting for "Thread-7". "Thread-7" is waiting for "Thread-11", which is waiting for "Thread-20": a deadlock loop as shown in the diagram below:
The Deadlock Stack Traces
The final piece of the puzzle is the list of deadlocked thread stack traces as shown below:
Java stack information for the threads listed above:
===================================================
"Thread-21":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366f58> (a threads.deadlock.Account)
- locked <7f3366ee0> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-20":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e98> (a threads.deadlock.Account)
- locked <7f3366f58> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-4":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366e80> (a threads.deadlock.Account)
- locked <7f3366e98> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTransferOperation.run(DeadlockDemo.java:59)
"Thread-7":
at threads.deadlock.DeadlockDemo$BadTransferOperation.transfer(DeadlockDemo.java:86)
- waiting to lock <7f3366eb0> (a threads.deadlock.Account)
- locked <7f3366e80> (a threads.deadlock.Account)
at threads.deadlock.DeadlockDemo$BadTrans