Deadlock in Cocoon leads to server crash
----------------------------------------
Key: COCOON-2261
URL: https://issues.apache.org/jira/browse/COCOON-2261
Project: Cocoon
Issue Type: Bug
Components: * Cocoon Core
Affects Versions: 2.1.11
Reporter: neeru mhatre
Fix For: 2.1.11
The DEADLOCK scenario:
======================
Inside Cocoon's FOM_JavaScriptInterpreter.java we have the following two
methods:
Method 1 called by [ACTIVE] ExecuteThread: '5'
org.apache.cocoon.components.flow.javascript.fom.FOM_JavaScriptInterpreter.han
dleContinuation(FOM_JavaScriptInterpreter.java:850)
------------------------------------------------
handleContinuation() {
.................
ThreadScope kScope = (ThreadScope)k.getParentScope();
synchronized (kScope) { -> LOCK A [Blocks on 0xbbb26dd8 (kScope)]
...............
} finally {
....................
setSessionScope(kScope); -> LOCK B [Blocks on 0xbd197028
"AttributeWrapper for kScope" with the call AttributeWrapper.getObject() ->
LOCK A [Blocks on 0xbbb26dd8 (kScope) with the call
ScriptableObject.writeObject() <ThreadScope isA ScriptableObject>]]
.............
}
}
}
.
.
Method 2 called by [ACTIVE] ExecuteThread: '4'
org.apache.cocoon.components.flow.javascript.fom.FOM_JavaScriptInterpreter.cal
lFunction(FOM_JavaScriptInterpreter.java:711)
-----------------------------------------------
callFunction() {
.....................
ThreadScope thrScope = getSessionScope(); -> LOCK B [Blocks on 0xbd197028
"AttributeWrapper for thrScope == kScope" -> LOCK A [Blocks on 0xbbb26dd8
(thrScope == kScope) with the call ScriptableObject.writeObject()
<ThreadScope isA ScriptableObject>]]
synchronized (thrScope) { -> LOCK A [Blocks on 0xbbb26dd8 (kScope)]
..............
}
}
To summarize we have:
[ACTIVE] ExecuteThread: '5' LOCK A, LOCK B, LOCK A
[ACTIVE] ExecuteThread: '4' LOCK B, LOCK A, LOCK A
which leads to a deadlock. Eventually, this causes a server to crash.
This is causing serious problems on a production server, causing unavailability
of server.
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