2:13 p.m.
[
https://jira.jboss.org/jira/browse/JBRULES-1876?page=com.atlassian.jira.p...
]
Shahad Ahmed updated JBRULES-1876:
----------------------------------
Attachment: deadlock.zip
I've been able to reproduce the deadlock with 5.0.0-M4.
I've attached the file deadlock.zip that contains a modified version of the drools
"Hello World" example. This loads rules via a RuleAgent and then repeatedly
fires the rules for a minute, with the rule refresh polling set to 5 seconds. I can
reproduce the deadlock once in every 4 or 5 test runs, where a test run is as follows:
1. Run the DroolsAgentTest application.
2. Once you start seeing the "Hello World" messages on the console, modify the
SampleAgent.drl file by commenting out the println in the "Hello World" Rule and
save the file, i.e. modify as follows: //System.out.println( message ). This changes the
rules file so that the polling will refresh the rules.
3. The output should stop printing "Hello World" and only show "Goodbye
cruel world". However, occasionally a deadlock happens and the output does not change
and the just hangs.
4. Note that if you do not get a deadlock once you save the modified rules file then
remove the modification (i.e. remove the //) and save and see if it deadlocks. I sometimes
have to modify and change the rules file a few times during the 1 minute run to get the
deadlock. Note that the length of the run can be increase from a minute by changing the
TEST_PERIOD value in the test class, in case you need more time to modify the rules file
during a run.
Deadlock when RuleAgent thread refreshes rules while another thread
creates a statefulSession
---------------------------------------------------------------------------------------------
Key: JBRULES-1876
URL: https://jira.jboss.org/jira/browse/JBRULES-1876
Project: JBoss Drools
Issue Type: Bug
Security Level: Public(Everyone can see)
Components: drools-core
Affects Versions: 4.0.7
Environment: Windows XP SP3
Sun JRE 1.5.0_14
Reporter: Shahad Ahmed
Assignee: Michael Neale
Attachments: deadlock.zip
I believe I have discovered a deadlock that can occur in drools 4.0.7 if the RuleAgent
refreshes its associated RuleBase whilst a new stateful session is being created on the
RuleBase by another thread.
The thread dump below shows the deadlock where the two thread "Timer-15" and
"DataSource(com.acme.Source)-2" are deadlocked. Thread "Timer-15" is
the timer thread created by the RuleAgent rule refresh mechanism to check if the rules
files have changed, and to refresh the rules when a change is found. If it finds changes
to the rules then it obtains a lock (<0x189a8d88> (a java.util.HashMap)) and
proceeds to removes the old version of the changed package from the RuleBase. To do this
it needs to obtain another lock (<0x189a2ba0> (a org.drools.reteoo.ReteooRuleBase))
before it can call removeRule.
However, in another thread "DataSource(com.acme.Source)-2" a new stateful
session is being created on the same RuleBase. This has already obtained the lock
(<0x189a8d88> (a java.util.HashMap)) that the Timer thread is waiting for, and is
itself waiting for the another lock <0x189a2ba0> (a
org.drools.reteoo.ReteooRuleBase) that the Timer thread has already locked, hence the
deadlock.
In my own application I coded around this by eventually not using the RuleAgent in-built
refresh mechanism, but instead periodically calling refreshRuleBase() on the RuleAgent in
the SAME thread used to create the Stateful session, thus avoiding any deadlock.
"Timer-15" daemon prio=6 tid=0x02f4b0e8 nid=0x1864 waiting for monitor entry
[0x038cf000..0x038cfa68]
at org.drools.reteoo.ReteooRuleBase.removeRule(ReteooRuleBase.java:270)
- waiting to lock <0x189a2ba0> (a org.drools.reteoo.ReteooRuleBase)
at org.drools.common.AbstractRuleBase.removeRule(AbstractRuleBase.java:656)
at org.drools.common.AbstractRuleBase.removePackage(AbstractRuleBase.java:570)
- locked <0x189a8d88> (a java.util.HashMap)
at org.drools.agent.PackageProvider.removePackage(PackageProvider.java:45)
at org.drools.agent.PackageProvider.applyChanges(PackageProvider.java:63)
at org.drools.agent.RuleAgent.refreshRuleBase(RuleAgent.java:320)
at org.drools.agent.RuleAgent$2.run(RuleAgent.java:438)
at java.util.TimerThread.mainLoop(Unknown Source)
at java.util.TimerThread.run(Unknown Source)
"DataSource(com.acme.Source)-2" daemon prio=4 tid=0x03027610 nid=0xfac waiting
for monitor entry [0x0378f000..0x0378fb68]
at org.drools.reteoo.ReteooRuleBase.newStatefulSession(ReteooRuleBase.java:225)
- waiting to lock <0x189a8d88> (a java.util.HashMap)
- locked <0x189a2ba0> (a org.drools.reteoo.ReteooRuleBase)
at org.drools.common.AbstractRuleBase.newStatefulSession(AbstractRuleBase.java:284)
at com.acme.RunRules.flush(RunRules.java:3337)
at com.acme.ControlThread.run(ControlThread.java:465)
at java.lang.Thread.run(Unknown Source)
--
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators:
https://jira.jboss.org/jira/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira