[jboss-jira] [JBoss JIRA] Created: (JBRULES-541) Avoid WeakHashmap for tracking working memories in a RuleBase.

[Michael Neale (JIRA)]

Avoid WeakHashmap for tracking working memories in a RuleBase.
--------------------------------------------------------------

                 Key: JBRULES-541
                 URL: http://jira.jboss.com/jira/browse/JBRULES-541
             Project: JBoss Rules
          Issue Type: Feature Request
      Security Level: Public (Everyone can see)
          Components: Rule Assemply/SPI
    Affects Versions: 3.0.4
            Reporter: Michael Neale
         Assigned To: Mark Proctor
            Priority: Critical


This comes under the heading of "I knew it would happen one day and I warned people about it but they didn't listen and Michael is always right in the long run, except when he predicted that the graphical web browser would NOT take off back in 1993 and was catastrophically wrong.

Someone was having issues with concurrency (5 concurrent threads, but heavy load) and creating a newWorkingMemory - there are hangs/lock issues with the weak hashmap that points from the Single rule base to the spawned working memories. This is not surprising, blah blah blah....

Anyway, one possible solution is to have a call where users who *want* to update an existing long lived working memory changes, pass in the WM to the rulebase, with say "refresh rules" - ie the methods like removeRule() on a rule base, require a working memory to be passed in.

We can still keep the old WeakHashMap, just make it non default behaviour (it cannot scale the way it is now - with the default behaviour in my opinion). 

STACK trace follows:

I'm using Java 1.5_09 on Linux. The app uses 5 simultaneous threads at
the moment. They never share WorkingMemory instances but do share the
same RuleBase.

A thread dump (see below) shows all threads being stuck in
java.util.WeakHashMap, which is called from
AbstractRuleBase.addWorkingMemory.

Has anyone seen this before? I attempted to synchronize the method
that's the entry point to newWorkingMemory(). That definitely made the
problem happen less often but didn't solve it completely. Anyone knows
any other workarounds?
Thanks,
Per

"CW4" prio=1 tid=0x1a4fd7a8 nid=0xc44 runnable [0x1a2fe000..0x1a2fefb0]
       at
java.util.WeakHashMap.expungeStaleEntries(WeakHashMap.java:289)
       at java.util.WeakHashMap.getTable(WeakHashMap.java:297)
       at java.util.WeakHashMap.put(WeakHashMap.java:394)
       at org.drools.common.AbstractRuleBase.addWorkingMemory(Unknown
Source)
       at org.drools.reteoo.ReteooRuleBase.newWorkingMemory(Unknown
Source)
       at org.drools.common.AbstractRuleBase.newWorkingMemory(Unknown
Source)

"CW3" prio=1 tid=0x1a4fd5f0 nid=0xc43 runnable [0x1a6fe000..0x1a6fee30]
       at java.util.WeakHashMap.put(WeakHashMap.java:397)
       at org.drools.common.AbstractRuleBase.addWorkingMemory(Unknown
Source)
       at org.drools.reteoo.ReteooRuleBase.newWorkingMemory(Unknown
Source)
       at org.drools.common.AbstractRuleBase.newWorkingMemory(Unknown
Source)

"CW2" prio=1 tid=0x1a4fd100 nid=0xc42 runnable [0x1a8e5000..0x1a8e5eb0]
       at
java.util.WeakHashMap.expungeStaleEntries(WeakHashMap.java:289)
       at java.util.WeakHashMap.getTable(WeakHashMap.java:297)
       at java.util.WeakHashMap.put(WeakHashMap.java:394)
       at org.drools.common.AbstractRuleBase.addWorkingMemory(Unknown
Source)
       at org.drools.reteoo.ReteooRuleBase.newWorkingMemory(Unknown
Source)
       at org.drools.common.AbstractRuleBase.newWorkingMemory(Unknown
Source)

"CW1" prio=1 tid=0x19afca78 nid=0xc41 runnable [0x1a966000..0x1a967130]
       at
java.util.WeakHashMap.expungeStaleEntries(WeakHashMap.java:289)
       at java.util.WeakHashMap.getTable(WeakHashMap.java:297)
       at java.util.WeakHashMap.put(WeakHashMap.java:394)
       at org.drools.common.AbstractRuleBase.addWorkingMemory(Unknown
Source)
       at org.drools.reteoo.ReteooRuleBase.newWorkingMemory(Unknown
Source)
       at org.drools.common.AbstractRuleBase.newWorkingMemory(Unknown
Source)
       at

"CW0" prio=1 tid=0x19afc7d8 nid=0xc40 runnable [0x1aafe000..0x1aaff1b0]
       at
java.util.WeakHashMap.expungeStaleEntries(WeakHashMap.java:289)
       at java.util.WeakHashMap.getTable(WeakHashMap.java:297)
       at java.util.WeakHashMap.put(WeakHashMap.java:394)
       at org.drools.common.AbstractRuleBase.addWorkingMemory(Unknown
Source)
       at org.drools.reteoo.ReteooRuleBase.newWorkingMemory(Unknown
Source)
       at org.drools.common.AbstractRuleBase.newWorkingMemory(Unknown
Source)
       at

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