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  1. JBRULES
  2. JBRULES-541

Avoid WeakHashmap for tracking working memories in a RuleBase.

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      Description

      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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          Attachments

          1. Engine.java
            1 kB
          2. MultiThreadTest.java
            0.8 kB
          3. rules.drl
            0.1 kB

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                • Assignee:
                  mark.proctor Mark Proctor
                  Reporter:
                  michaelneale Michael Neale
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                  • Created:
                    Updated:
                    Resolved: