When a customer creates a plugin, for example a JDBCListener, there exists the possibility for the custom JDBCListener to retain a reference to a Classloader, which in turn will not allow the Classloader to be GC'd. For example, when the JDBCListener is part of a JEE application and the application is restarted, the JDBCListener class can be listed as as a leak suspect, as follows in this leak suspect stack:
75,675,296 (59.45%) [32] 67 class org/apache/openjpa/kernel/AbstractBrokerFactory 0x1027f7e8
- 75,637,832 (59.42%) [32] 40 class org/apache/openjpa/lib/conf/Configurations 0xf370b48
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- 75,637,552 (59.42%) [64] 2 org/apache/openjpa/lib/util/concurrent/ConcurrentReferenceHashMap 0x1110fa40
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- 75,637,464 (59.42%) [64] 3 array of org/apache/openjpa/lib/util/concurrent/ConcurrentReferenceHashMap$Entry 0x11115620
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- 75,514,544 (59.32%) [48] 4 org/apache/openjpa/lib/util/concurrent/ConcurrentReferenceHashMap$WeakEntry 0x1111edb0
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- 75,514,496 (59.32%) [48] 1 java/util/concurrent/ConcurrentHashMap 0x111f47b8
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- 75,514,448 (59.32%) [80] 16 array of java/util/concurrent/ConcurrentHashMap$Segment 0x111f47e8
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- 75,505,976 (59.32%) [32] 2 java/util/concurrent/ConcurrentHashMap$Segment 0x111f48d0
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- 75,505,912 (59.32%) [24] 1 array of java/util/concurrent/ConcurrentHashMap$HashEntry 0x110d8f08
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- 75,505,888 (59.32%) [24] 2 java/util/concurrent/ConcurrentHashMap$HashEntry 0x110d8f18
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- 75,505,752 (59.32%) [32] 18 class listener/MyJDBCListener 0x10296078
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- 75,505,600 (59.31%) [48] 1 java/util/HashMap 0x11113f88
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- 75,505,552 (59.31%) [65,552] 6,411 array of java/util/HashMap$Entry 0x1401ed10
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As can be seen in this stack, my JDBCListener (class MyJDBCListener) is part of the leak suspect, with a retained Configurations class. When looking at the Configurations class, it can be seen that the Configurations class has a ConcurrentReferenceHashMap which contains a Classloader to Map, where the Map contains the JDBCListener class (MyJDBCListener). It is these two maps which causes the leak.
Thanks,
Heath
Minor