Fix Jython memory leak #7
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Uses PhantomReferences to clean up after the interpreter
If the JythonScriptEngine or containing ScriptModule is set within the PythonInterpreter, we will get a circular reference chain preventing memory from the PythonInterpreter being reclaimed. To avoid completely discarding these objects, we can keep them in a shallow map to WeakReferences.
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@ctrueden - any objections here? |
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This is complex. I want to understand why it is necessary, so let's discuss a little before merging. |
Add extensive commenting to explain why PhantomReferences are needed to solve the memory leak identified in this implementation of the Python script language. Fixes http://fiji.sc/bugzilla/show_bug.cgi?id=1203
Pass a LogService to the thread polling the PhantomReference queue so that exceptions can be logged.
This isolates and encapsulates the cleanup logic, so the JythonScriptLanguage itself remains easy to understand.
This avoids them breaking the 80 character line limit, and makes them a little nicer to read (IMHO).
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Jython eval acts like an interpreter - any intermittently declared variables can be preserved. The PythonInterpreter is also frustratingly persistent and resists clean-up attempts.
This has led to a memory leak in our Jython script language (see http://fiji.sc/bugzilla/show_bug.cgi?id=1203).
To fix this, a PhantomReference is used to monitor when its corresponding JythonScriptEngine is garbage collected, at which point the PythonInterpreter is forcefully cleaned of local variables.
To avoid mutual hard references, the JythonScriptEngine and containing ScriptModule must never be passed to the PythonInterpreter. Instead, they can be cached in a Java-side map to weak references.