JDK-6990754 : Use native memory and reference counting to implement SymbolTable
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: runtime
  • Affected Version: hs20
  • Priority: P3
  • Status: Closed
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2010-10-08
  • Updated: 2013-06-12
  • Resolved: 2011-03-08
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JDK 7 Other
7Fixed hs21Fixed
Related Reports
Relates :  
JDK-7023180 - Change in specified-to-be-unspecified ordering of getDeclaredMethods causes application problems
Relates :  
JDK-6964458 - Reimplement class meta-data storage to use native memory
Relates :  
JDK-7018673 - Zero: 6953144, 6990754 and 7009756 made some changes which broke Zero
Relates :  
JDK-7018355 - JSR 292: VM crash in DefNewGeneration::copy_to_survivor_space
Relates :  
JDK-7171703 - JNI DefineClass crashes client VM when first parameter is NULL
Relates :  
JDK-8009204 - [dtrace] signatures returned by Java 7 jstack() are corrupt on Solaris
Description
As designed now, customers of Hotspot have to specify a fixed size for the permanent generation, which is a part of the Java heap that holds the VM's representation of the classfiles and other types in a java program.  This is called "metadata" within hotspot. If there are a lot of classes loaded, the JVM can throw OutOfMemoryError for the permanent generation when there is plenty of Java heap space and native C heap space available.  The customer would then need to restart the VM with a larger MaxPermSize parameter.

One of the solutions to this problem is to use native C memory for the VM's representation of the Java program.  This is currently our chosen solution.  The SymbolTable and associated symbols are one type in the JVM that needs to move into native memory, from permgen.  The symbols are shared among class loaders so need to be reference counted so that when unreferenced, they are freed.

This work supports bugid 6964458
Comments
EVALUATION Summary: move symbols from permgen into C heap and reference count them Reviewed-by: never, acorn, jmasa, stefank
02-02-2011
EVALUATION http://hg.openjdk.java.net/jdk7/hotspot-rt/hotspot/rev/3582bf76420e
30-01-2011
EVALUATION http://hg.openjdk.java.net/jdk7/hotspot-rt/hotspot/rev/3582bf76420e
30-01-2011