JDK-6404561 : (thread) ThreadLocal lock contention
  • Type: Bug
  • Component: core-libs
  • Sub-Component: java.lang
  • Affected Version: 6
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • OS: generic
  • CPU: generic
  • Submitted: 2006-03-27
  • Updated: 2010-08-19
  • Resolved: 2006-05-30
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JDK 6
6 b86Fixed
Related Reports
Relates :  
JDK-6254531 - (thread) Provide reclaimable thread local values without Thread termination
Description
The ThreadLocal implementation uses an inefficient lock approach to protecting hash code generation. This causes needless contention overhead. Replacing the lock usage with an atomic get-add provides a clear performance boost for cases where contention is significant.
Comments
SUGGESTED FIX % diff ~/1.6.0/j2se/martin/j2se/src/share/classes/java/lang/ThreadLocal.java . 66c66 < * The next hash code to be given out. Accessed only by like-named method.--- > * The next hash code to be given out. Updated atomically. 68c68,69 < private static int nextHashCode = 0; --- > private static java.util.concurrent.atomic.AtomicInteger nextHashCode = > new java.util.concurrent.atomic.AtomicInteger(); 78,82c79 < * Compute the next hash code. The static synchronization used here < * should not be a performance bottleneck. When ThreadLocals are < * generated in different threads at a fast enough rate to regularly < * contend on this lock, memory contention is by far a more serious < * problem than lock contention. --- > * Returns the next hash code. 84,87c81,82 < private static synchronized int nextHashCode() { < int h = nextHashCode; < nextHashCode = h + HASH_INCREMENT; < return h; --- > private static int nextHashCode() { > return nextHashCode.getAndAdd(HASH_INCREMENT); %
27-03-2006
EVALUATION This improvment was submitted for Mustang by a ThreadLocal author.
27-03-2006