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  1. JDK
  2. JDK-6317330

Use ReentrantLock to serialize access to Xlib, etc for improved performance

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    Details

    • Type: Bug
    • Status: Resolved
    • Priority: P3
    • Resolution: Fixed
    • Affects Version/s: 5.0
    • Fix Version/s: 6
    • Component/s: client-libs
    • Labels:
    • Subcomponent:
      2d
    • Resolved In Build:
      b53
    • CPU:
      generic
    • OS:
      solaris_9

      Description

      While investigating rendering performance for the X11 pipeline, we have determined
      that a significant bottleneck is our use of the "AWT lock" to serialize access to
      Xlib, Motif, and other native libraries. The problem is that the AWT lock is almost
      always promoted to a very expensive, heavyweight monitor because a) there is often
      contention for the lock and b) we acquire the lock by a combination of the JNI and
      Unsafe monitorEnter() entrypoints, both of which cause the lock to be "inflated". An
      "inflated" Java object monitor has been shown to be many times slower than a
      non-inflated monitor.

      This was first reported in 4740695, and a bug was filed
      (4922864) to use pthread mutex instead. However, this bug was quickly closed because
      XAWT code almost always acquires the lock from the Java side using either the
      synchronized keyword or the Unsafe entrypoints, so using pthread mutexes to lock
      would require frequent JNI downcalls, which would be even worse for performance.

      In JDK 5, the java.util.concurrent.locks.ReentrantLock class was introduced offering
      a lightweight locking solution that performs very well under contention, especially
      when compared to Java object monitors. We used ReentrantLock in the single-threaded
      OGL pipeline rearchitecture in Mustang with very positive results, which got us
      thinking that maybe ReentrantLock would be a good replacement for the AWT lock.

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              Assignee:
              campbell Christopher Campbell (Inactive)
              Reporter:
              campbell Christopher Campbell (Inactive)
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