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  1. JDK
  2. JDK-8028280

ParkEvent leak when running modified runThese which only loads classes



    • Type: Bug
    • Status: Closed
    • Priority: P2
    • Resolution: Fixed
    • Affects Version/s: hs25
    • Fix Version/s: 9
    • Component/s: hotspot
    • Environment:
    • Subcomponent:
    • Resolved In Build:
    • CPU:
    • OS:
    • Verification:
      Not verified



        When running runTheseC (compileThese) we've run into native OOME, primarily on 32 bit windows builds running on large windows machines.

        I left runTheseC running overnight on a Solaris machine in the hope of using libumem's memory leak detection but I couldn't get any useful information from it, but we're definitely leaking something:
        $ pmap 5287 |grep heap
        0000000000411000 4193312K rw--- [ heap ]
        0000000100319000 2350824K rw--- [ heap ]
        Metaspace usage is around 11MB with 40MB committed so we don't have a lot of live classes it seems.

        Using libumem to gather some snapshots of all malloc() calls in a run. One thing that shows up is allocation of ParkEvents which are leaked (intentionally, it appears).
        runThese aggresively spawns threads which open JAR files, which seem to end up in JVM_RawMonitorEnter:

        ParkEvents on Solaris are 440 bytes each, and there are >10000 of them on the ParkEvent::FreeList after an hour of running the compileThese version of runThese.

        I also tried an instrumented build on Windows, where I use HeapCreate to create a separate memory heap for allocating ParkEvents to be able to track them externally to the process. After running runTheseC for around 30 minutes that heap has grown to 256MB.

        A theory for the root cause of this is that ParkEvent::Allocate is not designed to handle the load of 15-16 threads contending on a Monitor* through the JVM_RawMonitor* API.
        Using the RawMonitor functions disallows the VM from using the JavaThread's ParkEvent and forces all those contending threads to hit ParkEvent::Allocate.

        ParkEvents are maintained on a lock-free free list which is designed to avoid ABA problems by doing push-one pop-all, so there is a potential for allocation spikes while one thread is CAS:ing on the FreeList.

        I=H (aggressive memory leak if this problem occurs, can easily lead to crash due to OOME)
        L=L (very unlikely situation)
        W=H (no known work-around if this situation arises)


          1. detail.diff.log
            48 kB
          2. ParkEventLeak.c
            27 kB
          3. parkevent-win32.diff
            3 kB
          4. sa-parkevent.diff
            6 kB

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                dsimms David Simms
                mgerdin Mikael Gerdin (Inactive)
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