Re: ClassLoader deadlock

Sat, 06 Feb 2016 04:18:21 -0800

The security manager is non blocking, unfortunately java system classes aren't.
The policy provider in use thread confines PermissionCollection instances, which never leave the cpu cache, they are discarded immediately after use. 


The problem here is that two different threads are attempting to load 
the same class at the same time.



I'll have to make sure that all classes are loaded before the security 
manager becomes the system security manager, either that or eliminate 
the AccessControlContext check permission cache.



While the standard java security manager and policy provider consume 
around 10% cpu, this consumes less than 1%.


On 6/02/2016 9:57 PM, David Holmes wrote:

On 6/02/2016 9:39 PM, Peter Firmstone wrote:

Hmm, thought the new parallel lock stategy in ClassLoader wasn't
deadlock prone?  Guess I was wrong.



The deadlock is introduced by a custom security manager. SM's play a 
critical role in many parts of the core libraries so if they utilize 
synchronization then they can easily introduce deadlock.



Observation:  On an unrelated occassion, I had a URLClassLoader
synchronization hotspot (well not standard URLClassLoader, but a high
performance RFC3986 URL ClassLoader, that use normalized RFC3986 URI
instead of URL DNS lookup), I solved that problem by thread confining
class loading.  I've never experienced deadlock using thread
confinement, initially I was worried that there would be
interdependencies, however I didn't experience a problem, as the single
thread would always load the classes it needed.

I'm wondering if multiple locks for ClassLoader's might be the wrong
strategy, I found thread confinement was very performant.



Are you suggesting that a class-load request is actually transmitted 
to a single class-loading thread, while the initial thread blocks 
until the loading is complete? That would still seem prone to the same 
SM related deadlock scenario. And it would not generally be 
particularly performant.


I thought that too, until I tried it.

Would you like to see some performance figures?

Cheers,

Peter.



David


Regards,

Peter.

2016-02-06 21:06:07
Full thread dump Java HotSpot(TM) Client VM (25.0-b70 mixed mode):

"Service Thread" #9 daemon prio=9 os_prio=0 tid=0x14387400 nid=0xc54
runnable [0x00000000]
    java.lang.Thread.State: RUNNABLE

"C1 CompilerThread0" #8 daemon prio=9 os_prio=2 tid=0x14332c00
nid=0x111c waiting on condition [0x00000000]
    java.lang.Thread.State: RUNNABLE

"Attach Listener" #7 daemon prio=5 os_prio=2 tid=0x14331c00 nid=0x13d8
waiting on condition [0x00000000]
    java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #6 daemon prio=9 os_prio=2 tid=0x14331400 nid=0x10b8
runnable [0x00000000]
    java.lang.Thread.State: RUNNABLE

"Thread-1" #5 prio=10 os_prio=2 tid=0x14318800 nid=0x4a8 waiting for
monitor entry [0x03ded000]
    java.lang.Thread.State: BLOCKED (on object monitor)
         at

org.apache.river.concurrent.ReferenceCollection.iterator(ReferenceCollection.java:124) 



         at
org.apache.river.concurrent.ReferenceSet.hashCode(ReferenceSet.java:65)
         at

org.apache.river.concurrent.StrongReference.<init>(StrongReference.java:44) 


         at

org.apache.river.concurrent.StrongReference.<init>(StrongReference.java:57) 


         at

org.apache.river.concurrent.ReferenceFactory.create(ReferenceFactory.java:64) 



         at

org.apache.river.concurrent.ReferenceProcessor.referenced(ReferenceProcessor.java:128) 



         at

org.apache.river.concurrent.ReferenceProcessor.referenced(ReferenceProcessor.java:44) 



         at
org.apache.river.concurrent.ReferenceMap.wrapVal(ReferenceMap.java:244)
         at

org.apache.river.concurrent.ReferenceConcurrentMap.putIfAbsent(ReferenceConcurrentMap.java:68) 



         at

org.apache.river.api.security.CombinerSecurityManager.checkPermission(CombinerSecurityManager.java:261) 



         at

org.apache.river.api.security.CombinerSecurityManager.checkPermission(CombinerSecurityManager.java:202) 



         at
java.net.NetworkInterface.getHardwareAddress(NetworkInterface.java:447)
         at

java.util.concurrent.ThreadLocalRandom.initialSeed(ThreadLocalRandom.java:158) 



         at

java.util.concurrent.ThreadLocalRandom.<clinit>(ThreadLocalRandom.java:137) 


         at

java.util.concurrent.ConcurrentHashMap.fullAddCount(ConcurrentHashMap.java:2526) 



         at

java.util.concurrent.ConcurrentHashMap.addCount(ConcurrentHashMap.java:2266) 



         at

java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1070) 


         at

java.util.concurrent.ConcurrentHashMap.putIfAbsent(ConcurrentHashMap.java:1535) 




         at 
java.lang.ClassLoader.getClassLoadingLock(ClassLoader.java:463)

         at java.lang.ClassLoader.loadClass(ClassLoader.java:404)
         at java.lang.ClassLoader.loadClass(ClassLoader.java:411)
         - locked <0x03f624b8> (a java.lang.Object)

         at 
sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)

         at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
         at

org.cliffc.high_scale_lib.NonBlockingHashMap$SnapshotK.<init>(NonBlockingHashMap.java:1167) 



         at

org.cliffc.high_scale_lib.NonBlockingHashMap$2.iterator(NonBlockingHashMap.java:1200) 



         at

org.apache.river.concurrent.ReferenceProcessor$EnqueGarbageTask.run(ReferenceProcessor.java:166) 



         - locked <0x03ef8b30> (a
org.cliffc.high_scale_lib.NonBlockingHashMap)
         at
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
         at
java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
         at

java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.j 



ava:180)
         at

java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294 



)
         at

java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) 



         at

java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) 



         at java.lang.Thread.run(Thread.java:744)

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x14277800 nid=0x15cc in
Object.wait() [0x03cff000]
    java.lang.Thread.State: WAITING (on object monitor)
         at java.lang.Object.wait(Native Method)
         - waiting on <0x03e056d8> (a java.lang.ref.ReferenceQueue$Lock)
         at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:142)
         - locked <0x03e056d8> (a java.lang.ref.ReferenceQueue$Lock)
         at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:158)

         at 
java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)


"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x14271c00
nid=0x1398 in Object.wait() [0x144cf000]
    java.lang.Thread.State: WAITING (on object monitor)
         at java.lang.Object.wait(Native Method)
         - waiting on <0x03e05200> (a java.lang.ref.Reference$Lock)
         at java.lang.Object.wait(Object.java:502)
         at
java.lang.ref.Reference$ReferenceHandler.run(Reference.java:157)
         - locked <0x03e05200> (a java.lang.ref.Reference$Lock)

"main" #1 prio=5 os_prio=0 tid=0x017cf400 nid=0x1284 waiting for monitor
entry [0x0185e000]
    java.lang.Thread.State: BLOCKED (on object monitor)
         at java.lang.ClassLoader.loadClass(ClassLoader.java:406)
         - waiting to lock <0x03f624b8> (a java.lang.Object)

         at 
sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)

         at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
         at

org.apache.river.concurrent.ReferenceCollection.iterator(ReferenceCollection.java:124) 



         at
org.apache.river.concurrent.ReferenceSet.hashCode(ReferenceSet.java:65)
         at

org.apache.river.concurrent.StrongReference.<init>(StrongReference.java:44) 


         at

org.apache.river.concurrent.StrongReference.<init>(StrongReference.java:57) 


         at

org.apache.river.concurrent.ReferenceFactory.create(ReferenceFactory.java:64) 



         at

org.apache.river.concurrent.ReferenceProcessor.referenced(ReferenceProcessor.java:128) 



         at

org.apache.river.concurrent.ReferenceProcessor.referenced(ReferenceProcessor.java:44) 



         at
org.apache.river.concurrent.ReferenceMap.wrapVal(ReferenceMap.java:244)
         at

org.apache.river.concurrent.ReferenceConcurrentMap.putIfAbsent(ReferenceConcurrentMap.java:68) 



         at

org.apache.river.api.security.CombinerSecurityManager.checkPermission(CombinerSecurityManager.java:261) 



         at

org.apache.river.api.security.CombinerSecurityManager.checkPermission(CombinerSecurityManager.java:202) 



         at java.lang.System.checkIO(System.java:253)
         at java.lang.System.setErr(System.java:199)

         at 
org.apache.river.qa.harness.MasterTest.main(MasterTest.java:84)


"VM Thread" os_prio=2 tid=0x1426e400 nid=0x16a8 runnable

"VM Periodic Task Thread" os_prio=2 tid=0x14388400 nid=0x17a8 waiting on
condition

JNI global references: 19


Found one Java-level deadlock:
=============================
"Thread-1":
   waiting to lock monitor 0x142766ac (object 0x040ebee8, a [I),
   which is held by "main"
"main":
   waiting to lock monitor 0x14274a3c (object 0x03f624b8, a
java.lang.Object),
   which is held by "Thread-1"

Java stack information for the threads listed above:
===================================================
"Thread-1":
         at

org.apache.river.concurrent.ReferenceCollection.iterator(ReferenceCollection.java:124) 



         at
org.apache.river.concurrent.ReferenceSet.hashCode(ReferenceSet.java:65)
         at

org.apache.river.concurrent.StrongReference.<init>(StrongReference.java:44) 


         at

org.apache.river.concurrent.StrongReference.<init>(StrongReference.java:57) 


         at

org.apache.river.concurrent.ReferenceFactory.create(ReferenceFactory.java:64) 



         at

org.apache.river.concurrent.ReferenceProcessor.referenced(ReferenceProcessor.java:128) 



         at

org.apache.river.concurrent.ReferenceProcessor.referenced(ReferenceProcessor.java:44) 



         at
org.apache.river.concurrent.ReferenceMap.wrapVal(ReferenceMap.java:244)
         at

org.apache.river.concurrent.ReferenceConcurrentMap.putIfAbsent(ReferenceConcurrentMap.java:68) 



         at

org.apache.river.api.security.CombinerSecurityManager.checkPermission(CombinerSecurityManager.java:261) 



         at

org.apache.river.api.security.CombinerSecurityManager.checkPermission(CombinerSecurityManager.java:202) 



         at
java.net.NetworkInterface.getHardwareAddress(NetworkInterface.java:447)
         at

java.util.concurrent.ThreadLocalRandom.initialSeed(ThreadLocalRandom.java:158) 



         at

java.util.concurrent.ThreadLocalRandom.<clinit>(ThreadLocalRandom.java:137) 


         at

java.util.concurrent.ConcurrentHashMap.fullAddCount(ConcurrentHashMap.java:2526) 



         at

java.util.concurrent.ConcurrentHashMap.addCount(ConcurrentHashMap.java:2266) 



         at

java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1070) 


         at

java.util.concurrent.ConcurrentHashMap.putIfAbsent(ConcurrentHashMap.java:1535) 




         at 
java.lang.ClassLoader.getClassLoadingLock(ClassLoader.java:463)

         at java.lang.ClassLoader.loadClass(ClassLoader.java:404)
         at java.lang.ClassLoader.loadClass(ClassLoader.java:411)
         - locked <0x03f624b8> (a java.lang.Object)

         at 
sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)

         at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
         at

org.cliffc.high_scale_lib.NonBlockingHashMap$SnapshotK.<init>(NonBlockingHashMap.java:1167) 



         at

org.cliffc.high_scale_lib.NonBlockingHashMap$2.iterator(NonBlockingHashMap.java:1200) 



         at

org.apache.river.concurrent.ReferenceProcessor$EnqueGarbageTask.run(ReferenceProcessor.java:166) 



         - locked <0x03ef8b30> (a
org.cliffc.high_scale_lib.NonBlockingHashMap)
         at
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
         at
java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
         at

java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.j 



ava:180)
         at

java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294 



)
         at

java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) 



         at

java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) 



         at java.lang.Thread.run(Thread.java:744)
"main":
         at java.lang.ClassLoader.loadClass(ClassLoader.java:406)
         - waiting to lock <0x03f624b8> (a java.lang.Object)

         at 
sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)

         at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
         at

org.apache.river.concurrent.ReferenceCollection.iterator(ReferenceCollection.java:124) 



         at
org.apache.river.concurrent.ReferenceSet.hashCode(ReferenceSet.java:65)
         at

org.apache.river.concurrent.StrongReference.<init>(StrongReference.java:44) 


         at

org.apache.river.concurrent.StrongReference.<init>(StrongReference.java:57) 


         at

org.apache.river.concurrent.ReferenceFactory.create(ReferenceFactory.java:64) 



         at

org.apache.river.concurrent.ReferenceProcessor.referenced(ReferenceProcessor.java:128) 



         at

org.apache.river.concurrent.ReferenceProcessor.referenced(ReferenceProcessor.java:44) 



         at
org.apache.river.concurrent.ReferenceMap.wrapVal(ReferenceMap.java:244)
         at

org.apache.river.concurrent.ReferenceConcurrentMap.putIfAbsent(ReferenceConcurrentMap.java:68) 



         at

org.apache.river.api.security.CombinerSecurityManager.checkPermission(CombinerSecurityManager.java:261) 



         at

org.apache.river.api.security.CombinerSecurityManager.checkPermission(CombinerSecurityManager.java:202) 



         at java.lang.System.checkIO(System.java:253)
         at java.lang.System.setErr(System.java:199)

         at 
org.apache.river.qa.harness.MasterTest.main(MasterTest.java:84)


Found 1 deadlock.
























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