RFR: JDK-8066859 java/lang/ref/OOMEInReferenceHandler.java failed with java.lang.Exception: Reference Handler thread died (original) (raw)
Peter Levart peter.levart at gmail.com
Thu May 7 10:25:21 UTC 2015
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On 05/07/2015 09:06 AM, Laurent Bourgès wrote:
Peter, I looked at Cleaner by curiosity and it seems to be not catching the oome from thunk.run ! If oome1 is thrown by thunk.run at line 150 then it is catched at line 157 but your new try/catch block (oome2) only encapsulates the doPriviledge block. If this block also throws a new oome2 due to the first oome1 (no memory left), it will work but I would have prefered a more explicit solution and check oome1 first ... My 2 cents (I am not a reviewer). Laurent
Laurent,
You have a point and I asked myself the same question. The question is how to treat OOME thrown from thunk.run(). Current behavior is to exit() JVM for any exception (Throwable). I maintained that semantics. I only added a handler for OOME thrown in the handler of the 1st exception. I might have just exit()-ed the VM if OOME is thrown, but leaving no trace and just exiting VM would not help anyone diagnose what went wrong. So I opted for keeping the VM running for a while by delaying the handling of 1st exception to "better times". If better times never come, then the application is probably stuck anyway.
An alternative would be to catch OOME from thunk.run() and ignore it (printing it out would be ugly if VM is left to run), but that would silently ignore OOMEs thrown from thunk.run() and noone would notice that Cleaner(s) might not have clean-ed up the resources they should.
The complete fix would be to inspect the code paths of all Cleaner.thunk's run() methods and see if and where they can throw exceptions (OOMEs in particular) and whether they can be prevented. I did that and found myself wandering deeply in the hotspot code that I don't understand completely. Cleaner's are used in the following places:
in java.lang.invoke.CallSite, to invalidate the dependent nmethods when the context class is GC-ed - that one was added recently. Intermittent failures of the test predate it's addition, so I would not suspect this one immediately.
in sun.misc.Perf, to detach the memory of a native ByteBuffer obtained from Perf.attach() when the ByteBuffer is GC-ed. The Java code-path does not have any allocations and the native code that does detaching is in hotspot/src/share/vm/prims/perf.cpp:
static JNINativeMethod perfmethods[] = { ... {CC"detach", CC"("BB")V", FN_PTR(Perf_Detach)},So c ...
PERF_ENTRY(void, Perf_Detach(JNIEnv *env, jobject unused, jobject buffer))
PerfWrapper("Perf_Detach");
if (!UsePerfData) { // With -XX:-UsePerfData, detach is just a NOP return; }
void* address = 0; jlong capacity = 0;
// get buffer address and capacity { ThreadToNativeFromVM ttnfv(thread); address = env->GetDirectBufferAddress(buffer); capacity = env->GetDirectBufferCapacity(buffer); }
PerfMemory::detach((char*)address, capacity, CHECK);
PERF_END
- in sun.nio.ch.IOVecWrapper, to deallocate native memory associated with the wrapper when it is GC-ed. The Java code-path does not perform any allocations and finally just calls native Unsafe.freeMemory(allocationAddress) where allocationAddress was obtained from Unsafe.allocateMemory(size). The native code for Unsafe.freeMemory is in hotspot/src/share/vm/prims/unsafe.cpp:
static JNINativeMethod methods[] = { ... {CC"freeMemory", CC"("ADR")V", FN_PTR(Unsafe_FreeMemory)}, ...
UNSAFE_ENTRY(void, Unsafe_FreeMemory(JNIEnv env, jobject unsafe, jlong addr)) UnsafeWrapper("Unsafe_FreeMemory"); void p = addr_from_java(addr); if (p == NULL) { return; } os::free(p); UNSAFE_END
- in sun.nio.fs.NativeBuffer, to deallocate native memory allocated for NativeBuffer by Unsafe.allocateMemory(size) with exactly the same Cleaner.thunk (Deallocator) as used in sun.nio.ch.IOVecWrapper.
Can anyone confirm whether the above two native methods can throw any exception or not?
Anyway. If none of the Cleaner.thunk's run() methods can throw any exception, then my handling of OOME is redundant and a code-path never taken. But I would still leave it there in case some new Cleaner use comes along which is not verified yet...
Regards, Peter
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