Hi David , the values are already user-inspectable via jcmd vm.info ,
however this way is not very user friendly (and I am not sure how stable it is
between updates / releases).
Probably not as stable as an API .
Best regards, Matthias
> -----Original Message-----
> From: David Holmes <david.hol...@oracle.com>
> Sent: Donnerstag, 20. September 2018 03:13
> To: Baesken, Matthias <matthias.baes...@sap.com>; 'hotspot-
> d...@openjdk.java.net' <hotspot-...@openjdk.java.net>; serviceability-
> d...@openjdk.java.net serviceability-dev@openjdk.java.net <serviceability-
> d...@openjdk.java.net>
> Subject: Re: OOM counters
>
> Hi Matthias,
>
>
> Those counters, as I recall, were added to the hs_err report purely to
> show if an application/test had been "playing too close to the edge"
> before it crashed. They were never intended as user-inspectable values.
>
> I have no opinion as to whether they should be.
>
> David
>
> On 19/09/2018 7:12 PM, Baesken, Matthias wrote:
> > Hello, Currently we have already counters in the Hotspot codebase
> > counting Java heap,
> >
> > Metaspace and class metaspace related OOMs.
> >
> > See declarations:
> >
> > jdk/src/hotspot/share/utilities/exceptions.hpp
> >
> > 107 // Count out of memory errors that are interesting in error diagnosis
> >
> > 108 static volatile int _out_of_memory_error_java_heap_errors;
> >
> > 109 static volatile int _out_of_memory_error_metaspace_errors;
> >
> > 110 static volatile int _out_of_memory_error_class_metaspace_errors;
> >
> > output :
> >
> > jdk/src/hotspot/share/utilities/exceptions.cpp
> >
> > 460void Exceptions::print_exception_counts_on_error(outputStream* st)
> {
> >
> > 461 print_oom_count(st, "java_heap_errors",
> > _out_of_memory_error_java_heap_errors);
> >
> > 462 print_oom_count(st, "metaspace_errors",
> > _out_of_memory_error_metaspace_errors);
> >
> > 463 print_oom_count(st, "class_metaspace_errors",
> > _out_of_memory_error_class_metaspace_errors);
> >
> > 464 if (_stack_overflow_errors > 0) {
> >
> > 465 st->print_cr("StackOverflowErrors=%d", _stack_overflow_errors);
> >
> > 466 }
> >
> > 467 if (_linkage_errors > 0) {
> >
> > 468 st->print_cr("LinkageErrors=%d", _linkage_errors);
> >
> > 469 }
> >
> > 470}
> >
> > But currently the output is only done from vmError.cpp , in case of
> >
> > a) error reporting
> >
> > b) jcmd vm.info (in case exceptions happened, otherwise the section
> > is not printed)
> >
> > (see void VMError::print_vm_info(outputStream* st) { ... } )
> >
> > It would be interesting for us to get the values of the existing
> > counters via JDK coding.
> >
> > In our proprietary JVM we had a similar mechanism.
> >
> > Is there anything planned for this (or even already something present) ?
> >
> > There exists already a class java/lang/management/MemoryMXBean.java
> > with a management interface for the memory system of
> >
> > the Java virtual machine. It contains some "getter" - methods like
> >
> > public int getObjectPendingFinalizationCount();
> >
> > public MemoryUsage getHeapMemoryUsage();
> >
> > Do you think we could add a method (or methods) for accessing the
> > existing OOM counters
> >
> > ( for example, public OomCounters getOutOfMemoryCounters(); ) ?
> >
> > Best regards, Matthias
> >
