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
