Java heap dump & shut down - what order?

Question

I would like to detect an OutOfMemoryError, take a heap dump, and automatically exit the Java program. Say I have the following command-line arguments for my JVM:

-XX:OnOutOfMemoryError="kill -9 %p"
-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/usr/tmp

Which happens first? Does the process dump memory and then quit, or the other way around?

Answer 1

If you are using OpenJDK you can be sure when you are going to run the command set by -XX:OnOutOfMemoryError option.

Code taken from the OpenJDK source code. See: debug.cpp

void report_java_out_of_memory(const char* message) {
  static jint out_of_memory_reported = 0;

  // A number of threads may attempt to report OutOfMemoryError at around the
  // same time. To avoid dumping the heap or executing the data collection
  // commands multiple times we just do it once when the first threads reports
  // the error.
  if (Atomic::cmpxchg(1, &out_of_memory_reported, 0) == 0) {
    // create heap dump before OnOutOfMemoryError commands are executed
    if (HeapDumpOnOutOfMemoryError) {    
      tty->print_cr("java.lang.OutOfMemoryError: %s", message);
      HeapDumper::dump_heap_from_oome();
    }

    if (OnOutOfMemoryError && OnOutOfMemoryError[0]) {
      VMError err(message);
      err.report_java_out_of_memory();
    }
  }
} 

Just in case a short explanation:

1. First of all check if the HeapDumpOnOutOfMemoryError option was set. In that case run dump_heap_from_oome()
2. Sencondly if the OnOutOfMemoryError option was set, run report_java_out_of_memory()

So, for sure if you are using OpenJDK your process will dump memory and then quit.

Answer 2

I would rather rely on calling into a script that handles the ordering more deterministically i.e.

-XX:OnOutOfMemoryError="/<SomeStandardLocation>/heapAndQuit.sh"

heapAndQuit.sh will then employ a method to find the pid of the current process. One simple way to identify the pid is to use the log file location your process is writing to

lsof | grep /var/tmp/<yourlogfileName> | cut -d " " -f1 | uniq

I will then use jmap to dump and kill -9 subsequently