Performance Implication of doing frequent calls to totalMemory()/freeMemory() for java.lang.Runtime?

Question

I have to frequently check the memory usage by an application - it right does it every 60 seconds using java.lang.Runtime.freeMemory()/java.lang.Runtime.totalMemory()

What if I do the above say every 5 seconds - any performance implications?

(Hopefully not like System.gc() has)

The application runs on Linux/Solaris/Windows/HP-UX/AIX etc

Answer 1

Test it and see. If you can't construct a test that causes a meaningful drop in performance metrics than I guarantee you your users won't notice it either.

Gut feeling: shouldn't be a problem. Now whether an application that constantly monitors its memory has a good design...that's another question.

Answer 2

I tracked it down in openjdk jvm.cpp

JVM_ENTRY_NO_ENV(jlong, JVM_TotalMemory(void))
  JVMWrapper("JVM_TotalMemory");
  size_t n = Universe::heap()->capacity();
  return convert_size_t_to_jlong(n);
JVM_END

searching for the implementation of Universe lead to

public CollectedHeap heap() {
    try {
      return (CollectedHeap) heapConstructor.instantiateWrapperFor(collectedHeapField.getValue());
    } catch (WrongTypeException e) {
      return new CollectedHeap(collectedHeapField.getValue());
    }
  }

Oops CollectedHeap is an interface ... thus I came to the conclusion that mark-peters 'test and see' would be best.