private long getMemoryAddress(Region region, String key) {
    Object entry = ((LocalRegion) region).getRegionEntry(key).getValue();
    assertTrue(entry instanceof OffHeapStoredObject);
    long memoryAddress = ((OffHeapStoredObject) entry).getAddress();
    assertTrue(memoryAddress > 0);
    return memoryAddress;
  }
Returns -1 if m1 is missing a key in m2, 1 if m2 is missing a key in m1, or 0 is they contain
the exact same keys.

@throws NullPointerException if either c1 or c2 is null
geode-core/src/integrationTest/java/org/apache/geode/internal/offheap/OffHeapValidationJUnitTest.java