Handling collections in coherence cache

Question

hi,
In a mutithreaded environment, how does coherence cache handles collection like HashMap in a multithreaded environment where the large majority of method calls are read-only, instead of structural changes?
Are the read calls non-synchronized by coherence? Is there any mechanism to handle the write calls different from the read calls?
Thanks.
suvasis

Answer 1

Hi Suvasis,
Coherence caches are coherent, and use a minimal (or zero if possible) amount of synchronization for read-access.
Coherence does support double-checked locking for read-heavy access:
<tt>
Object value = cache.get(k);
if (value == null)
  cache.lock(key, -1);
  try
    value = cache.get(key);
    if (value == null)
      value = {something};
      cache.put(key, value);
  finally
    cache.unlock(key);
// read-access to value
Object x = value.getSomeAttribute();
</tt>
It should be noted that Coherence does not "observe" objects outside of the Coherence API calls (get/put/lock/unlock/etc). So once you "get" a local object instance from Coherence, Coherence doesn't pay attention to that local object until you explicitly "put" it the modified object back into the cache.
Jon Purdy
Tangosol, Inc.