[infinispan-dev] race condition in AsyncStore

[Mircea Markus]

Hi Galder,

This is following an email sent this morning on an infinit loop in  
AsyncTest. I've found what was[1] causing the infinite loop. Here it  
is (see comments in the code):

Let's say we do put(k1, v1) and put(k1, v2) in this order


       void run0() throws InterruptedException {
          if (trace) log.trace("Checking for modifications");
          boolean unlock = false;
          try {
             acquireLock(write);
             unlock = true;
             swap = state;
             state = newStateMap();
          } finally {
             if (unlock) write.unlock();
          }
//thread ONE comes here and is processing (k1, v1); it releases the  
write lock. Immediately, thread TWO acquires write lock, and takes  
(k1,v2) from the store into its swap.
// the race condition happens when thread TWO executes (i.e. persists)  
before thread one, and as a result in the store the final value  
persisted is v1 (not v2).
// This is known to be an async (i.e. best effort store), so this  
situation might be considered as normal behavior. Still, I think this  
induces unwanted errors/behavior.
// A possible solution is to only release the WL after put(swap).


          if (trace) log.trace("About to insert the swap: " + swap);
          int size = swap.size();
          if (size == 0)
             awaitNotEmpty();
          else
             decrementAndGet(size);

          if (trace) log.trace("Calling put(List) with {0}  
modifications", size);
          put(swap);
       }

Cheers,
Mircea



[1] I say 'was' because I modified the test to fail (intermittently)  
rather than hang