SPY-163: Count down bulk get latch even when empty key list is provided.

Motivation
----------
When a empty iterator (or empty key list) is passed in to a get bulk operation,
a result is never returned and the thread is blocked because it waits on a
latch that will never be counted down (because no response will ever arrive).

Modifications
-------------
If no chunks with keys are sent out to the servers, the latch is initialized
to 0 right away so that the code doesn't need to wait at all.

Result
------
The code now returns properly with an empty map instead of blocking the thread
forever.

Change-Id: I0711c399d9f15010bc808e0f651ce6ad605c06f0
Reviewed-on: http://review.couchbase.org/36208
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>

Author: daschl

src/main/java/net/spy/memcached/MemcachedClient.java

@@ -1317,7 +1317,8 @@ public <T> BulkFuture<Map<String, T>> asyncGetBulk(Iterator<String> keyIter,
     }
 
     final AtomicInteger pendingChunks = new AtomicInteger(chunks.size());
-    final CountDownLatch latch = new CountDownLatch(1);
+    int initialLatchCount = chunks.isEmpty() ? 0 : 1;
+    final CountDownLatch latch = new CountDownLatch(initialLatchCount);
     final Collection<Operation> ops = new ArrayList<Operation>(chunks.size());
     final BulkGetFuture<T> rv = new BulkGetFuture<T>(m, ops, latch, executorService);
 

src/test/java/net/spy/memcached/ProtocolBaseCase.java

@@ -1006,6 +1006,11 @@ public void onComplete(BulkGetFuture<?> f) throws Exception {
     assertTrue(latch.await(2, TimeUnit.SECONDS));
   }
 
+  public void testEmptyGetBulk() throws Exception {
+    Map<String, Object> bulk = client.getBulk(Collections.<String>emptyList());
+    assertTrue(bulk.isEmpty());
+  }
+
   private static class TestTranscoder implements Transcoder<String> {
     private static final int FLAGS = 238885206;