HBASE-4289 Move spinlock to SingleSizeCache rather than the slab allocator

(Li Pi)


git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1163215 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -435,6 +435,8 @@ Release 0.91.0 - Unreleased
                modifying TableMapReduceUtil.initTableMapperJob() (Brock Noland)
    HBASE-4185  Add doc for new hfilev2 format
    HBASE-4315  RS requestsPerSecond counter seems to be off (subramanian raghunathan)
+   HBASE-4289  Move spinlock to SingleSizeCache rather than the slab allocator
+               (Li Pi)
 
   NEW FEATURES
    HBASE-2001  Coprocessors: Colocate user code with regions (Mingjie Lai via

src/main/java/org/apache/hadoop/hbase/io/hfile/slab/SingleSizeCache.java

@@ -118,8 +118,16 @@ public class SingleSizeCache implements BlockCache {
 
   @Override
   public synchronized void cacheBlock(String blockName, Cacheable toBeCached) {
-    ByteBuffer storedBlock = backingStore.alloc(toBeCached
-        .getSerializedLength());
+    ByteBuffer storedBlock;
+
+    /*
+     * Spinlock if empty, Guava Mapmaker guarantees that we will not store more
+     * items than the memory we have allocated, but the Slab Allocator may still
+     * be empty if we have not yet completed eviction
+     */
+    do {
+      storedBlock = backingStore.alloc(toBeCached.getSerializedLength());
+    } while (storedBlock == null);
 
     CacheablePair newEntry = new CacheablePair(toBeCached.getDeserializer(),
         storedBlock);

src/main/java/org/apache/hadoop/hbase/io/hfile/slab/Slab.java

@@ -108,16 +108,17 @@ class Slab implements org.apache.hadoop.hbase.io.HeapSize {
   }
 
   /*
-   * This spinlocks if empty. Make sure your program can deal with that, and
-   * will complete eviction on time.
+   * This returns null if empty. Throws an exception if you try to allocate a
+   * bigger size than the allocator can handle.
    */
   ByteBuffer alloc(int bufferSize) {
     int newCapacity = Preconditions.checkPositionIndex(bufferSize, blockSize);
 
     ByteBuffer returnedBuffer = buffers.poll();
-    while(returnedBuffer == null){
-      returnedBuffer = buffers.poll();
+    if (returnedBuffer == null) {
+      return null;
     }
+
     returnedBuffer.clear().limit(newCapacity);
     return returnedBuffer;
   }