add static function to get lockIndex of some block

servers/src/main/java/tachyon/worker/block/BlockLockManager.java

@@ -45,6 +45,8 @@ public class BlockLockManager {
   private static final int NUM_LOCKS = 1000;
   /** The unique id of each lock */
   private static final AtomicLong LOCK_ID_GEN = new AtomicLong(0);
+  /** A hashing function to map blockId to one of the locks */
+  private static final HashFunction HASH_FUNC = Hashing.murmur3_32();
 
   /** The object that serves all metadata requests for the block store */
   private final BlockMetadataManager mMetaManager;
@@ -56,8 +58,6 @@ public class BlockLockManager {
   private final Map<Long, LockRecord> mLockIdToRecordMap = new HashMap<Long, LockRecord>();
   /** To guard access on mLockIdToRecordMap and mUserIdToLockIdsMap */
   private final Object mSharedMapsLock = new Object();
-  /** A hashing function to map blockId to one of the locks */
-  private final HashFunction mHashFunc = Hashing.murmur3_32();
 
   public BlockLockManager(BlockMetadataManager metaManager) {
     mMetaManager = Preconditions.checkNotNull(metaManager);
@@ -66,6 +66,10 @@ public BlockLockManager(BlockMetadataManager metaManager) {
     }
   }
 
+  public static int blockHashIndex(long blockId) {
+    return Math.abs(HASH_FUNC.hashLong(blockId).asInt()) % NUM_LOCKS;
+  }
+
   /**
    * Locks a block if it exists, throws IOException otherwise.
    *
@@ -77,8 +81,8 @@ public BlockLockManager(BlockMetadataManager metaManager) {
    */
   public long lockBlock(long userId, long blockId, BlockLockType blockLockType) throws IOException {
     // hashing blockId into the range of [0, NUM_LOCKS-1]
-    int hashValue = Math.abs(mHashFunc.hashLong(blockId).asInt()) % NUM_LOCKS;
-    ClientRWLock blockLock = mLockArray[hashValue];
+    int index = blockHashIndex(blockId);
+    ClientRWLock blockLock = mLockArray[index];
     Lock lock;
     if (blockLockType == BlockLockType.READ) {
       lock = blockLock.readLock();