001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.hadoop.hdfs.util;
019    
020    /** Read-write lock interface. */
021    public interface RwLock {
022      /** Acquire read lock. */
023      public void readLock();
024      
025      /**
026       * Acquire the long read lock, unless interrupted while waiting. The long
027       * read lock should also serve to block all concurrent writers.
028       **/
029      void longReadLockInterruptibly() throws InterruptedException;
030      
031      /** Release the long read lock. */
032      public void longReadUnlock();
033    
034      /** Release read lock. */
035      public void readUnlock();
036    
037      /** Check if the current thread holds read lock. */
038      public boolean hasReadLock();
039    
040      /** Acquire write lock. */
041      public void writeLock();
042      
043      /** Acquire write lock, unless interrupted while waiting  */
044      void writeLockInterruptibly() throws InterruptedException;
045    
046      /** Release write lock. */
047      public void writeUnlock();
048    
049      /** Check if the current thread holds write lock. */
050      public boolean hasWriteLock();
051    }