001package org.eclipse.aether.named.support; 002 003/* 004 * Licensed to the Apache Software Foundation (ASF) under one 005 * or more contributor license agreements. See the NOTICE file 006 * distributed with this work for additional information 007 * regarding copyright ownership. The ASF licenses this file 008 * to you under the Apache License, Version 2.0 (the 009 * "License"); you may not use this file except in compliance 010 * with the License. You may obtain a copy of the License at 011 * 012 * http://www.apache.org/licenses/LICENSE-2.0 013 * 014 * Unless required by applicable law or agreed to in writing, 015 * software distributed under the License is distributed on an 016 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 017 * KIND, either express or implied. See the License for the 018 * specific language governing permissions and limitations 019 * under the License. 020 */ 021 022import java.util.ArrayDeque; 023import java.util.Deque; 024import java.util.concurrent.TimeUnit; 025import java.util.concurrent.locks.ReadWriteLock; 026 027/** 028 * Named lock support implementation that is using {@link ReadWriteLock} instances. The adapted lock MUST SUPPORT 029 * reentrancy, non re-entrant locks will NOT work. It is the responsibility of an adapting lock, to ensure that 030 * above lock requirement stands. 031 */ 032public class ReadWriteLockNamedLock 033 extends NamedLockSupport 034{ 035 private enum Step 036 { 037 /** 038 * Step when {@link ReadWriteLock#readLock()} was locked 039 */ 040 SHARED, 041 042 /** 043 * Step when {@link ReadWriteLock#writeLock()} was locked 044 */ 045 EXCLUSIVE 046 } 047 048 private final ThreadLocal<Deque<Step>> threadSteps; 049 050 private final ReadWriteLock readWriteLock; 051 052 public ReadWriteLockNamedLock( final String name, 053 final NamedLockFactorySupport factory, 054 final ReadWriteLock readWriteLock ) 055 { 056 super( name, factory ); 057 this.threadSteps = ThreadLocal.withInitial( ArrayDeque::new ); 058 this.readWriteLock = readWriteLock; 059 } 060 061 @Override 062 public boolean lockShared( final long time, final TimeUnit unit ) throws InterruptedException 063 { 064 Deque<Step> steps = threadSteps.get(); 065 if ( readWriteLock.readLock().tryLock( time, unit ) ) 066 { 067 steps.push( Step.SHARED ); 068 return true; 069 } 070 return false; 071 } 072 073 @Override 074 public boolean lockExclusively( final long time, final TimeUnit unit ) throws InterruptedException 075 { 076 Deque<Step> steps = threadSteps.get(); 077 if ( !steps.isEmpty() ) 078 { // we already own shared or exclusive lock 079 if ( !steps.contains( Step.EXCLUSIVE ) ) 080 { 081 return false; // Lock upgrade not supported 082 } 083 } 084 if ( readWriteLock.writeLock().tryLock( time, unit ) ) 085 { 086 steps.push( Step.EXCLUSIVE ); 087 return true; 088 } 089 return false; 090 } 091 092 @Override 093 public void unlock() 094 { 095 Deque<Step> steps = threadSteps.get(); 096 if ( steps.isEmpty() ) 097 { 098 throw new IllegalStateException( "Wrong API usage: unlock without lock" ); 099 } 100 Step step = steps.pop(); 101 if ( Step.SHARED == step ) 102 { 103 readWriteLock.readLock().unlock(); 104 } 105 else if ( Step.EXCLUSIVE == step ) 106 { 107 readWriteLock.writeLock().unlock(); 108 } 109 } 110}