| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more contributor license |
| * agreements. See the NOTICE file distributed with this work for additional information regarding |
| * copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance with the License. You may obtain a |
| * copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software distributed under the License |
| * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express |
| * or implied. See the License for the specific language governing permissions and limitations under |
| * the License. |
| */ |
| package org.apache.geode.internal.util.concurrent; |
| |
| import java.util.concurrent.Semaphore; |
| import java.util.concurrent.TimeUnit; |
| import java.util.concurrent.locks.Condition; |
| import java.util.concurrent.locks.Lock; |
| import java.util.concurrent.locks.ReadWriteLock; |
| |
| /** |
| * This ReadWriteLock is useful when different threads need to lock and unlock the read lock. This |
| * is <b>NOT</b> a reentrant lock. |
| * |
| */ |
| public class SemaphoreReadWriteLock implements ReadWriteLock { |
| |
| private SemaphoreReadLock readLock; |
| private SemaphoreWriteLock writeLock; |
| |
| public SemaphoreReadWriteLock() { |
| Semaphore writerSemaphore = new Semaphore(1); |
| Semaphore readerSemaphore = new Semaphore(1); |
| readLock = new SemaphoreReadLock(readerSemaphore, writerSemaphore); |
| writeLock = new SemaphoreWriteLock(writerSemaphore); |
| } |
| |
| @Override |
| public Lock readLock() { |
| return readLock; |
| } |
| |
| @Override |
| public Lock writeLock() { |
| return writeLock; |
| } |
| |
| public static class SemaphoreReadLock implements Lock { |
| private int numReaders = 0; |
| private final Semaphore readerSemaphore; |
| private final Semaphore writerSemaphore; |
| |
| public SemaphoreReadLock(Semaphore readerSemaphore, Semaphore writerSemaphore) { |
| this.readerSemaphore = readerSemaphore; |
| this.writerSemaphore = writerSemaphore; |
| } |
| |
| @Override |
| public void lock() { |
| boolean interrupted = false; |
| try { |
| for (;;) { |
| try { |
| lockInterruptibly(); |
| break; |
| } catch (InterruptedException e) { |
| interrupted = true; |
| } |
| } |
| } finally { |
| if (interrupted) |
| Thread.currentThread().interrupt(); |
| } |
| } |
| |
| @Override |
| public void lockInterruptibly() throws InterruptedException { |
| readerSemaphore.acquire(); |
| try { |
| numReaders++; |
| if (numReaders == 1) { |
| writerSemaphore.acquire(); |
| } |
| } finally { |
| // in case writeSemaphore.acquire throws Exception |
| readerSemaphore.release(); |
| } |
| } |
| |
| @Override |
| public boolean tryLock() { |
| boolean interrupted = false; |
| try { |
| for (;;) { |
| try { |
| return tryLock(0, TimeUnit.MILLISECONDS); |
| } catch (InterruptedException e) { |
| interrupted = true; |
| } |
| } |
| } finally { |
| if (interrupted) |
| Thread.currentThread().interrupt(); |
| } |
| } |
| |
| @Override |
| public boolean tryLock(long time, TimeUnit unit) throws InterruptedException { |
| if (readerSemaphore.tryAcquire(time, unit)) { |
| int oldNumReaders = numReaders; |
| numReaders++; |
| if (numReaders == 1) { |
| if (writerSemaphore.tryAcquire(time, unit)) { |
| readerSemaphore.release(); |
| return true; |
| } else { |
| numReaders = oldNumReaders; |
| readerSemaphore.release(); |
| return false; |
| } |
| } else { |
| readerSemaphore.release(); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| @Override |
| public void unlock() { |
| for (;;) { |
| boolean interrupted = false; |
| try { |
| readerSemaphore.acquire(); |
| } catch (InterruptedException e) { |
| interrupted = true; |
| continue; |
| } finally { |
| if (interrupted) |
| Thread.currentThread().interrupt(); |
| } |
| numReaders--; |
| // The unlock method is forgiving |
| if (numReaders <= 0) { |
| numReaders = 0; |
| if (writerSemaphore.availablePermits() == 0) { |
| writerSemaphore.release(); |
| } |
| } |
| readerSemaphore.release(); |
| break; |
| } |
| } |
| |
| @Override |
| public Condition newCondition() { |
| throw new UnsupportedOperationException(); |
| } |
| } |
| |
| public static class SemaphoreWriteLock implements Lock { |
| |
| private final Semaphore writerSemaphore; |
| |
| public SemaphoreWriteLock(Semaphore writerSemaphore) { |
| this.writerSemaphore = writerSemaphore; |
| } |
| |
| @Override |
| public void lock() { |
| boolean interrupted = false; |
| try { |
| for (;;) { |
| try { |
| lockInterruptibly(); |
| break; |
| } catch (InterruptedException e) { |
| interrupted = true; |
| } |
| } |
| } finally { |
| if (interrupted) |
| Thread.currentThread().interrupt(); |
| } |
| } |
| |
| @Override |
| public void lockInterruptibly() throws InterruptedException { |
| writerSemaphore.acquire(); |
| } |
| |
| @Override |
| public boolean tryLock() { |
| return writerSemaphore.tryAcquire(); |
| } |
| |
| @Override |
| public boolean tryLock(long time, TimeUnit unit) throws InterruptedException { |
| return writerSemaphore.tryAcquire(time, unit); |
| } |
| |
| @Override |
| public void unlock() { |
| writerSemaphore.release(); |
| } |
| |
| @Override |
| public Condition newCondition() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| } |
| } |