| package org.apache.lucene.store; |
| |
| /* |
| * 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. |
| */ |
| |
| import org.apache.lucene.util.ThreadInterruptedException; |
| import java.io.IOException; |
| |
| /** An interprocess mutex lock. |
| * <p>Typical use might look like:<pre class="prettyprint"> |
| * new Lock.With(directory.makeLock("my.lock")) { |
| * public Object doBody() { |
| * <i>... code to execute while locked ...</i> |
| * } |
| * }.run(); |
| * </pre> |
| * |
| * @see Directory#makeLock(String) |
| */ |
| public abstract class Lock { |
| |
| /** How long {@link #obtain(long)} waits, in milliseconds, |
| * in between attempts to acquire the lock. */ |
| public static long LOCK_POLL_INTERVAL = 1000; |
| |
| /** Pass this value to {@link #obtain(long)} to try |
| * forever to obtain the lock. */ |
| public static final long LOCK_OBTAIN_WAIT_FOREVER = -1; |
| |
| /** Attempts to obtain exclusive access and immediately return |
| * upon success or failure. |
| * @return true iff exclusive access is obtained |
| */ |
| public abstract boolean obtain() throws IOException; |
| |
| /** |
| * If a lock obtain called, this failureReason may be set |
| * with the "root cause" Exception as to why the lock was |
| * not obtained. |
| */ |
| protected Throwable failureReason; |
| |
| /** Attempts to obtain an exclusive lock within amount of |
| * time given. Polls once per {@link #LOCK_POLL_INTERVAL} |
| * (currently 1000) milliseconds until lockWaitTimeout is |
| * passed. |
| * @param lockWaitTimeout length of time to wait in |
| * milliseconds or {@link |
| * #LOCK_OBTAIN_WAIT_FOREVER} to retry forever |
| * @return true if lock was obtained |
| * @throws LockObtainFailedException if lock wait times out |
| * @throws IllegalArgumentException if lockWaitTimeout is |
| * out of bounds |
| * @throws IOException if obtain() throws IOException |
| */ |
| public boolean obtain(long lockWaitTimeout) throws IOException { |
| failureReason = null; |
| boolean locked = obtain(); |
| if (lockWaitTimeout < 0 && lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER) |
| throw new IllegalArgumentException("lockWaitTimeout should be LOCK_OBTAIN_WAIT_FOREVER or a non-negative number (got " + lockWaitTimeout + ")"); |
| |
| long maxSleepCount = lockWaitTimeout / LOCK_POLL_INTERVAL; |
| long sleepCount = 0; |
| while (!locked) { |
| if (lockWaitTimeout != LOCK_OBTAIN_WAIT_FOREVER && sleepCount++ >= maxSleepCount) { |
| String reason = "Lock obtain timed out: " + this.toString(); |
| if (failureReason != null) { |
| reason += ": " + failureReason; |
| } |
| LockObtainFailedException e = new LockObtainFailedException(reason); |
| if (failureReason != null) { |
| e.initCause(failureReason); |
| } |
| throw e; |
| } |
| try { |
| Thread.sleep(LOCK_POLL_INTERVAL); |
| } catch (InterruptedException ie) { |
| throw new ThreadInterruptedException(ie); |
| } |
| locked = obtain(); |
| } |
| return locked; |
| } |
| |
| /** Releases exclusive access. */ |
| public abstract void release() throws IOException; |
| |
| /** Returns true if the resource is currently locked. Note that one must |
| * still call {@link #obtain()} before using the resource. */ |
| public abstract boolean isLocked() throws IOException; |
| |
| |
| /** Utility class for executing code with exclusive access. */ |
| public abstract static class With { |
| private Lock lock; |
| private long lockWaitTimeout; |
| |
| |
| /** Constructs an executor that will grab the named lock. */ |
| public With(Lock lock, long lockWaitTimeout) { |
| this.lock = lock; |
| this.lockWaitTimeout = lockWaitTimeout; |
| } |
| |
| /** Code to execute with exclusive access. */ |
| protected abstract Object doBody() throws IOException; |
| |
| /** Calls {@link #doBody} while <i>lock</i> is obtained. Blocks if lock |
| * cannot be obtained immediately. Retries to obtain lock once per second |
| * until it is obtained, or until it has tried ten times. Lock is released when |
| * {@link #doBody} exits. |
| * @throws LockObtainFailedException if lock could not |
| * be obtained |
| * @throws IOException if {@link Lock#obtain} throws IOException |
| */ |
| public Object run() throws IOException { |
| boolean locked = false; |
| try { |
| locked = lock.obtain(lockWaitTimeout); |
| return doBody(); |
| } finally { |
| if (locked) |
| lock.release(); |
| } |
| } |
| } |
| |
| } |