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>
* 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 LockObtainFailedException, 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 LockObtainFailedException, IOException {
boolean locked = false;
try {
locked = lock.obtain(lockWaitTimeout);
return doBody();
} finally {
if (locked)
lock.release();
}
}
}
}