/*
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
licenses@blazegraph.com
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Jun 26, 2009
*/
package com.bigdata.util.concurrent;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.log4j.Logger;
import com.bigdata.util.InnerCause;
/**
* A synchronization aid that allows one or more threads to await a counter
* becoming zero. Once the counter reaches zero, all waiting threads are
* released. Threads may invoke {@link #await()} any time after the counter has
* been incremented. They will not be released until the counter is zero. The
* typical pattern is to incrementing the counter before some operation and the
* decrement the counter after that operation. This pattern may be safely used
* in combination with nested invocations and with concurrent threads.
* <p>
* Note: This class is very similar to a {@link CountDownLatch}, however the
* counter maximum is not specified in advance.
*
* @author <a href="mailto:thompsonbry@users.sourceforge.net">Bryan Thompson</a>
* @version $Id$
*/
public class Latch {
protected transient static final Logger log = Logger.getLogger(Latch.class);
private final AtomicLong counter = new AtomicLong();
private final ReentrantLock lock;
private final Condition cond;
private final String name;
public String toString() {
return getClass().getName() + "{"
+ (name == null ? "" : "name=" + name + ",") + "counter="
+ counter + "}";
}
public Latch() {
this(null/* name */, null/* lock */);
}
/**
*
* @param lock
* The lock to be used (optional). When none is specified, a new
* lock will be allocated. The caller MAY choose to specify the
* lock in order to avoid nested lock designs by using the same
* lock inside the {@link Latch} and in some outer context.
*/
public Latch(final ReentrantLock lock) {
this(null/* name */, lock);
}
/**
*
* @param name
* An optional name that will be displayed by {@link #toString()}
* along with the current counter value.
* @param lock
* The lock to be used (optional). When none is specified, a new
* lock will be allocated. The caller MAY choose to specify the
* lock in order to avoid nested lock designs by using the same
* lock inside the {@link Latch} and in some outer context.
*/
public Latch(final String name, final ReentrantLock lock) {
this.name = name; // MAY be null.
this.lock = (lock == null ? new ReentrantLock() : lock);
this.cond = this.lock.newCondition();
}
/**
* The counter value (peek at current value without obtaining the lock).
*/
public long get() {
return counter.get();
}
/**
* Increments the internal counter.
*
* @return The post-increment value of the counter.
*/
public long inc() {
lock.lock();
try {
final long c = this.counter.incrementAndGet();
if (c <= 0)
throw new IllegalStateException(toString());
if (log.isDebugEnabled())
log.debug(toString());
return c;
} finally {
lock.unlock();
}
}
/**
* Adds the delta to the internal counter.
*
* @return The post-increment value of the counter.
*/
public long addAndGet(final long delta) {
lock.lock();
try {
if (this.counter.get() + delta < 0) {
throw new IllegalStateException(toString());
}
final long c = this.counter.addAndGet(delta);
if (log.isDebugEnabled())
log.debug(toString());
if (c == 0) {
// try {
// signal blocked threads.
_signal();
// } catch (InterruptedException ex) {
//
// throw new RuntimeException(ex);
//
// }
}
return c;
} finally {
lock.unlock();
}
}
/**
* Decrements the internal counter and releases the blocked thread(s) if the
* counter reaches zero.
*
* @return The post-decrement value.
*
* @throws IllegalStateException
* if the counter would become negative.
*/
public long dec() {
lock.lock();
try {
if (this.counter.get() <= 0) {
throw new IllegalStateException(toString());
}
final long c = this.counter.decrementAndGet();
if (log.isDebugEnabled())
log.debug(toString());
if (c == 0) {
// try {
// signal blocked threads.
_signal();
// } catch (InterruptedException ex) {
//
// throw new RuntimeException(ex);
//
// }
}
return c;
} finally {
lock.unlock();
}
}
/**
* Signal any threads blocked in {@link #await(long, TimeUnit)}.
*/
/*
* Modified 28 May 2010 by BBT to not be interruptable. This is called from
* within inc() and dec() and we want those methods to complete normally so
* the counter does not get out of whack.
*/
// *
// * @throws InterruptedException
private final void _signal() { //throws InterruptedException {
if(!lock.isHeldByCurrentThread())
throw new IllegalMonitorStateException();
// lock.lock();
//// lock.lockInterruptibly();
// try {
if (log.isInfoEnabled())
log.info("signalAll()");
// release anyone awaiting our signal.
cond.signalAll();
// } finally {
//
// lock.unlock();
//
// }
try {
// allow extensions.
signal();
} catch (InterruptedException t) {
// propagate to the caller.
Thread.currentThread().interrupt();
// } catch (InterruptedException t) {
// // propagate to the caller.
// throw t;
} catch (Throwable t) {
// log anything else thrown out.
log.error(toString(), t);
if(InnerCause.isInnerCause(t, InterruptedException.class)) {
// propagate the interrupt.
Thread.currentThread().interrupt();
}
}
}
/**
* Invoked when the latch reaches zero after any threads blocked at
* {@link #await(long, TimeUnit)} have been released. This may be overridden
* to perform additional processing, such as moving an associated object
* onto another queue.
* <p>
* CAUTION: DO NOT invoke any operation from within this method which could
* block as that would cause the thread running the asynchronous write task
* in which this method is invoked to block. If you are transferring objects
* to a queue, the queue MUST be unbounded.
*/
protected void signal() throws InterruptedException {
}
/**
* Await the counter to become zero unless interrupted.
*
* @throws InterruptedException
*/
public void await() throws InterruptedException {
await(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
}
/**
* Await the counter to become zero, but no longer than the timeout.
*
* @param timeout
* The timeout.
* @param unit
* The unit in which the timeout is expressed.
*
* @return <code>true</code> if the counter reached zero and
* <code>false</code> if the timeout was exceeded before the counter
* reached zero.
*
* @throws InterruptedException
*/
public boolean await(final long timeout, final TimeUnit unit)
throws InterruptedException {
final long start = System.nanoTime();
final long nanos = unit.toNanos(timeout);
long remaining = nanos;
if (lock.tryLock(remaining, TimeUnit.NANOSECONDS)) {
try {
// subtract out the lock waiting time.
remaining = nanos - (System.nanoTime() - start);
long c;
while ((c = counter.get()) != 0) {
if (c < 0)
throw new IllegalStateException(toString());
if (remaining > 0)
remaining = cond.awaitNanos(remaining);
else
return false;
}
return true;
} finally {
lock.unlock();
}
}
// Timeout.
return false;
}
}