io.debezium.util.VariableLatch Maven / Gradle / Ivy
/*
* Based on java.util.concurrent.CountDownLatch, which was
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*
* Any changes relative to CountDownLatch are also released to the
* public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package io.debezium.util;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import io.debezium.annotation.ThreadSafe;
/**
* A latch that works similarly to {@link CountDownLatch} except that it can also increase the count dynamically.
*/
@ThreadSafe
public class VariableLatch {
/**
* Create a new variable latch.
*
* @return the variable latch; never null
*/
public static VariableLatch create() {
return create(0);
}
/**
* Create a new variable latch.
*
* @param initialValue the initial number of latches
* @return the variable latch; never null
*/
public static VariableLatch create(int initialValue) {
return new VariableLatch(initialValue);
}
/**
* Synchronization control For CountDownLatch.
* Uses AQS state to represent count.
*/
private static final class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 4982264981922014374L;
Sync(int count) {
setState(count);
}
int getCount() {
return getState();
}
@Override
protected int tryAcquireShared(int acquires) {
return (getState() == 0) ? 1 : -1;
}
@Override
protected boolean tryReleaseShared(int releases) {
// Increment or decrement count; signal when transition to zero
for (;;) {
int c = getState();
if (c == 0 && releases >= 0) {
return false;
}
int nextc = c - releases;
if (nextc < 0) {
nextc = 0;
}
if (compareAndSetState(c, nextc)) {
return nextc == 0;
}
}
}
}
private final Sync sync;
/**
* Constructs a {@code CountDownLatch} initialized with the given count.
*
* @param count the number of times {@link #countDown} must be invoked
* before threads can pass through {@link #await}
* @throws IllegalArgumentException if {@code count} is negative
*/
public VariableLatch(int count) {
if (count < 0) {
throw new IllegalArgumentException("count < 0");
}
this.sync = new Sync(count);
}
/**
* Causes the current thread to wait until the latch has counted down to
* zero, unless the thread is {@linkplain Thread#interrupt interrupted}.
*
*
* If the current count is zero then this method returns immediately.
*
*
* If the current count is greater than zero then the current thread becomes disabled for thread scheduling purposes and lies
* dormant until one of two things happen:
*
* - The count reaches zero due to invocations of the {@link #countDown} method; or
*
- Some other thread {@linkplain Thread#interrupt interrupts} the current thread.
*
*
*
* If the current thread:
*
* - has its interrupted status set on entry to this method; or
*
- is {@linkplain Thread#interrupt interrupted} while waiting,
*
* then {@link InterruptedException} is thrown and the current thread's interrupted status is cleared.
*
* @throws InterruptedException if the current thread is interrupted
* while waiting
*/
public void await() throws InterruptedException {
sync.acquireSharedInterruptibly(1);
}
/**
* Causes the current thread to wait until the latch has counted down to
* zero, unless the thread is {@linkplain Thread#interrupt interrupted},
* or the specified waiting time elapses.
*
*
* If the current count is zero then this method returns immediately with the value {@code true}.
*
*
* If the current count is greater than zero then the current thread becomes disabled for thread scheduling purposes and lies
* dormant until one of three things happen:
*
* - The count reaches zero due to invocations of the {@link #countDown} method; or
*
- Some other thread {@linkplain Thread#interrupt interrupts} the current thread; or
*
- The specified waiting time elapses.
*
*
*
* If the count reaches zero then the method returns with the value {@code true}.
*
*
* If the current thread:
*
* - has its interrupted status set on entry to this method; or
*
- is {@linkplain Thread#interrupt interrupted} while waiting,
*
* then {@link InterruptedException} is thrown and the current thread's interrupted status is cleared.
*
*
* If the specified waiting time elapses then the value {@code false} is returned. If the time is less than or equal to zero,
* the method will not wait at all.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the {@code timeout} argument
* @return {@code true} if the count reached zero and {@code false} if the waiting time elapsed before the count reached zero
* @throws InterruptedException if the current thread is interrupted
* while waiting
*/
public boolean await(long timeout, TimeUnit unit)
throws InterruptedException {
return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
}
/**
* Decrements the count of the latch, releasing all waiting threads if the count reaches zero.
*
*
* If the current count is greater than zero then it is decremented. If the new count is zero then all waiting threads are
* re-enabled for thread scheduling purposes.
*
*
* If the current count equals zero then nothing happens.
*/
public void countDown() {
sync.releaseShared(1);
}
/**
* Decrements the count of the latch, releasing all waiting threads if the count reaches zero.
*
*
* If the current count is greater than zero then it is decremented. If the new count is zero then all waiting threads are
* re-enabled for thread scheduling purposes.
*
*
* If the current count equals zero then nothing happens.
*
* @param count the number of counts to decrease
*/
public void countDown(int count) {
sync.releaseShared(1 * (Math.abs(count)));
}
/**
* Increments the count of the latch by one.
*/
public void countUp() {
sync.releaseShared(-1);
}
/**
* Increments the count of the latch by a positive number.
*
* @param count the number of counts to increase
*/
public void countUp(int count) {
sync.releaseShared(-1 * (Math.abs(count)));
}
/**
* Returns the current count.
*
*
* This method is typically used for debugging and testing purposes.
*
* @return the current count
*/
public long getCount() {
return sync.getCount();
}
/**
* Returns a string identifying this latch, as well as its state.
* The state, in brackets, includes the String {@code "Count ="} followed by the current count.
*
* @return a string identifying this latch, as well as its state
*/
@Override
public String toString() {
return super.toString() + "[Count = " + sync.getCount() + "]";
}
}