io.sentry.transport.ReusableCountLatch Maven / Gradle / Ivy
/*
* Adapted from https://github.com/MatejTymes/JavaFixes/blob/37e74b9d0a29f7a47485c6d1bb1307f01fb93634/src/main/java/javafixes/concurrency/ReusableCountLatch.java
*
* Copyright (C) 2016 Matej Tymes
*
* Licensed 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 io.sentry.transport;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import org.jetbrains.annotations.NotNull;
/**
* A synchronization aid that allows one or more threads to wait until a set of operations being
* performed in other threads completes.
*
* A {@code ReusableCountLatch} is initialized with a given count. The {@link
* #waitTillZero} methods block until the current count reaches zero due to invocations of the
* {@link #decrement} method, after which all waiting threads are released. If zero has been reached
* any subsequent invocations of {@link #waitTillZero} return immediately. The count can be
* increased calling the {@link #increment()} method and any subsequent thread calling the {@link
* #waitTillZero} method will be blocked again until another zero is reached.
*
*
{@code ReusableCountLatch} provides more versatility than {@link
* java.util.concurrent.CountDownLatch CountDownLatch} as the count doesn't have to be known upfront
* and you can reuse this class as many times as you want to. It is also better than a {@link
* java.util.concurrent.Phaser Phaser} whose count is limited to 65_535. {@code ReusableCountLatch}
* instead can count up to 2_147_483_647 (2^31-1).
*
*
Great use case for {@code ReusableCountLatch} is when you wait for tasks on other threads to
* finish, but these tasks could trigger more tasks and it is not known upfront how many will be
* triggered in total.
*
* @author mtymes
* @since 07/10/16 00:10 AM
*/
public final class ReusableCountLatch {
private final @NotNull Sync sync;
/**
* Constructs a {@code ReusableCountLatch} initialized with the given count.
*
* @param initialCount the number of times {@link #decrement} must be invoked before threads can
* pass through {@link #waitTillZero}. For each additional call of the {@link #increment}
* method one more {@link #decrement} must be called.
* @throws IllegalArgumentException if {@code initialCount} is negative
*/
public ReusableCountLatch(final int initialCount) {
if (initialCount < 0) {
throw new IllegalArgumentException(
"negative initial count '" + initialCount + "' is not allowed");
}
this.sync = new Sync(initialCount);
}
/** Constructs a {@code ReusableCountLatch} with initial count set to 0. */
public ReusableCountLatch() {
this(0);
}
/**
* Returns the current count.
*
* @return the current count
*/
public int getCount() {
return sync.getCount();
}
/**
* 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 decrement() {
sync.decrement();
}
/**
* Increments the count of the latch, which will make it possible to block all threads waiting
* till count reaches zero.
*/
public void increment() {
sync.increment();
}
/**
* 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 #decrement} 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 waitTillZero() 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 #decrement()} 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 waitTillZero(final long timeout, final @NotNull TimeUnit unit)
throws InterruptedException {
return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
}
/** Synchronization control For ReusableCountLatch. Uses AQS state to represent count. */
private static final class Sync extends AbstractQueuedSynchronizer {
private static final long serialVersionUID = 5970133580157457018L;
Sync(final int count) {
setState(count);
}
private int getCount() {
return getState();
}
private void increment() {
for (; ; ) {
int oldCount = getState();
int newCount = oldCount + 1;
if (compareAndSetState(oldCount, newCount)) {
return;
}
}
}
private void decrement() {
releaseShared(1);
}
@Override
public int tryAcquireShared(final int acquires) {
return (getState() == 0) ? 1 : -1;
}
@Override
public boolean tryReleaseShared(final int releases) {
// Decrement count; signal when transition to zero
for (; ; ) {
int oldCount = getState();
if (oldCount == 0) {
return false;
}
int newCount = oldCount - 1;
if (compareAndSetState(oldCount, newCount)) {
return newCount == 0;
}
}
}
}
}