com.google.common.collect.Queues Maven / Gradle / Ivy
/*
* Copyright (C) 2011 The Guava Authors
*
* 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 com.google.common.collect;
import com.google.common.annotations.Beta;
import com.google.common.base.Preconditions;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Deque;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.PriorityBlockingQueue;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;
/**
* Static utility methods pertaining to {@link Queue} and {@link Deque} instances.
* Also see this class's counterparts {@link Lists}, {@link Sets}, and {@link Maps}.
*
* @author Kurt Alfred Kluever
* @since 11.0
*/
public final class Queues {
private Queues() {}
// ArrayBlockingQueue
/**
* Creates an empty {@code ArrayBlockingQueue} with the given (fixed) capacity
* and nonfair access policy.
*/
public static ArrayBlockingQueue newArrayBlockingQueue(int capacity) {
return new ArrayBlockingQueue(capacity);
}
// ArrayDeque
/**
* Creates an empty {@code ArrayDeque}.
*
* @since 12.0
*/
public static ArrayDeque newArrayDeque() {
return new ArrayDeque();
}
/**
* Creates an {@code ArrayDeque} containing the elements of the specified iterable,
* in the order they are returned by the iterable's iterator.
*
* @since 12.0
*/
public static ArrayDeque newArrayDeque(Iterable elements) {
if (elements instanceof Collection) {
return new ArrayDeque(Collections2.cast(elements));
}
ArrayDeque deque = new ArrayDeque();
Iterables.addAll(deque, elements);
return deque;
}
// ConcurrentLinkedQueue
/**
* Creates an empty {@code ConcurrentLinkedQueue}.
*/
public static ConcurrentLinkedQueue newConcurrentLinkedQueue() {
return new ConcurrentLinkedQueue();
}
/**
* Creates a {@code ConcurrentLinkedQueue} containing the elements of the specified iterable,
* in the order they are returned by the iterable's iterator.
*/
public static ConcurrentLinkedQueue newConcurrentLinkedQueue(
Iterable elements) {
if (elements instanceof Collection) {
return new ConcurrentLinkedQueue(Collections2.cast(elements));
}
ConcurrentLinkedQueue queue = new ConcurrentLinkedQueue();
Iterables.addAll(queue, elements);
return queue;
}
// LinkedBlockingDeque
/**
* Creates an empty {@code LinkedBlockingDeque} with a capacity of {@link Integer#MAX_VALUE}.
*
* @since 12.0
*/
public static LinkedBlockingDeque newLinkedBlockingDeque() {
return new LinkedBlockingDeque();
}
/**
* Creates an empty {@code LinkedBlockingDeque} with the given (fixed) capacity.
*
* @throws IllegalArgumentException if {@code capacity} is less than 1
* @since 12.0
*/
public static LinkedBlockingDeque newLinkedBlockingDeque(int capacity) {
return new LinkedBlockingDeque(capacity);
}
/**
* Creates a {@code LinkedBlockingDeque} with a capacity of {@link Integer#MAX_VALUE},
* containing the elements of the specified iterable,
* in the order they are returned by the iterable's iterator.
*
* @since 12.0
*/
public static LinkedBlockingDeque newLinkedBlockingDeque(Iterable elements) {
if (elements instanceof Collection) {
return new LinkedBlockingDeque(Collections2.cast(elements));
}
LinkedBlockingDeque deque = new LinkedBlockingDeque();
Iterables.addAll(deque, elements);
return deque;
}
// LinkedBlockingQueue
/**
* Creates an empty {@code LinkedBlockingQueue} with a capacity of {@link Integer#MAX_VALUE}.
*/
public static LinkedBlockingQueue newLinkedBlockingQueue() {
return new LinkedBlockingQueue();
}
/**
* Creates an empty {@code LinkedBlockingQueue} with the given (fixed) capacity.
*
* @throws IllegalArgumentException if {@code capacity} is less than 1
*/
public static LinkedBlockingQueue newLinkedBlockingQueue(int capacity) {
return new LinkedBlockingQueue(capacity);
}
/**
* Creates a {@code LinkedBlockingQueue} with a capacity of {@link Integer#MAX_VALUE},
* containing the elements of the specified iterable,
* in the order they are returned by the iterable's iterator.
*
* @param elements the elements that the queue should contain, in order
* @return a new {@code LinkedBlockingQueue} containing those elements
*/
public static LinkedBlockingQueue newLinkedBlockingQueue(Iterable elements) {
if (elements instanceof Collection) {
return new LinkedBlockingQueue(Collections2.cast(elements));
}
LinkedBlockingQueue queue = new LinkedBlockingQueue();
Iterables.addAll(queue, elements);
return queue;
}
// LinkedList: see {@link com.google.common.collect.Lists}
// PriorityBlockingQueue
/**
* Creates an empty {@code PriorityBlockingQueue} with the ordering given by its
* elements' natural ordering.
*
* @since 11.0 (requires that {@code E} be {@code Comparable} since 15.0).
*/
public static PriorityBlockingQueue newPriorityBlockingQueue() {
return new PriorityBlockingQueue();
}
/**
* Creates a {@code PriorityBlockingQueue} containing the given elements.
*
* Note: If the specified iterable is a {@code SortedSet} or a {@code PriorityQueue},
* this priority queue will be ordered according to the same ordering.
*
* @since 11.0 (requires that {@code E} be {@code Comparable} since 15.0).
*/
public static PriorityBlockingQueue newPriorityBlockingQueue(
Iterable elements) {
if (elements instanceof Collection) {
return new PriorityBlockingQueue(Collections2.cast(elements));
}
PriorityBlockingQueue queue = new PriorityBlockingQueue();
Iterables.addAll(queue, elements);
return queue;
}
// PriorityQueue
/**
* Creates an empty {@code PriorityQueue} with the ordering given by its
* elements' natural ordering.
*
* @since 11.0 (requires that {@code E} be {@code Comparable} since 15.0).
*/
public static PriorityQueue newPriorityQueue() {
return new PriorityQueue();
}
/**
* Creates a {@code PriorityQueue} containing the given elements.
*
* Note: If the specified iterable is a {@code SortedSet} or a {@code PriorityQueue},
* this priority queue will be ordered according to the same ordering.
*
* @since 11.0 (requires that {@code E} be {@code Comparable} since 15.0).
*/
public static PriorityQueue newPriorityQueue(
Iterable elements) {
if (elements instanceof Collection) {
return new PriorityQueue(Collections2.cast(elements));
}
PriorityQueue queue = new PriorityQueue();
Iterables.addAll(queue, elements);
return queue;
}
// SynchronousQueue
/**
* Creates an empty {@code SynchronousQueue} with nonfair access policy.
*/
public static SynchronousQueue newSynchronousQueue() {
return new SynchronousQueue();
}
/**
* Drains the queue as {@link BlockingQueue#drainTo(Collection, int)}, but if the requested
* {@code numElements} elements are not available, it will wait for them up to the specified
* timeout.
*
* @param q the blocking queue to be drained
* @param buffer where to add the transferred elements
* @param numElements the number of elements to be waited for
* @param timeout how long to wait before giving up, in units of {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the timeout parameter
* @return the number of elements transferred
* @throws InterruptedException if interrupted while waiting
*/
@Beta
public static int drain(BlockingQueue q, Collection buffer, int numElements,
long timeout, TimeUnit unit) throws InterruptedException {
Preconditions.checkNotNull(buffer);
/*
* This code performs one System.nanoTime() more than necessary, and in return, the time to
* execute Queue#drainTo is not added *on top* of waiting for the timeout (which could make
* the timeout arbitrarily inaccurate, given a queue that is slow to drain).
*/
long deadline = System.nanoTime() + unit.toNanos(timeout);
int added = 0;
while (added < numElements) {
// we could rely solely on #poll, but #drainTo might be more efficient when there are multiple
// elements already available (e.g. LinkedBlockingQueue#drainTo locks only once)
added += q.drainTo(buffer, numElements - added);
if (added < numElements) { // not enough elements immediately available; will have to poll
E e = q.poll(deadline - System.nanoTime(), TimeUnit.NANOSECONDS);
if (e == null) {
break; // we already waited enough, and there are no more elements in sight
}
buffer.add(e);
added++;
}
}
return added;
}
/**
* Drains the queue as {@linkplain #drain(BlockingQueue, Collection, int, long, TimeUnit)},
* but with a different behavior in case it is interrupted while waiting. In that case, the
* operation will continue as usual, and in the end the thread's interruption status will be set
* (no {@code InterruptedException} is thrown).
*
* @param q the blocking queue to be drained
* @param buffer where to add the transferred elements
* @param numElements the number of elements to be waited for
* @param timeout how long to wait before giving up, in units of {@code unit}
* @param unit a {@code TimeUnit} determining how to interpret the timeout parameter
* @return the number of elements transferred
*/
@Beta
public static int drainUninterruptibly(BlockingQueue q, Collection buffer,
int numElements, long timeout, TimeUnit unit) {
Preconditions.checkNotNull(buffer);
long deadline = System.nanoTime() + unit.toNanos(timeout);
int added = 0;
boolean interrupted = false;
try {
while (added < numElements) {
// we could rely solely on #poll, but #drainTo might be more efficient when there are
// multiple elements already available (e.g. LinkedBlockingQueue#drainTo locks only once)
added += q.drainTo(buffer, numElements - added);
if (added < numElements) { // not enough elements immediately available; will have to poll
E e; // written exactly once, by a successful (uninterrupted) invocation of #poll
while (true) {
try {
e = q.poll(deadline - System.nanoTime(), TimeUnit.NANOSECONDS);
break;
} catch (InterruptedException ex) {
interrupted = true; // note interruption and retry
}
}
if (e == null) {
break; // we already waited enough, and there are no more elements in sight
}
buffer.add(e);
added++;
}
}
} finally {
if (interrupted) {
Thread.currentThread().interrupt();
}
}
return added;
}
/**
* Returns a synchronized (thread-safe) queue backed by the specified queue. In order to
* guarantee serial access, it is critical that all access to the backing queue is
* accomplished through the returned queue.
*
* It is imperative that the user manually synchronize on the returned queue when accessing
* the queue's iterator:
{@code
*
* Queue queue = Queues.synchronizedQueue(MinMaxPriorityQueue.create());
* ...
* queue.add(element); // Needn't be in synchronized block
* ...
* synchronized (queue) { // Must synchronize on queue!
* Iterator i = queue.iterator(); // Must be in synchronized block
* while (i.hasNext()) {
* foo(i.next());
* }
* }}
*
* Failure to follow this advice may result in non-deterministic behavior.
*
*
The returned queue will be serializable if the specified queue is serializable.
*
* @param queue the queue to be wrapped in a synchronized view
* @return a synchronized view of the specified queue
* @since 14.0
*/
public static Queue synchronizedQueue(Queue queue) {
return Synchronized.queue(queue, null);
}
/**
* Returns a synchronized (thread-safe) deque backed by the specified deque. In order to
* guarantee serial access, it is critical that all access to the backing deque is
* accomplished through the returned deque.
*
* It is imperative that the user manually synchronize on the returned deque when accessing
* any of the deque's iterators:
{@code
*
* Deque deque = Queues.synchronizedDeque(Queues.newArrayDeque());
* ...
* deque.add(element); // Needn't be in synchronized block
* ...
* synchronized (deque) { // Must synchronize on deque!
* Iterator i = deque.iterator(); // Must be in synchronized block
* while (i.hasNext()) {
* foo(i.next());
* }
* }}
*
* Failure to follow this advice may result in non-deterministic behavior.
*
*
The returned deque will be serializable if the specified deque is serializable.
*
* @param deque the deque to be wrapped in a synchronized view
* @return a synchronized view of the specified deque
* @since 15.0
*/
public static Deque synchronizedDeque(Deque deque) {
return Synchronized.deque(deque, null);
}
}
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