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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jrt;
/**
* A thread-safe queue wrapper used to pass objects between threads.
**/
class ThreadQueue
{
private Queue queue = new Queue();
private boolean closed = false;
public ThreadQueue() {}
/**
* Enqueue an object on this queue. If the queue has been closed,
* the object will not be queued, and this method will return
* false.
*
* @return true if the object was enqueued, false if this queue
* was closed
* @param obj the object to enqueue
**/
public boolean enqueue(Object obj) {
return enqueue(obj, Integer.MAX_VALUE);
}
/**
* Enqueue an object on this queue. If the queue has been closed or
* the queue already contains too many items, the object will not be
* queued, and this method will return false.
*
* @return true if the object was enqueued, false if this queue
* was closed or too large
* @param obj the object to enqueue
* @param limit more elements than this means the queue is too large
**/
public synchronized boolean enqueue(Object obj, int limit) {
if (closed || (queue.size() > limit)) {
return false;
}
queue.enqueue(obj);
if (queue.size() == 1) {
notify(); // assume only one reader
}
return true;
}
/**
* Close this queue. After this method is invoked, no more objects
* may be enqueued on this queue. Also, trying to dequeue an
* object form a queue that is both empty and closed will cause a
* {@link EndOfQueueException}.
**/
public synchronized void close() {
closed = true;
notify();
}
/**
* Dequeue the next object from this queue. This method will block
* until at least one object is available in the queue.
*
* @return the next object from the queue
* @throws EndOfQueueException if the queue is both empty and
* closed
**/
public synchronized Object dequeue() throws EndOfQueueException {
while (queue.isEmpty() && !closed) {
try { wait(); } catch (InterruptedException x) {}
}
if (queue.isEmpty()) {
throw new EndOfQueueException();
}
return queue.dequeue();
}
}
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