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A set of basic utilities used in Jitsi projects
/*
* Copyright @ 2018 - present 8x8, Inc.
*
* 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 org.jitsi.utils.queue;
import org.jetbrains.annotations.*;
import org.jitsi.utils.logging.*;
import java.util.concurrent.*;
/**
* Asynchronously reads items from provided {@link #queue} on separate thread
* borrowed from {@link #executor} and process items with specified handler.
* Thread is not blocked when queue is empty and returned back to
* {@link #executor} pool. New or existing thread is borrowed from
* {@link #executor} when queue is non empty and {@link #reader} is not
* running
*
* @author Yura Yaroshevich
*/
final class AsyncQueueHandler
{
/**
* The {@link java.util.logging.Logger} used by the
* {@link AsyncQueueHandler} class and its instances for logging output.
*/
private static final Logger logger
= Logger.getLogger(AsyncQueueHandler.class);
/**
* Executor service to run {@link #reader}, which asynchronously
* invokes specified {@link #handler} on queued items.
*/
private final ExecutorService executor;
/**
* An {@link BlockingQueue} whose items read on separate thread and
* processed by provided {@link #handler}.
*/
private final BlockingQueue queue;
/**
* The {@link Handler} used to handle items read from
* {@link #queue} by {@link #reader}.
*/
private final Handler handler;
/**
* An identifier of current reader which is used for debugging purpose.
*/
private final String id;
/**
* Specifies the number of items allowed to be handled sequentially
* without yielding control to executor's thread. Specifying positive
* number allows implementation of cooperative multi-tasking
* between different {@link AsyncQueueHandler} sharing
* same {@link ExecutorService}.
*/
private final long maxSequentiallyHandledItems;
/**
* A flag which indicates if reading of {@link #queue} is allowed
* to continue.
*/
private boolean running = true;
/**
* Synchronization object of current instance state, in particular
* used to resolve races between {@link #handleQueueItemsUntilEmpty()}
* and {@link #reader} exit. In particular synchronization object used to
* access to field {@link #readerFuture}.
*/
private final Object syncRoot = new Object();
/**
* Stores Future of currently executing {@link #reader}
*/
private Future readerFuture;
/**
* Whether canceling this {@link AsyncQueueHandler} is allowed to interrupt {@link #readerFuture} (if it's running).
*/
private final boolean interruptOnCancel;
/**
* Perpetually reads item from {@link #queue} and uses
* {@link #handler} on each of them.
*/
private final Runnable reader = new Runnable()
{
@Override
public void run()
{
long sequentiallyHandledItems = 0;
while (running)
{
if (maxSequentiallyHandledItems > 0 &&
sequentiallyHandledItems >= maxSequentiallyHandledItems)
{
onYield();
return;
}
T item;
synchronized (syncRoot)
{
item = queue.poll();
if (item == null)
{
cancel(false);
return;
}
}
sequentiallyHandledItems++;
try
{
handler.handleItem(item);
}
catch (Throwable e)
{
logger.error("Failed to handle item: ", e);
}
}
}
};
/**
* Constructs instance of {@link AsyncQueueHandler} which is capable of
* asynchronous reading provided queue from thread borrowed from executor to
* process items with provided handler.
* @param queue thread-safe queue which holds items to process
* @param handler an implementation of handler routine which will be
* invoked per each item placed in the queue.
* @param id optional identifier of current handler for debug purpose
* @param executor optional executor service to borrow threads from
* @param maxSequentiallyHandledItems maximum number of items sequentially
* handled on thread borrowed from {@link #executor} before temporary
* releasing thread and re-acquiring it from {@link #executor}.
*/
AsyncQueueHandler(
@NotNull BlockingQueue queue,
@NotNull Handler handler,
@NotNull String id,
@NotNull ExecutorService executor,
long maxSequentiallyHandledItems,
boolean interruptOnCancel)
{
this.executor = executor;
this.queue = queue;
this.handler = handler;
this.id = id;
this.maxSequentiallyHandledItems = maxSequentiallyHandledItems;
this.interruptOnCancel = interruptOnCancel;
}
/**
* Attempts to stop execution of {@link #reader} if running
*/
void cancel()
{
cancel(interruptOnCancel);
}
/**
* Checks if {@link #reader} is running on one of {@link #executor}
* thread and if no submits execution of {@link #reader} on executor.
*/
void handleQueueItemsUntilEmpty()
{
synchronized (syncRoot)
{
if (readerFuture == null || readerFuture.isDone())
{
rescheduleReader();
}
}
}
/**
* Invoked when execution of {@link #reader} is about to temporary
* cancel and further execution need to be re-scheduled.
*/
private void onYield()
{
if (logger.isDebugEnabled())
{
logger.debug("Yielding AsyncQueueHandler with ID = " + id);
}
rescheduleReader();
}
/**
* Attempts to cancel currently running reader.
* @param mayInterruptIfRunning indicates if {@link #reader} allowed
* to be interrupted if running
*/
private void cancel(boolean mayInterruptIfRunning)
{
synchronized (syncRoot)
{
running = false;
if (readerFuture != null)
{
readerFuture.cancel(mayInterruptIfRunning);
readerFuture = null;
}
}
}
/**
* Reschedules execution of {@link #reader} on {@link #executor}'s thread.
*/
private void rescheduleReader()
{
synchronized (syncRoot)
{
running = true;
readerFuture = executor.submit(reader);
}
}
/**
* A simple interface to handle enqueued {@link T} items.
* @param the type of the item.
*/
interface Handler
{
/**
* Does something with an item.
* @param item the item to do something with.
*/
void handleItem(T item);
}
}