org.glassfish.grizzly.comet.concurrent.DefaultConcurrentCometHandler Maven / Gradle / Ivy
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package org.glassfish.grizzly.comet.concurrent;
import java.io.IOException;
import java.util.LinkedList;
import java.util.Queue;
import java.util.logging.Logger;
import org.glassfish.grizzly.comet.CometContext;
import org.glassfish.grizzly.comet.CometEvent;
import org.glassfish.grizzly.comet.CometHandler;
import org.glassfish.grizzly.http.server.Response;
/**
* We queue events in each CometHandler to lower the probability that slow or massive IO for one CometHandler severely
* delays events to others.
only streaming mode can benefit from buffering messages like this.
only 1
* thread at a time is allowed to do IO, other threads put events in the queue and return to the thread pool.
a
* thread initially calls enqueueEvent and stay there until there are no more events in the queue, calling the onEVent
* method in synchronized context for each Event.
on IOE in onEvent we terminate.
we have a limit, to keep
* memory usage under control.
if queue limit is reached onQueueFull is called, and then we terminate.
*
whats not optimal is that a worker thread is sticky to the client depending upon available events in the
* handlers local queue, that can in theory allow a few clients to block all threads for extended time.
that effect
* can make this implementation unusable depending on the scenario, its not a perfect design be any means.
The
* potential improvement is that only 1 worker thread is tied up to a client instead of several being blocked by
* synchronized io wait for one CometHandler .
*
* @author Gustav Trede
*/
public abstract class DefaultConcurrentCometHandler implements CometHandler {
protected final static Logger logger = Logger.getLogger(DefaultConcurrentCometHandler.class.getName());
/**
* used for preventing the worker threads from the executor event queue from adding events to the comet handlers
* local queue or starting IO logic after shut down.
*/
private boolean shuttingDown;
/**
* max number of events to locally queue for this CometHandler.
(a global event queue normally exists in form of
* a thread pool too)
*/
private final int messageQueueLimit;
/**
* current queue size
*/
private int queueSize;
/**
* true means that no thread is currently active on this comet handlers queue logic
*/
private boolean readyForWork = true;
/**
* todo replace with non array copying list for non resizing add situations, using internal index to keep track of
* state , not a linked list, it has too much overhead and eats memory.
*/
protected final Queue messageQueue = new LinkedList();
private CometContext context;
private Response response;
public DefaultConcurrentCometHandler(final CometContext context, final Response response) {
this(100);
this.context = context;
this.response = response;
}
/**
* @param messageQueueLimit
*/
public DefaultConcurrentCometHandler(int messageQueueLimit) {
this.messageQueueLimit = messageQueueLimit;
}
@Override
public CometContext getCometContext() {
return context;
}
@Override
public void setCometContext(final CometContext context) {
this.context = context;
}
@Override
public Response getResponse() {
return response;
}
@Override
public void setResponse(final Response response) {
this.response = response;
}
/**
* Queues event if another thread is currently working on this handler. The first thread to start working will keep
* doing so until there are no further events in the internal queue.
*/
public void enqueueEvent(CometEvent event) throws IOException {
synchronized (messageQueue) {
if (!readyForWork) {
if (!shuttingDown && queueSize < messageQueueLimit) {
messageQueue.add(event);
queueSize++;
}
return;
}
readyForWork = false;
}
boolean queueFull = false;
while (!shuttingDown) {
if (!event.getCometContext().isActive(this)) {
shuttingDown = true;
return;
}
try {
//move synchronized outside the while loop ?
synchronized (this) {
onEvent(event);
}
} catch (IOException ex) {
shuttingDown = true;
} finally {
if (shuttingDown) {
event.getCometContext().resumeCometHandler(this);
return;
}
}
synchronized (messageQueue) {
if (queueSize == messageQueueLimit) {
queueFull = true;
} else if (queueSize == 0) {
readyForWork = true;
return;
} else {
event = messageQueue.poll();
queueSize--;
}
}
if (queueFull) {
shuttingDown = true;
// todo is onQueueFull needed ? or just terminate, it would simplify to just terminate =)
onQueueFull(event);
}
}
}
/**
* Called in synchronized context when the comet handler's local event queue is full.
default impl resumes the
* comet handler
*
* @param event {@link CometEvent}
*/
public void onQueueFull(CometEvent event) throws IOException {
event.getCometContext().resumeCometHandler(this);
}
/**
* {@inheritDoc}
default impl calls terminate()
*/
public void onInterrupt(CometEvent event) throws IOException {
terminate();
}
/**
* {@inheritDoc}
default impl calls terminate()
*/
public void onTerminate(CometEvent event) throws IOException {
terminate();
}
protected void terminate() {
}
}