// Copyright (C) 2010 The Android Open Source Project
//
// 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.gerrit.sshd.commands;
import com.google.gerrit.common.ChangeHooks;
import com.google.gerrit.common.ChangeListener;
import com.google.gerrit.server.IdentifiedUser;
import com.google.gerrit.server.events.ChangeEvent;
import com.google.gerrit.server.git.WorkQueue;
import com.google.gerrit.server.git.WorkQueue.CancelableRunnable;
import com.google.gerrit.sshd.BaseCommand;
import com.google.gerrit.sshd.StreamCommandExecutor;
import com.google.gson.Gson;
import com.google.inject.Inject;
import org.apache.sshd.server.Environment;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
final class StreamEvents extends BaseCommand {
/** Maximum number of events that may be queued up for each connection. */
private static final int MAX_EVENTS = 128;
/** Number of events to write before yielding off the thread. */
private static final int BATCH_SIZE = 32;
@Inject
private IdentifiedUser currentUser;
@Inject
private ChangeHooks hooks;
@Inject
@StreamCommandExecutor
private WorkQueue.Executor pool;
/** Queue of events to stream to the connected user. */
private final LinkedBlockingQueue<ChangeEvent> queue =
new LinkedBlockingQueue<ChangeEvent>(MAX_EVENTS);
private final Gson gson = new Gson();
/** Special event to notify clients they missed other events. */
private final Object droppedOutputEvent = new Object() {
@SuppressWarnings("unused")
final String type = "dropped-output";
};
private final ChangeListener listener = new ChangeListener() {
@Override
public void onChangeEvent(final ChangeEvent event) {
offer(event);
}
};
private final CancelableRunnable writer = new CancelableRunnable() {
@Override
public void run() {
writeEvents();
}
@Override
public void cancel() {
onExit(0);
}
};
/** True if {@link #droppedOutputEvent} needs to be sent. */
private volatile boolean dropped;
/** Lock to protect {@link #queue}, {@link #task}, {@link #done}. */
private final Object taskLock = new Object();
/** True if no more messages should be sent to the output. */
private boolean done;
/**
* Currently scheduled task to spin out {@link #queue}.
* <p>
* This field is usually {@code null}, unless there is at least one object
* present inside of {@link #queue} ready for delivery. Tasks are only started
* when there are events to be sent.
*/
private Future<?> task;
private PrintWriter stdout;
@Override
public void start(final Environment env) throws IOException {
try {
parseCommandLine();
} catch (UnloggedFailure e) {
String msg = e.getMessage();
if (!msg.endsWith("\n")) {
msg += "\n";
}
err.write(msg.getBytes("UTF-8"));
err.flush();
onExit(1);
return;
}
stdout = toPrintWriter(out);
hooks.addChangeListener(listener, currentUser);
}
@Override
protected void onExit(final int rc) {
hooks.removeChangeListener(listener);
synchronized (taskLock) {
done = true;
}
super.onExit(rc);
}
@Override
public void destroy() {
hooks.removeChangeListener(listener);
final boolean exit;
synchronized (taskLock) {
if (task != null) {
task.cancel(true);
exit = false; // onExit will be invoked by the task cancellation.
} else {
exit = !done;
}
done = true;
}
if (exit) {
onExit(0);
}
}
private void offer(final ChangeEvent event) {
synchronized (taskLock) {
if (!queue.offer(event)) {
dropped = true;
}
if (task == null && !done) {
task = pool.submit(writer);
}
}
}
private ChangeEvent poll() {
synchronized (taskLock) {
ChangeEvent event = queue.poll();
if (event == null) {
task = null;
}
return event;
}
}
private void writeEvents() {
int processed = 0;
while (processed < BATCH_SIZE) {
if (Thread.interrupted() || stdout.checkError()) {
// The other side either requested a shutdown by calling our
// destroy() above, or it closed the stream and is no longer
// accepting output. Either way terminate this instance.
//
hooks.removeChangeListener(listener);
flush();
onExit(0);
return;
}
if (dropped) {
write(droppedOutputEvent);
dropped = false;
}
final ChangeEvent event = poll();
if (event == null) {
break;
}
write(event);
processed++;
}
flush();
if (BATCH_SIZE <= processed) {
// We processed the limit, but more might remain in the queue.
// Schedule the write task again so we will come back here and
// can process more events.
//
synchronized (taskLock) {
task = pool.submit(writer);
}
}
}
private void write(final Object message) {
final String msg = gson.toJson(message) + "\n";
synchronized (stdout) {
stdout.print(msg);
}
}
private void flush() {
synchronized (stdout) {
stdout.flush();
}
}
}