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// Copyright 2017 The Bazel Authors. All rights reserved.
//
// 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.devtools.build.lib.buildeventstream.transports;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;
import com.google.devtools.build.lib.buildeventstream.BuildEvent;
import com.google.devtools.build.lib.buildeventstream.BuildEventTransport;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.channels.CompletionHandler;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.concurrent.Future;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* Non-blocking file transport.
*
* <p>Implementors of this class need to implement {@link #sendBuildEvent(BuildEvent)} which
* serializes the build event and writes it to file using {@link #writeData(byte[])}.
*/
abstract class FileTransport implements BuildEventTransport {
/**
* We use an {@link AsynchronousFileChannel} to perform non-blocking writes to a file. It get's
* tricky when it comes to {@link #close()}, as we may only complete the returned future when
* all writes have completed (succeeded or failed). Thus, we use a field
* {@link #outstandingWrites} to keep track of the number of writes that have not completed yet.
* It's simply incremented before a new write and decremented after a write has completed. When
* it's {@code 0} it's safe to complete the close future.
*/
private static final Logger log = Logger.getLogger(FileTransport.class.getName());
@VisibleForTesting
final AsynchronousFileChannel ch;
private final WriteCompletionHandler completionHandler = new WriteCompletionHandler();
// The offset in the file to begin the next write at.
private long writeOffset;
// Number of writes that haven't completed yet.
private long outstandingWrites;
// The future returned by close()
private SettableFuture<Void> closeFuture;
FileTransport(String path) {
try {
ch = AsynchronousFileChannel.open(Paths.get(path), StandardOpenOption.CREATE,
StandardOpenOption.TRUNCATE_EXISTING, StandardOpenOption.WRITE);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
synchronized void writeData(byte[] data) {
checkNotNull(data);
if (!ch.isOpen()) {
@SuppressWarnings({"unused", "nullness"})
Future<?> possiblyIgnoredError = close();
return;
}
if (closing()) {
return;
}
outstandingWrites++;
ch.write(ByteBuffer.wrap(data), writeOffset, null, completionHandler);
writeOffset += data.length;
}
@Override
public synchronized ListenableFuture<Void> close() {
if (closing()) {
return closeFuture;
}
closeFuture = SettableFuture.create();
if (writesComplete()) {
doClose();
}
return closeFuture;
}
private void doClose() {
try {
ch.force(true);
ch.close();
} catch (IOException e) {
log.log(Level.SEVERE, e.getMessage(), e);
} finally {
closeFuture.set(null);
}
}
private boolean closing() {
return closeFuture != null;
}
private boolean writesComplete() {
return outstandingWrites == 0;
}
/**
* Handler that's notified when a write completes.
*/
private final class WriteCompletionHandler implements CompletionHandler<Integer, Void> {
@Override
public void completed(Integer result, Void attachment) {
countWriteAndTryClose();
}
@Override
public void failed(Throwable exc, Void attachment) {
log.log(Level.SEVERE, exc.getMessage(), exc);
countWriteAndTryClose();
// There is no point in trying to continue. Close the transport.
@SuppressWarnings({"unused", "nullness"})
Future<?> possiblyIgnoredError = close();
}
private void countWriteAndTryClose() {
synchronized (FileTransport.this) {
checkState(outstandingWrites > 0);
outstandingWrites--;
if (closing() && writesComplete()) {
doClose();
}
}
}
}
}
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