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A module that is everything required to understands Druid Segments
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.druid.frame.channel;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import org.apache.druid.frame.Frame;
import org.apache.druid.java.util.common.Either;
import org.apache.druid.java.util.common.IAE;
import org.apache.druid.java.util.common.ISE;
import javax.annotation.Nullable;
import java.util.ArrayDeque;
import java.util.NoSuchElementException;
import java.util.Optional;
/**
* In-memory channel backed by a limited-capacity {@link java.util.Deque}.
*
* Instances of this class provide a {@link ReadableFrameChannel} through {@link #readable()}, and a
* {@link WritableFrameChannel} through {@link #writable()}. Instances of this class are used by a single writer
* and single reader. The writer and reader may run concurrently.
*/
public class BlockingQueueFrameChannel
{
@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
private static final Optional> END_MARKER = Optional.empty();
private final int maxQueuedFrames;
private final Object lock = new Object();
private final Writable writable;
private final Readable readable;
@GuardedBy("lock")
private final ArrayDeque>> queue;
@GuardedBy("lock")
private SettableFuture readyForWritingFuture = null;
@GuardedBy("lock")
private SettableFuture readyForReadingFuture = null;
/**
* Create a channel with a particular buffer size (expressed in number of frames).
*/
public BlockingQueueFrameChannel(final int maxQueuedFrames)
{
if (maxQueuedFrames < 1 || maxQueuedFrames == Integer.MAX_VALUE) {
throw new IAE("Cannot handle capacity of [%d]", maxQueuedFrames);
}
this.maxQueuedFrames = maxQueuedFrames;
this.queue = new ArrayDeque<>(maxQueuedFrames + 1); // Plus one to leave space for END_MARKER.
this.writable = new Writable();
this.readable = new Readable();
}
/**
* Returns the writable side of this channel.
*/
public WritableFrameChannel writable()
{
return writable;
}
/**
* Returns the readable side of this channel.
*/
public ReadableFrameChannel readable()
{
return readable;
}
/**
* Create a channel that buffers one frame. This is the smallest possible queue size.
*/
public static BlockingQueueFrameChannel minimal()
{
return new BlockingQueueFrameChannel(1);
}
private boolean isFinished()
{
synchronized (lock) {
return END_MARKER.equals(queue.peek());
}
}
@GuardedBy("lock")
private void notifyWriter()
{
if (readyForWritingFuture != null) {
final SettableFuture tmp = readyForWritingFuture;
this.readyForWritingFuture = null;
tmp.set(null);
}
}
@GuardedBy("lock")
private void notifyReader()
{
if (readyForReadingFuture != null) {
final SettableFuture tmp = readyForReadingFuture;
this.readyForReadingFuture = null;
tmp.set(null);
}
}
private class Writable implements WritableFrameChannel
{
@Override
public void write(FrameWithPartition frame)
{
synchronized (lock) {
if (isFinished()) {
throw new ISE("Channel cannot accept new frames");
} else if (queue.size() >= maxQueuedFrames) {
// Caller should have checked if this channel was ready for writing.
throw new ISE("Channel has no capacity");
} else {
if (!queue.offer(Optional.of(Either.value(frame)))) {
// If this happens, it's a bug in this class's capacity-counting.
throw new ISE("Channel had capacity, but could not add frame");
}
}
notifyReader();
}
}
@Override
public ListenableFuture writabilityFuture()
{
synchronized (lock) {
if (queue.size() < maxQueuedFrames) {
return Futures.immediateFuture(null);
} else if (readyForWritingFuture != null) {
return readyForWritingFuture;
} else {
return (readyForWritingFuture = SettableFuture.create());
}
}
}
@Override
public void fail(@Nullable Throwable cause)
{
synchronized (lock) {
queue.clear();
if (!queue.offer(Optional.of(Either.error(cause != null ? cause : new ISE("Failed"))))) {
// If this happens, it's a bug, potentially due to incorrectly using this class with multiple writers.
throw new ISE("Could not write error to channel");
}
}
}
@Override
public void close()
{
synchronized (lock) {
if (isClosed()) {
throw new ISE("Already closed");
}
if (!queue.offer(END_MARKER)) {
// If this happens, it's a bug, potentially due to incorrectly using this class with multiple writers.
throw new ISE("Channel had capacity, but could not add end marker");
}
notifyReader();
}
}
@Override
public boolean isClosed()
{
synchronized (lock) {
final Optional> lastElement = queue.peekLast();
return lastElement != null && END_MARKER.equals(lastElement);
}
}
}
private class Readable implements ReadableFrameChannel
{
@Override
public boolean isFinished()
{
return BlockingQueueFrameChannel.this.isFinished();
}
@Override
public boolean canRead()
{
synchronized (lock) {
return !queue.isEmpty() && !isFinished();
}
}
@Override
public Frame read()
{
final Optional> next;
synchronized (lock) {
if (isFinished()) {
throw new NoSuchElementException();
}
next = queue.poll();
if (next == null || !next.isPresent()) {
throw new NoSuchElementException();
}
notifyWriter();
}
return next.get().valueOrThrow().frame();
}
@Override
public ListenableFuture readabilityFuture()
{
synchronized (lock) {
if (!queue.isEmpty()) {
return Futures.immediateFuture(null);
} else if (readyForReadingFuture != null) {
return readyForReadingFuture;
} else {
return (readyForReadingFuture = SettableFuture.create());
}
}
}
@Override
public void close()
{
synchronized (lock) {
queue.clear();
notifyWriter();
}
}
}
}