/*
* Copyright 2015 The Netty Project
*
* The Netty Project 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 io.netty.handler.codec.http2;
import io.netty.util.internal.UnstableApi;
import java.util.ArrayDeque;
import java.util.Deque;
import static io.netty.handler.codec.http2.Http2CodecUtil.DEFAULT_MIN_ALLOCATION_CHUNK;
import static io.netty.handler.codec.http2.Http2CodecUtil.streamableBytes;
import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
import static io.netty.handler.codec.http2.Http2Exception.connectionError;
import static io.netty.util.internal.ObjectUtil.checkNotNull;
import static java.lang.Math.max;
import static java.lang.Math.min;
/**
* A {@link StreamByteDistributor} that ignores stream priority and uniformly allocates bytes to all
* streams. This class uses a minimum chunk size that will be allocated to each stream. While
* fewer streams may be written to in each call to {@link #distribute(int, Writer)}, doing this
* should improve the goodput on each written stream.
*/
@UnstableApi
public final class UniformStreamByteDistributor implements StreamByteDistributor {
private final Http2Connection.PropertyKey stateKey;
private final Deque<State> queue = new ArrayDeque<State>(4);
/**
* The minimum number of bytes that we will attempt to allocate to a stream. This is to
* help improve goodput on a per-stream basis.
*/
private int minAllocationChunk = DEFAULT_MIN_ALLOCATION_CHUNK;
private long totalStreamableBytes;
public UniformStreamByteDistributor(Http2Connection connection) {
// Add a state for the connection.
stateKey = connection.newKey();
Http2Stream connectionStream = connection.connectionStream();
connectionStream.setProperty(stateKey, new State(connectionStream));
// Register for notification of new streams.
connection.addListener(new Http2ConnectionAdapter() {
@Override
public void onStreamAdded(Http2Stream stream) {
stream.setProperty(stateKey, new State(stream));
}
@Override
public void onStreamClosed(Http2Stream stream) {
state(stream).close();
}
});
}
/**
* Sets the minimum allocation chunk that will be allocated to each stream. Defaults to 1KiB.
*
* @param minAllocationChunk the minimum number of bytes that will be allocated to each stream.
* Must be > 0.
*/
public void minAllocationChunk(int minAllocationChunk) {
if (minAllocationChunk <= 0) {
throw new IllegalArgumentException("minAllocationChunk must be > 0");
}
this.minAllocationChunk = minAllocationChunk;
}
@Override
public void updateStreamableBytes(StreamState streamState) {
state(streamState.stream()).updateStreamableBytes(streamableBytes(streamState),
streamState.hasFrame(),
streamState.windowSize());
}
@Override
public void updateDependencyTree(int childStreamId, int parentStreamId, short weight, boolean exclusive) {
// This class ignores priority and dependency!
}
@Override
public boolean distribute(int maxBytes, Writer writer) throws Http2Exception {
final int size = queue.size();
if (size == 0) {
return totalStreamableBytes > 0;
}
final int chunkSize = max(minAllocationChunk, maxBytes / size);
State state = queue.pollFirst();
do {
state.enqueued = false;
if (state.windowNegative) {
continue;
}
if (maxBytes == 0 && state.streamableBytes > 0) {
// Stop at the first state that can't send. Add this state back to the head of the queue. Note
// that empty frames at the head of the queue will always be written, assuming the stream window
// is not negative.
queue.addFirst(state);
state.enqueued = true;
break;
}
// Allocate as much data as we can for this stream.
int chunk = min(chunkSize, min(maxBytes, state.streamableBytes));
maxBytes -= chunk;
// Write the allocated bytes and enqueue as necessary.
state.write(chunk, writer);
} while ((state = queue.pollFirst()) != null);
return totalStreamableBytes > 0;
}
private State state(Http2Stream stream) {
return checkNotNull(stream, "stream").getProperty(stateKey);
}
/**
* For testing only!
*/
int streamableBytes0(Http2Stream stream) {
return state(stream).streamableBytes;
}
/**
* The remote flow control state for a single stream.
*/
private final class State {
final Http2Stream stream;
int streamableBytes;
boolean windowNegative;
boolean enqueued;
boolean writing;
State(Http2Stream stream) {
this.stream = stream;
}
void updateStreamableBytes(int newStreamableBytes, boolean hasFrame, int windowSize) {
assert hasFrame || newStreamableBytes == 0 :
"hasFrame: " + hasFrame + " newStreamableBytes: " + newStreamableBytes;
int delta = newStreamableBytes - streamableBytes;
if (delta != 0) {
streamableBytes = newStreamableBytes;
totalStreamableBytes += delta;
}
// In addition to only enqueuing state when they have frames we enforce the following restrictions:
// 1. If the window has gone negative. We never want to queue a state. However we also don't want to
// Immediately remove the item if it is already queued because removal from deque is O(n). So
// we allow it to stay queued and rely on the distribution loop to remove this state.
// 2. If the window is zero we only want to queue if we are not writing. If we are writing that means
// we gave the state a chance to write zero length frames. We wait until updateStreamableBytes is
// called again before this state is allowed to write.
windowNegative = windowSize < 0;
if (hasFrame && (windowSize > 0 || (windowSize == 0 && !writing))) {
addToQueue();
}
}
/**
* Write any allocated bytes for the given stream and updates the streamable bytes,
* assuming all of the bytes will be written.
*/
void write(int numBytes, Writer writer) throws Http2Exception {
writing = true;
try {
// Write the allocated bytes.
writer.write(stream, numBytes);
} catch (Throwable t) {
throw connectionError(INTERNAL_ERROR, t, "byte distribution write error");
} finally {
writing = false;
}
}
void addToQueue() {
if (!enqueued) {
enqueued = true;
queue.addLast(this);
}
}
void removeFromQueue() {
if (enqueued) {
enqueued = false;
queue.remove(this);
}
}
void close() {
// Remove this state from the queue.
removeFromQueue();
// Clear the streamable bytes.
updateStreamableBytes(0, false, 0);
}
}
}