/*
* Copyright 2014 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.channel.ChannelHandlerContext;
import io.netty.handler.codec.http2.StreamByteDistributor.Writer;
import io.netty.util.BooleanSupplier;
import io.netty.util.internal.UnstableApi;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
import java.util.ArrayDeque;
import java.util.Deque;
import static io.netty.handler.codec.http2.Http2CodecUtil.DEFAULT_WINDOW_SIZE;
import static io.netty.handler.codec.http2.Http2CodecUtil.MAX_WEIGHT;
import static io.netty.handler.codec.http2.Http2CodecUtil.MIN_WEIGHT;
import static io.netty.handler.codec.http2.Http2Error.FLOW_CONTROL_ERROR;
import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
import static io.netty.handler.codec.http2.Http2Exception.streamError;
import static io.netty.handler.codec.http2.Http2Stream.State.HALF_CLOSED_LOCAL;
import static io.netty.util.internal.ObjectUtil.checkNotNull;
import static java.lang.Math.max;
import static java.lang.Math.min;
/**
* Basic implementation of {@link Http2RemoteFlowController}.
* <p>
* This class is <strong>NOT</strong> thread safe. The assumption is all methods must be invoked from a single thread.
* Typically this thread is the event loop thread for the {@link ChannelHandlerContext} managed by this class.
*/
@UnstableApi
public class DefaultHttp2RemoteFlowController implements Http2RemoteFlowController {
private static final InternalLogger logger =
InternalLoggerFactory.getInstance(DefaultHttp2RemoteFlowController.class);
private static final int MIN_WRITABLE_CHUNK = 32 * 1024;
private final Http2Connection connection;
private final Http2Connection.PropertyKey stateKey;
private final StreamByteDistributor streamByteDistributor;
private final FlowState connectionState;
private int initialWindowSize = DEFAULT_WINDOW_SIZE;
private WritabilityMonitor monitor;
private ChannelHandlerContext ctx;
public DefaultHttp2RemoteFlowController(Http2Connection connection) {
this(connection, (Listener) null);
}
public DefaultHttp2RemoteFlowController(Http2Connection connection,
StreamByteDistributor streamByteDistributor) {
this(connection, streamByteDistributor, null);
}
public DefaultHttp2RemoteFlowController(Http2Connection connection, final Listener listener) {
this(connection, new WeightedFairQueueByteDistributor(connection), listener);
}
public DefaultHttp2RemoteFlowController(Http2Connection connection,
StreamByteDistributor streamByteDistributor,
final Listener listener) {
this.connection = checkNotNull(connection, "connection");
this.streamByteDistributor = checkNotNull(streamByteDistributor, "streamWriteDistributor");
// Add a flow state for the connection.
stateKey = connection.newKey();
connectionState = new FlowState(connection.connectionStream());
connection.connectionStream().setProperty(stateKey, connectionState);
// Monitor may depend upon connectionState, and so initialize after connectionState
listener(listener);
monitor.windowSize(connectionState, initialWindowSize);
// Register for notification of new streams.
connection.addListener(new Http2ConnectionAdapter() {
@Override
public void onStreamAdded(Http2Stream stream) {
// If the stream state is not open then the stream is not yet eligible for flow controlled frames and
// only requires the ReducedFlowState. Otherwise the full amount of memory is required.
stream.setProperty(stateKey, new FlowState(stream));
}
@Override
public void onStreamActive(Http2Stream stream) {
// If the object was previously created, but later activated then we have to ensure the proper
// initialWindowSize is used.
monitor.windowSize(state(stream), initialWindowSize);
}
@Override
public void onStreamClosed(Http2Stream stream) {
// Any pending frames can never be written, cancel and
// write errors for any pending frames.
state(stream).cancel();
}
@Override
public void onStreamHalfClosed(Http2Stream stream) {
if (HALF_CLOSED_LOCAL.equals(stream.state())) {
/**
* When this method is called there should not be any
* pending frames left if the API is used correctly. However,
* it is possible that a erroneous application can sneak
* in a frame even after having already written a frame with the
* END_STREAM flag set, as the stream state might not transition
* immediately to HALF_CLOSED_LOCAL / CLOSED due to flow control
* delaying the write.
*
* This is to cancel any such illegal writes.
*/
state(stream).cancel();
}
}
});
}
/**
* {@inheritDoc}
* <p>
* Any queued {@link FlowControlled} objects will be sent.
*/
@Override
public void channelHandlerContext(ChannelHandlerContext ctx) throws Http2Exception {
this.ctx = checkNotNull(ctx, "ctx");
// Writing the pending bytes will not check writability change and instead a writability change notification
// to be provided by an explicit call.
channelWritabilityChanged();
// Don't worry about cleaning up queued frames here if ctx is null. It is expected that all streams will be
// closed and the queue cleanup will occur when the stream state transitions occur.
// If any frames have been queued up, we should send them now that we have a channel context.
if (isChannelWritable()) {
writePendingBytes();
}
}
@Override
public ChannelHandlerContext channelHandlerContext() {
return ctx;
}
@Override
public void initialWindowSize(int newWindowSize) throws Http2Exception {
assert ctx == null || ctx.executor().inEventLoop();
monitor.initialWindowSize(newWindowSize);
}
@Override
public int initialWindowSize() {
return initialWindowSize;
}
@Override
public int windowSize(Http2Stream stream) {
return state(stream).windowSize();
}
@Override
public boolean isWritable(Http2Stream stream) {
return monitor.isWritable(state(stream));
}
@Override
public void channelWritabilityChanged() throws Http2Exception {
monitor.channelWritabilityChange();
}
@Override
public void updateDependencyTree(int childStreamId, int parentStreamId, short weight, boolean exclusive) {
// It is assumed there are all validated at a higher level. For example in the Http2FrameReader.
assert weight >= MIN_WEIGHT && weight <= MAX_WEIGHT : "Invalid weight";
assert childStreamId != parentStreamId : "A stream cannot depend on itself";
assert childStreamId > 0 && parentStreamId >= 0 : "childStreamId must be > 0. parentStreamId must be >= 0.";
streamByteDistributor.updateDependencyTree(childStreamId, parentStreamId, weight, exclusive);
}
private boolean isChannelWritable() {
return ctx != null && isChannelWritable0();
}
private boolean isChannelWritable0() {
return ctx.channel().isWritable();
}
@Override
public void listener(Listener listener) {
monitor = listener == null ? new WritabilityMonitor() : new ListenerWritabilityMonitor(listener);
}
@Override
public void incrementWindowSize(Http2Stream stream, int delta) throws Http2Exception {
assert ctx == null || ctx.executor().inEventLoop();
monitor.incrementWindowSize(state(stream), delta);
}
@Override
public void addFlowControlled(Http2Stream stream, FlowControlled frame) {
// The context can be null assuming the frame will be queued and send later when the context is set.
assert ctx == null || ctx.executor().inEventLoop();
checkNotNull(frame, "frame");
try {
monitor.enqueueFrame(state(stream), frame);
} catch (Throwable t) {
frame.error(ctx, t);
}
}
@Override
public boolean hasFlowControlled(Http2Stream stream) {
return state(stream).hasFrame();
}
private FlowState state(Http2Stream stream) {
return (FlowState) stream.getProperty(stateKey);
}
/**
* Returns the flow control window for the entire connection.
*/
private int connectionWindowSize() {
return connectionState.windowSize();
}
private int minUsableChannelBytes() {
// The current allocation algorithm values "fairness" and doesn't give any consideration to "goodput". It
// is possible that 1 byte will be allocated to many streams. In an effort to try to make "goodput"
// reasonable with the current allocation algorithm we have this "cheap" check up front to ensure there is
// an "adequate" amount of connection window before allocation is attempted. This is not foolproof as if the
// number of streams is >= this minimal number then we may still have the issue, but the idea is to narrow the
// circumstances in which this can happen without rewriting the allocation algorithm.
return max(ctx.channel().config().getWriteBufferLowWaterMark(), MIN_WRITABLE_CHUNK);
}
private int maxUsableChannelBytes() {
// If the channel isWritable, allow at least minUsableChannelBytes.
int channelWritableBytes = (int) min(Integer.MAX_VALUE, ctx.channel().bytesBeforeUnwritable());
int usableBytes = channelWritableBytes > 0 ? max(channelWritableBytes, minUsableChannelBytes()) : 0;
// Clip the usable bytes by the connection window.
return min(connectionState.windowSize(), usableBytes);
}
/**
* The amount of bytes that can be supported by underlying {@link io.netty.channel.Channel} without
* queuing "too-much".
*/
private int writableBytes() {
return min(connectionWindowSize(), maxUsableChannelBytes());
}
@Override
public void writePendingBytes() throws Http2Exception {
monitor.writePendingBytes();
}
/**
* The remote flow control state for a single stream.
*/
private final class FlowState implements StreamByteDistributor.StreamState {
private final Http2Stream stream;
private final Deque<FlowControlled> pendingWriteQueue;
private int window;
private int pendingBytes;
private boolean markedWritable;
/**
* Set to true while a frame is being written, false otherwise.
*/
private boolean writing;
/**
* Set to true if cancel() was called.
*/
private boolean cancelled;
private BooleanSupplier isWritableSupplier = new BooleanSupplier() {
@Override
public boolean get() throws Exception {
return windowSize() > pendingBytes();
}
};
FlowState(Http2Stream stream) {
this.stream = stream;
pendingWriteQueue = new ArrayDeque<FlowControlled>(2);
}
/**
* Determine if the stream associated with this object is writable.
* @return {@code true} if the stream associated with this object is writable.
*/
boolean isWritable() {
try {
return isWritableSupplier.get();
} catch (Throwable cause) {
throw new Error("isWritableSupplier should never throw!", cause);
}
}
/**
* The stream this state is associated with.
*/
@Override
public Http2Stream stream() {
return stream;
}
/**
* Returns the parameter from the last call to {@link #markedWritability(boolean)}.
*/
boolean markedWritability() {
return markedWritable;
}
/**
* Save the state of writability.
*/
void markedWritability(boolean isWritable) {
this.markedWritable = isWritable;
}
@Override
public int windowSize() {
return window;
}
/**
* Reset the window size for this stream.
*/
void windowSize(int initialWindowSize) {
window = initialWindowSize;
}
/**
* Write the allocated bytes for this stream.
* @return the number of bytes written for a stream or {@code -1} if no write occurred.
*/
int writeAllocatedBytes(int allocated) {
final int initialAllocated = allocated;
int writtenBytes;
// In case an exception is thrown we want to remember it and pass it to cancel(Throwable).
Throwable cause = null;
FlowControlled frame;
try {
assert !writing;
writing = true;
// Write the remainder of frames that we are allowed to
boolean writeOccurred = false;
while (!cancelled && (frame = peek()) != null) {
int maxBytes = min(allocated, writableWindow());
if (maxBytes <= 0 && frame.size() > 0) {
// The frame still has data, but the amount of allocated bytes has been exhausted.
// Don't write needless empty frames.
break;
}
writeOccurred = true;
int initialFrameSize = frame.size();
try {
frame.write(ctx, max(0, maxBytes));
if (frame.size() == 0) {
// This frame has been fully written, remove this frame and notify it.
// Since we remove this frame first, we're guaranteed that its error
// method will not be called when we call cancel.
pendingWriteQueue.remove();
frame.writeComplete();
}
} finally {
// Decrement allocated by how much was actually written.
allocated -= initialFrameSize - frame.size();
}
}
if (!writeOccurred) {
// Either there was no frame, or the amount of allocated bytes has been exhausted.
return -1;
}
} catch (Throwable t) {
// Mark the state as cancelled, we'll clear the pending queue via cancel() below.
cancelled = true;
cause = t;
} finally {
writing = false;
// Make sure we always decrement the flow control windows
// by the bytes written.
writtenBytes = initialAllocated - allocated;
decrementPendingBytes(writtenBytes, false);
decrementFlowControlWindow(writtenBytes);
// If a cancellation occurred while writing, call cancel again to
// clear and error all of the pending writes.
if (cancelled) {
cancel(cause);
}
}
return writtenBytes;
}
/**
* Increments the flow control window for this stream by the given delta and returns the new value.
*/
int incrementStreamWindow(int delta) throws Http2Exception {
if (delta > 0 && Integer.MAX_VALUE - delta < window) {
throw streamError(stream.id(), FLOW_CONTROL_ERROR,
"Window size overflow for stream: %d", stream.id());
}
window += delta;
streamByteDistributor.updateStreamableBytes(this);
return window;
}
/**
* Returns the maximum writable window (minimum of the stream and connection windows).
*/
private int writableWindow() {
return min(window, connectionWindowSize());
}
@Override
public int pendingBytes() {
return pendingBytes;
}
/**
* Adds the {@code frame} to the pending queue and increments the pending byte count.
*/
void enqueueFrame(FlowControlled frame) {
FlowControlled last = pendingWriteQueue.peekLast();
if (last == null) {
enqueueFrameWithoutMerge(frame);
return;
}
int lastSize = last.size();
if (last.merge(ctx, frame)) {
incrementPendingBytes(last.size() - lastSize, true);
return;
}
enqueueFrameWithoutMerge(frame);
}
private void enqueueFrameWithoutMerge(FlowControlled frame) {
pendingWriteQueue.offer(frame);
// This must be called after adding to the queue in order so that hasFrame() is
// updated before updating the stream state.
incrementPendingBytes(frame.size(), true);
}
@Override
public boolean hasFrame() {
return !pendingWriteQueue.isEmpty();
}
/**
* Returns the the head of the pending queue, or {@code null} if empty.
*/
private FlowControlled peek() {
return pendingWriteQueue.peek();
}
/**
* Any operations that may be pending are cleared and the status of these operations is failed.
*/
void cancel() {
cancel(null);
}
/**
* Clears the pending queue and writes errors for each remaining frame.
* @param cause the {@link Throwable} that caused this method to be invoked.
*/
private void cancel(Throwable cause) {
cancelled = true;
// Ensure that the queue can't be modified while we are writing.
if (writing) {
return;
}
for (;;) {
FlowControlled frame = pendingWriteQueue.poll();
if (frame == null) {
break;
}
writeError(frame, streamError(stream.id(), INTERNAL_ERROR, cause,
"Stream closed before write could take place"));
}
streamByteDistributor.updateStreamableBytes(this);
isWritableSupplier = BooleanSupplier.FALSE_SUPPLIER;
monitor.stateCancelled(this);
}
/**
* Increments the number of pending bytes for this node and optionally updates the
* {@link StreamByteDistributor}.
*/
private void incrementPendingBytes(int numBytes, boolean updateStreamableBytes) {
pendingBytes += numBytes;
monitor.incrementPendingBytes(numBytes);
if (updateStreamableBytes) {
streamByteDistributor.updateStreamableBytes(this);
}
}
/**
* If this frame is in the pending queue, decrements the number of pending bytes for the stream.
*/
private void decrementPendingBytes(int bytes, boolean updateStreamableBytes) {
incrementPendingBytes(-bytes, updateStreamableBytes);
}
/**
* Decrement the per stream and connection flow control window by {@code bytes}.
*/
private void decrementFlowControlWindow(int bytes) {
try {
int negativeBytes = -bytes;
connectionState.incrementStreamWindow(negativeBytes);
incrementStreamWindow(negativeBytes);
} catch (Http2Exception e) {
// Should never get here since we're decrementing.
throw new IllegalStateException("Invalid window state when writing frame: " + e.getMessage(), e);
}
}
/**
* Discards this {@link FlowControlled}, writing an error. If this frame is in the pending queue,
* the unwritten bytes are removed from this branch of the priority tree.
*/
private void writeError(FlowControlled frame, Http2Exception cause) {
assert ctx != null;
decrementPendingBytes(frame.size(), true);
frame.error(ctx, cause);
}
}
/**
* Abstract class which provides common functionality for writability monitor implementations.
*/
private class WritabilityMonitor {
private boolean inWritePendingBytes;
private long totalPendingBytes;
private final Writer writer = new StreamByteDistributor.Writer() {
@Override
public void write(Http2Stream stream, int numBytes) {
state(stream).writeAllocatedBytes(numBytes);
}
};
/**
* Called when the writability of the underlying channel changes.
* @throws Http2Exception If a write occurs and an exception happens in the write operation.
*/
void channelWritabilityChange() throws Http2Exception { }
/**
* Called when the state is cancelled.
* @param state the state that was cancelled.
*/
void stateCancelled(FlowState state) { }
/**
* Set the initial window size for {@code state}.
* @param state the state to change the initial window size for.
* @param initialWindowSize the size of the window in bytes.
*/
void windowSize(FlowState state, int initialWindowSize) {
state.windowSize(initialWindowSize);
}
/**
* Increment the window size for a particular stream.
* @param state the state associated with the stream whose window is being incremented.
* @param delta The amount to increment by.
* @throws Http2Exception If this operation overflows the window for {@code state}.
*/
void incrementWindowSize(FlowState state, int delta) throws Http2Exception {
state.incrementStreamWindow(delta);
}
/**
* Add a frame to be sent via flow control.
* @param state The state associated with the stream which the {@code frame} is associated with.
* @param frame the frame to enqueue.
* @throws Http2Exception If a writability error occurs.
*/
void enqueueFrame(FlowState state, FlowControlled frame) throws Http2Exception {
state.enqueueFrame(frame);
}
/**
* Increment the total amount of pending bytes for all streams. When any stream's pending bytes changes
* method should be called.
* @param delta The amount to increment by.
*/
final void incrementPendingBytes(int delta) {
totalPendingBytes += delta;
// Notification of writibilty change should be delayed until the end of the top level event.
// This is to ensure the flow controller is more consistent state before calling external listener methods.
}
/**
* Determine if the stream associated with {@code state} is writable.
* @param state The state which is associated with the stream to test writability for.
* @return {@code true} if {@link FlowState#stream()} is writable. {@code false} otherwise.
*/
final boolean isWritable(FlowState state) {
return isWritableConnection() && state.isWritable();
}
final void writePendingBytes() throws Http2Exception {
// Reentry is not permitted during the byte distribution process. It may lead to undesirable distribution of
// bytes and even infinite loops. We protect against reentry and make sure each call has an opportunity to
// cause a distribution to occur. This may be useful for example if the channel's writability changes from
// Writable -> Not Writable (because we are writing) -> Writable (because the user flushed to make more room
// in the channel outbound buffer).
if (inWritePendingBytes) {
return;
}
inWritePendingBytes = true;
try {
int bytesToWrite = writableBytes();
// Make sure we always write at least once, regardless if we have bytesToWrite or not.
// This ensures that zero-length frames will always be written.
for (;;) {
if (!streamByteDistributor.distribute(bytesToWrite, writer) ||
(bytesToWrite = writableBytes()) <= 0 ||
!isChannelWritable0()) {
break;
}
}
} finally {
inWritePendingBytes = false;
}
}
void initialWindowSize(int newWindowSize) throws Http2Exception {
if (newWindowSize < 0) {
throw new IllegalArgumentException("Invalid initial window size: " + newWindowSize);
}
final int delta = newWindowSize - initialWindowSize;
initialWindowSize = newWindowSize;
connection.forEachActiveStream(new Http2StreamVisitor() {
@Override
public boolean visit(Http2Stream stream) throws Http2Exception {
state(stream).incrementStreamWindow(delta);
return true;
}
});
if (delta > 0 && isChannelWritable()) {
// The window size increased, send any pending frames for all streams.
writePendingBytes();
}
}
final boolean isWritableConnection() {
return connectionState.windowSize() - totalPendingBytes > 0 && isChannelWritable();
}
}
/**
* Writability of a {@code stream} is calculated using the following:
* <pre>
* Connection Window - Total Queued Bytes > 0 &&
* Stream Window - Bytes Queued for Stream > 0 &&
* isChannelWritable()
* </pre>
*/
private final class ListenerWritabilityMonitor extends WritabilityMonitor {
private final Listener listener;
private final Http2StreamVisitor checkStreamWritabilityVisitor = new Http2StreamVisitor() {
@Override
public boolean visit(Http2Stream stream) throws Http2Exception {
FlowState state = state(stream);
if (isWritable(state) != state.markedWritability()) {
notifyWritabilityChanged(state);
}
return true;
}
};
ListenerWritabilityMonitor(Listener listener) {
this.listener = listener;
}
@Override
void windowSize(FlowState state, int initialWindowSize) {
super.windowSize(state, initialWindowSize);
try {
checkStateWritability(state);
} catch (Http2Exception e) {
throw new RuntimeException("Caught unexpected exception from window", e);
}
}
@Override
void incrementWindowSize(FlowState state, int delta) throws Http2Exception {
super.incrementWindowSize(state, delta);
checkStateWritability(state);
}
@Override
void initialWindowSize(int newWindowSize) throws Http2Exception {
super.initialWindowSize(newWindowSize);
if (isWritableConnection()) {
// If the write operation does not occur we still need to check all streams because they
// may have transitioned from writable to not writable.
checkAllWritabilityChanged();
}
}
@Override
void enqueueFrame(FlowState state, FlowControlled frame) throws Http2Exception {
super.enqueueFrame(state, frame);
checkConnectionThenStreamWritabilityChanged(state);
}
@Override
void stateCancelled(FlowState state) {
try {
checkConnectionThenStreamWritabilityChanged(state);
} catch (Http2Exception e) {
throw new RuntimeException("Caught unexpected exception from checkAllWritabilityChanged", e);
}
}
@Override
void channelWritabilityChange() throws Http2Exception {
if (connectionState.markedWritability() != isChannelWritable()) {
checkAllWritabilityChanged();
}
}
private void checkStateWritability(FlowState state) throws Http2Exception {
if (isWritable(state) != state.markedWritability()) {
if (state == connectionState) {
checkAllWritabilityChanged();
} else {
notifyWritabilityChanged(state);
}
}
}
private void notifyWritabilityChanged(FlowState state) {
state.markedWritability(!state.markedWritability());
try {
listener.writabilityChanged(state.stream);
} catch (Throwable cause) {
logger.error("Caught Throwable from listener.writabilityChanged", cause);
}
}
private void checkConnectionThenStreamWritabilityChanged(FlowState state) throws Http2Exception {
// It is possible that the connection window and/or the individual stream writability could change.
if (isWritableConnection() != connectionState.markedWritability()) {
checkAllWritabilityChanged();
} else if (isWritable(state) != state.markedWritability()) {
notifyWritabilityChanged(state);
}
}
private void checkAllWritabilityChanged() throws Http2Exception {
// Make sure we mark that we have notified as a result of this change.
connectionState.markedWritability(isWritableConnection());
connection.forEachActiveStream(checkStreamWritabilityVisitor);
}
}
}