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Qetcher Java client, OSGi bundle, minimal dependencies
//
// ========================================================================
// Copyright (c) 1995-2018 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.http2;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;
import org.eclipse.jetty.http2.frames.Frame;
import org.eclipse.jetty.http2.frames.WindowUpdateFrame;
import org.eclipse.jetty.util.Atomics;
import org.eclipse.jetty.util.Callback;
import org.eclipse.jetty.util.annotation.ManagedAttribute;
import org.eclipse.jetty.util.annotation.ManagedObject;
/**
* A flow control strategy that accumulates updates and emits window control
* frames when the accumulated value reaches a threshold.
* The sender flow control window is represented in the receiver as two
* buckets: a bigger bucket, initially full, that is drained when data is
* received, and a smaller bucket, initially empty, that is filled when data is
* consumed. Only the smaller bucket can refill the bigger bucket.
* The smaller bucket is defined as a fraction of the bigger bucket.
* For a more visual representation, see the
* rocking bamboo fountain.
* The algorithm works in this way.
* The initial bigger bucket (BB) capacity is 100, and let's imagine the smaller
* bucket (SB) being 40% of the bigger bucket: 40.
* The receiver receives a data frame of 60, so now BB=40; the data frame is
* passed to the application that consumes 25, so now SB=25. Since SB is not full,
* no window control frames are emitted.
* The application consumes other 20, so now SB=45. Since SB is full, its 45
* are transferred to BB, which is now BB=85, and a window control frame is sent
* with delta=45.
* The application consumes the remaining 15, so now SB=15, and no window
* control frame is emitted.
*/
@ManagedObject
public class BufferingFlowControlStrategy extends AbstractFlowControlStrategy
{
private final AtomicInteger maxSessionRecvWindow = new AtomicInteger(DEFAULT_WINDOW_SIZE);
private final AtomicInteger sessionLevel = new AtomicInteger();
private final Map streamLevels = new ConcurrentHashMap<>();
private float bufferRatio;
public BufferingFlowControlStrategy(float bufferRatio)
{
this(DEFAULT_WINDOW_SIZE, bufferRatio);
}
public BufferingFlowControlStrategy(int initialStreamSendWindow, float bufferRatio)
{
super(initialStreamSendWindow);
this.bufferRatio = bufferRatio;
}
@ManagedAttribute("The ratio between the receive buffer and the consume buffer")
public float getBufferRatio()
{
return bufferRatio;
}
public void setBufferRatio(float bufferRatio)
{
this.bufferRatio = bufferRatio;
}
@Override
public void onStreamCreated(IStream stream)
{
super.onStreamCreated(stream);
streamLevels.put(stream, new AtomicInteger());
}
@Override
public void onStreamDestroyed(IStream stream)
{
streamLevels.remove(stream);
super.onStreamDestroyed(stream);
}
@Override
public void onDataConsumed(ISession session, IStream stream, int length)
{
if (length <= 0)
return;
float ratio = bufferRatio;
int level = sessionLevel.addAndGet(length);
int maxLevel = (int)(maxSessionRecvWindow.get() * ratio);
if (level > maxLevel)
{
if (sessionLevel.compareAndSet(level, 0))
{
session.updateRecvWindow(level);
if (LOG.isDebugEnabled())
LOG.debug("Data consumed, {} bytes, updated session recv window by {}/{} for {}", length, level, maxLevel, session);
session.frames(null, Callback.NOOP, new WindowUpdateFrame(0, level), Frame.EMPTY_ARRAY);
}
else
{
if (LOG.isDebugEnabled())
LOG.debug("Data consumed, {} bytes, concurrent session recv window level {}/{} for {}", length, sessionLevel, maxLevel, session);
}
}
else
{
if (LOG.isDebugEnabled())
LOG.debug("Data consumed, {} bytes, session recv window level {}/{} for {}", length, level, maxLevel, session);
}
if (stream != null)
{
if (stream.isRemotelyClosed())
{
if (LOG.isDebugEnabled())
LOG.debug("Data consumed, {} bytes, ignoring update stream recv window for remotely closed {}", length, stream);
}
else
{
AtomicInteger streamLevel = streamLevels.get(stream);
if (streamLevel != null)
{
level = streamLevel.addAndGet(length);
maxLevel = (int)(getInitialStreamRecvWindow() * ratio);
if (level > maxLevel)
{
level = streamLevel.getAndSet(0);
stream.updateRecvWindow(level);
if (LOG.isDebugEnabled())
LOG.debug("Data consumed, {} bytes, updated stream recv window by {}/{} for {}", length, level, maxLevel, stream);
session.frames(stream, Callback.NOOP, new WindowUpdateFrame(stream.getId(), level), Frame.EMPTY_ARRAY);
}
else
{
if (LOG.isDebugEnabled())
LOG.debug("Data consumed, {} bytes, stream recv window level {}/{} for {}", length, level, maxLevel, stream);
}
}
}
}
}
@Override
public void windowUpdate(ISession session, IStream stream, WindowUpdateFrame frame)
{
super.windowUpdate(session, stream, frame);
// Window updates cannot be negative.
// The SettingsFrame.INITIAL_WINDOW_SIZE setting
// only influences the *stream* window size.
// Therefore the session window can only be enlarged,
// and here we keep track of its max value.
// Updating the max session recv window is done here
// so that if a peer decides to send an unilateral
// window update to enlarge the session window,
// without the corresponding data consumption, here
// we can track it.
// Note that it is not perfect, since there is a time
// window between the session recv window being updated
// before the window update frame is sent, and the
// invocation of this method: in between data may arrive
// and reduce the session recv window size.
// But eventually the max value will be seen.
// Note that we cannot avoid the time window described
// above by updating the session recv window from here
// because there is a race between the sender and the
// receiver: the sender may receive a window update and
// send more data, while this method has not yet been
// invoked; when the data is received the session recv
// window may become negative and the connection will
// be closed (per specification).
if (frame.getStreamId() == 0)
{
int sessionWindow = session.updateRecvWindow(0);
Atomics.updateMax(maxSessionRecvWindow, sessionWindow);
}
}
@Override
public String toString()
{
return String.format("%s@%x[ratio=%.2f,sessionLevel=%s,sessionStallTime=%dms,streamsStallTime=%dms]",
getClass().getSimpleName(),
hashCode(),
bufferRatio,
sessionLevel,
getSessionStallTime(),
getStreamsStallTime());
}
}
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