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/*
* Copyright 2014-2025 Real Logic Limited.
*
* 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
*
* https://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.aeron.driver;
import java.net.InetSocketAddress;
/**
* Strategy for applying congestion control to determine the receiver window length of the Status Messages.
*/
public interface CongestionControl extends AutoCloseable
{
/**
* Bit flag for if a status message should be forced out.
*/
int FORCE_STATUS_MESSAGE_BIT = 0x1;
/**
* Pack values into a long, so they can be returned on the stack without allocation.
*
* @param receiverWindowLength to go in the lower bits.
* @param forceStatusMessage to go in the higher bits.
* @return the packed value.
*/
static long packOutcome(final int receiverWindowLength, final boolean forceStatusMessage)
{
final int flags = forceStatusMessage ? FORCE_STATUS_MESSAGE_BIT : 0x0;
return ((long)flags << 32) | receiverWindowLength;
}
/**
* Extract the receiver window length from the packed value.
*
* @param outcome as the packed value.
* @return the receiver window length.
*/
static int receiverWindowLength(final long outcome)
{
return (int)(outcome & 0xFFFFFFFFL);
}
/**
* Extract the boolean value for if a status message should be forced from the packed value.
*
* @param outcome which is packed containing the force status message flag.
* @return true if the force status message bit has been set.
*/
static boolean shouldForceStatusMessage(final long outcome)
{
return ((int)(outcome >>> 32) & FORCE_STATUS_MESSAGE_BIT) == FORCE_STATUS_MESSAGE_BIT;
}
/**
* Threshold increment in a window after which a status message should be scheduled.
*
* @param windowLength to calculate the threshold from.
* @return the threshold in the window after which a status message should be scheduled.
*/
static int threshold(final int windowLength)
{
return windowLength >> 2;
}
/**
* Polled by {@link Receiver} to determine when to initiate an RTT measurement to a Sender.
*
* @param nowNs in nanoseconds
* @return true for should measure RTT now or false for no measurement
*/
boolean shouldMeasureRtt(long nowNs);
/**
* Called by {@link Receiver} to record that a measurement request has been sent.
*
* @param nowNs in nanoseconds.
*/
void onRttMeasurementSent(long nowNs);
/**
* Called by {@link Receiver} on reception of an RTT Measurement.
*
* @param nowNs in nanoseconds
* @param rttNs to the Sender in nanoseconds
* @param srcAddress of the Sender
*/
void onRttMeasurement(long nowNs, long rttNs, InetSocketAddress srcAddress);
/**
* Called by {@link DriverConductor} upon execution of {@link PublicationImage#trackRebuild(long)} to
* pass on current status.
*
* The return value must be packed using {@link CongestionControl#packOutcome(int, boolean)}.
*
* @param nowNs current time
* @param newConsumptionPosition of the subscribers
* @param lastSmPosition of the image
* @param hwmPosition of the image
* @param startingRebuildPosition of the rebuild
* @param endingRebuildPosition of the rebuild
* @param lossOccurred during rebuild
* @return outcome of congestion control calculation containing window length and whether to force sending an SM.
*/
long onTrackRebuild(
long nowNs,
long newConsumptionPosition,
long lastSmPosition,
long hwmPosition,
long startingRebuildPosition,
long endingRebuildPosition,
boolean lossOccurred);
/**
* Called by {@link DriverConductor} to initialise window length for a new {@link PublicationImage}.
*
* @return initial window length for flow and congestion control.
*/
int initialWindowLength();
/**
* Called by {@link DriverConductor} limit the window length for a new {@link PublicationImage}.
*
* @return maximum window length for flow and congestion control.
*/
int maxWindowLength();
/**
* {@inheritDoc}
*/
void close();
}