LinearBackoffManager.java
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package org.apache.hc.client5.http.impl.classic;
import org.apache.hc.client5.http.HttpRoute;
import org.apache.hc.client5.http.classic.BackoffManager;
import org.apache.hc.core5.annotation.Contract;
import org.apache.hc.core5.annotation.ThreadingBehavior;
import org.apache.hc.core5.pool.ConnPoolControl;
import org.apache.hc.core5.util.Args;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;
/**
* An implementation of {@link BackoffManager} that uses a linear backoff strategy to adjust the maximum number
* of connections per route in an {@link org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager}.
* This class is designed to be thread-safe and can be used in multi-threaded environments.
* <p>
* The linear backoff strategy increases or decreases the maximum number of connections per route by a fixed increment
* when backing off or probing, respectively. The adjustments are made based on a cool-down period, during which no
* further adjustments will be made.
* <p>
* The {@code LinearBackoffManager} is intended to be used with a {@link org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager},
* which provides the {@link ConnPoolControl} interface. This class interacts with the {@code PoolingHttpClientConnectionManager}
* to adjust the maximum number of connections per route.
* <p>
* Example usage:
* <pre>
* PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();
* LinearBackoffManager backoffManager = new LinearBackoffManager(connectionManager, 1);
* // Use the backoffManager with the connectionManager in your application
* </pre>
*
* @see BackoffManager
* @see ConnPoolControl
* @see org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManager
* @since 5.3
*/
@Contract(threading = ThreadingBehavior.SAFE)
public class LinearBackoffManager extends AbstractBackoff {
private static final Logger LOG = LoggerFactory.getLogger(LinearBackoffManager.class);
/**
* The backoff increment used when adjusting connection pool sizes.
* The pool size will be increased or decreased by this value during the backoff process.
* The increment must be positive.
*/
private final int increment;
private final ConcurrentHashMap<HttpRoute, AtomicInteger> routeAttempts;
/**
* Constructs a new LinearBackoffManager with the specified connection pool control.
* The backoff increment is set to {@code 1} by default.
*
* @param connPoolControl the connection pool control to be used by this LinearBackoffManager
*/
public LinearBackoffManager(final ConnPoolControl<HttpRoute> connPoolControl) {
this(connPoolControl, 1);
}
/**
* Constructs a new LinearBackoffManager with the specified connection pool control and backoff increment.
*
* @param connPoolControl the connection pool control to be used by this LinearBackoffManager
* @param increment the backoff increment to be used when adjusting connection pool sizes
* @throws IllegalArgumentException if connPoolControl is {@code null} or increment is not positive
*/
public LinearBackoffManager(final ConnPoolControl<HttpRoute> connPoolControl, final int increment) {
super(connPoolControl);
this.increment = Args.positive(increment, "Increment");
routeAttempts = new ConcurrentHashMap<>();
}
@Override
public void backOff(final HttpRoute route) {
final Instant now = Instant.now();
if (shouldSkip(route, now)) {
if (LOG.isDebugEnabled()) {
LOG.debug("BackOff not applied for route: {}, cool-down period not elapsed", route);
}
return;
}
final AtomicInteger attempt = routeAttempts.compute(route, (r, oldValue) -> {
if (oldValue == null) {
return new AtomicInteger(1);
}
oldValue.incrementAndGet();
return oldValue;
});
getLastRouteBackoffs().put(route, now);
final int currentMax = getConnPerRoute().getMaxPerRoute(route);
getConnPerRoute().setMaxPerRoute(route, getBackedOffPoolSize(currentMax));
attempt.incrementAndGet();
if (LOG.isDebugEnabled()) {
LOG.debug("Backoff applied for route: {}, new max connections: {}", route, getConnPerRoute().getMaxPerRoute(route));
}
}
/**
* Adjusts the maximum number of connections for the specified route, decreasing it by the increment value.
* The method ensures that adjustments only happen after the cool-down period has passed since the last adjustment.
*
* @param route the HttpRoute for which the maximum number of connections will be decreased
*/
@Override
public void probe(final HttpRoute route) {
final Instant now = Instant.now();
if (shouldSkip(route, now)) {
if (LOG.isDebugEnabled()) {
LOG.debug("Probe not applied for route: {}, cool-down period not elapsed", route);
}
return;
}
routeAttempts.compute(route, (r, oldValue) -> {
if (oldValue == null || oldValue.get() <= 1) {
return null;
}
oldValue.decrementAndGet();
return oldValue;
});
getLastRouteProbes().put(route, now);
final int currentMax = getConnPerRoute().getMaxPerRoute(route);
final int newMax = Math.max(currentMax - increment, getCap().get()); // Ensure the new max does not go below the cap
getConnPerRoute().setMaxPerRoute(route, newMax);
if (LOG.isDebugEnabled()) {
LOG.debug("Probe applied for route: {}, new max connections: {}", route, getConnPerRoute().getMaxPerRoute(route));
}
}
/**
* Determines whether an adjustment action (backoff or probe) should be skipped for the given HttpRoute based on the cool-down period.
* If the time elapsed since the last successful probe or backoff for the given route is less than the cool-down
* period, the method returns true. Otherwise, it returns false.
* <p>
* This method is used by both backOff() and probe() methods to enforce the cool-down period before making adjustments
* to the connection pool size.
*
* @param route the {@link HttpRoute} to check
* @param now the current {@link Instant} used to calculate the time since the last probe or backoff
* @return true if the cool-down period has not elapsed since the last probe or backoff, false otherwise
*/
private boolean shouldSkip(final HttpRoute route, final Instant now) {
final Instant lastProbe = getLastRouteProbes().getOrDefault(route, Instant.EPOCH);
final Instant lastBackoff = getLastRouteBackoffs().getOrDefault(route, Instant.EPOCH);
return Duration.between(lastProbe, now).compareTo(getCoolDown().get().toDuration()) < 0 ||
Duration.between(lastBackoff, now).compareTo(getCoolDown().get().toDuration()) < 0;
}
/**
* Returns the new pool size after applying the linear backoff algorithm.
* The new pool size is calculated by adding the increment value to the current pool size.
*
* @param curr the current pool size
* @return the new pool size after applying the linear backoff
*/
@Override
protected int getBackedOffPoolSize(final int curr) {
return curr + increment;
}
/**
* This method is not used in LinearBackoffManager's implementation.
* It is provided to fulfill the interface requirement and for potential future extensions or modifications
* of LinearBackoffManager that may use the backoff factor.
*
* @param d the backoff factor, not used in the current implementation
*/
@Override
public void setBackoffFactor(final double d) {
// Intentionally empty, as the backoff factor is not used in LinearBackoffManager
}
}