/*
* Copyright 2015 Netflix, Inc.
*
* 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
*
* 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.reactivex.netty.client.pool;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
/**
* An implementation of {@link PoolLimitDeterminationStrategy} that limits the pool based on a maximum connections limit.
* This limit can be increased or decreased at runtime.
*/
public class MaxConnectionsBasedStrategy implements PoolLimitDeterminationStrategy {
public static final int DEFAULT_MAX_CONNECTIONS = 1000;
private final AtomicInteger limitEnforcer;
private final AtomicInteger maxConnections;
public MaxConnectionsBasedStrategy() {
this(DEFAULT_MAX_CONNECTIONS);
}
public MaxConnectionsBasedStrategy(int maxConnections) {
this.maxConnections = new AtomicInteger(maxConnections);
limitEnforcer = new AtomicInteger();
}
@Override
public boolean acquireCreationPermit(long acquireStartTime, TimeUnit timeUnit) {
/**
* As opposed to limitEnforcer.incrementAndGet() we follow this model as this does not change the limitEnforcer
* value unless there are enough permits.
* If we were to use incrementAndGet(), in case of overflow (from max allowed limit) we would have to decrement
* the limitEnforcer. This may show temporary overflows in getMaxConnections() which may be disturbing for a
* user. However, even if we use incrementAndGet() the counter corrects itself over time.
* This is just a more semantically correct implementation with similar performance characterstics as
* incrementAndGet()
*/
for (;;) {
final int currentValue = limitEnforcer.get();
final int newValue = currentValue + 1;
final int maxAllowedConnections = maxConnections.get();
if (newValue <= maxAllowedConnections) {
if (limitEnforcer.compareAndSet(currentValue, newValue)) {
return true;
}
} else {
return false;
}
}
}
public int incrementMaxConnections(int incrementBy) {
return maxConnections.addAndGet(incrementBy);
}
public int decrementMaxConnections(int decrementBy) {
return maxConnections.addAndGet(-1 * decrementBy);
}
public int getMaxConnections() {
return maxConnections.get();
}
@Override
public int getAvailablePermits() {
return maxConnections.get() - limitEnforcer.get();
}
@Override
public void releasePermit() {
/**
* As opposed to limitEnforcer.decrementAndGet() we follow this model as this does not change the limitEnforcer
* value unless there are enough permits.
* If we were to use decrementAndGet(), in case of overflow (from max allowed limit) we would have to decrement
* the limitEnforcer. This may show temporary overflows in getMaxConnections() which may be disturbing for a
* user. However, even if we use decrementAndGet() the counter corrects itself over time.
* This is just a more semantically correct implementation with similar performance characterstics as
* decrementAndGet()
*/
for (;;) {
final int currentValue = limitEnforcer.get();
final int newValue = currentValue - 1;
if (newValue >= 0) {
if (!limitEnforcer.compareAndSet(currentValue, newValue)) {
continue;
}
}
break;
}
}
}