| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF 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 org.apache.giraph.utils; |
| |
| import java.util.concurrent.Semaphore; |
| |
| import static com.google.common.base.Preconditions.checkState; |
| |
| /** |
| * Implementation of a semaphore where number of available permits can change |
| */ |
| public final class AdjustableSemaphore extends Semaphore { |
| /** Maximum number of available permits */ |
| private int maxPermits; |
| |
| /** |
| * Constructor |
| * @param permits initial number of available permits |
| */ |
| public AdjustableSemaphore(int permits) { |
| super(permits); |
| maxPermits = permits; |
| } |
| |
| @edu.umd.cs.findbugs.annotations.SuppressWarnings( |
| "UG_SYNC_SET_UNSYNC_GET") |
| public int getMaxPermits() { |
| return maxPermits; |
| } |
| |
| /** |
| * Adjusts the maximum number of available permits. |
| * |
| * @param newMax max number of permits |
| */ |
| public synchronized void setMaxPermits(int newMax) { |
| checkState(newMax >= 0, "setMaxPermits: number of permits cannot be " + |
| "less than 0"); |
| int delta = newMax - this.maxPermits; |
| if (delta > 0) { |
| // Releasing semaphore to make room for 'delta' more permits |
| release(delta); |
| } else if (delta < 0) { |
| // Reducing number of permits in the semaphore |
| reducePermits(-delta); |
| } |
| this.maxPermits = newMax; |
| } |
| } |