ResourceManager.java

/*
 * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package sun.net;

import java.net.SocketException;
import java.util.concurrent.atomic.AtomicInteger;
import sun.security.action.GetPropertyAction;

/**
 * Manages count of total number of UDP sockets and ensures that exception is thrown if we try to create more than the configured limit.
 *
 * This functionality could be put in NetHooks some time in future.
 */
/*
 * UDP Socket进行创建和关闭操作之前的回调。
 * 当存在安全管理器时，限制每个虚拟机上允许打开的最大UDP连接数量。
 */
public class ResourceManager {
    
    /**
     * default maximum number of udp sockets per VM when a security manager is enabled.
     * The default is 25 which is high enough to be useful but low enough to be well below the maximum number of port numbers actually available on all OSes
     * when multiplied by the maximum feasible number of VM processes that could practically be spawned.
     */
    
    private static final int DEFAULT_MAX_SOCKETS = 25;
    
    private static final int maxSockets;
    
    private static final AtomicInteger numSockets;
    
    static {
        String prop = GetPropertyAction.privilegedGetProperty("sun.net.maxDatagramSockets");
        
        int defmax = DEFAULT_MAX_SOCKETS;
        try {
            if(prop != null) {
                defmax = Integer.parseInt(prop);
            }
        } catch(NumberFormatException e) {
        }
        maxSockets = defmax;
        numSockets = new AtomicInteger(0);
    }
    
    // 创建UDP-Socket之时的回调
    public static void beforeUdpCreate() throws SocketException {
        if(System.getSecurityManager() != null) {
            if(numSockets.incrementAndGet()>maxSockets) {
                numSockets.decrementAndGet();
                throw new SocketException("maximum number of DatagramSockets reached");
            }
        }
    }
    
    // 关闭UDP-Socket之时的回调
    public static void afterUdpClose() {
        if(System.getSecurityManager() != null) {
            numSockets.decrementAndGet();
        }
    }
    
}