Java 线程：内存泄漏

Question

我用 Java 实现了简单的服务器-客户端聊天。这里是服务器的来源：

public class Server {
    final private static int PORT = 50000;

    private static class Read extends Thread {
        private static Socket socket;
        private static String address;

        public Read(Socket socket) {
            this.socket = socket;
            address = socket.getInetAddress().toString().substring(1);
        }

        public void run() {
            try {

                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                String msg;

                while (true) {
                    msg = in.readLine();
                    if (msg == null) {
                        in.close();
                        return;
                    }

                    System.out.println(address + ": " + msg);
                }

            } catch (IOException e) {
                e.printStackTrace();
            }

        }
    }

    private static class Write extends Thread {
        private static Socket socket;

        public Write(Socket socket) {
            this.socket = socket;
        }

        public void run() {
            try {

                PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
                BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
                String msg;

                while (true) {
                    if (socket.isClosed()) {
                        out.close();
                        return;
                    }
                    if (stdin.ready()) {
                        msg = stdin.readLine();
                        out.println(msg);
                    }
                }

            } catch (IOException e) {
                e.printStackTrace();
            }

        }
    }

    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket;
        boolean listening = true;

        serverSocket = new ServerSocket(PORT);

        while (listening) {
            Socket socket = serverSocket.accept();
            String address = socket.getInetAddress().toString().substring(1);
            System.out.println("Connection Established " + address);

            Thread read = new Read(socket);     
            Thread write = new Write(socket);

            read.start();
            write.start();

            try {
                read.join();
                write.join();
            } catch(InterruptedException e) {

            }   

            socket.close();
            System.out.println("Connection Closed " + address);
        }
        serverSocket.close();
    }
}

它工作正常，但有一个问题。对于每个已建立的连接，内存都会不断增长。我认为问题是为线程分配的内存之后没有释放，但我不太确定。我该如何解决？

编辑：客户端程序：

class Client {
    final private static int PORT = 50000;

    private static class Read extends Thread {
        private Socket socket;
        private String address;

        public Read(Socket socket) {
            this.socket = socket;
            address = socket.getInetAddress().toString().substring(1);
        }

        public void run() {
            try {

                BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                String msg;

                while (true) {
                    msg = in.readLine();
                    if (msg == null) {
                        System.out.println("Connection closed " + address);
                        System.exit(0);
                    }
                    System.out.println(address + ": " + msg);
                }

            } catch (IOException e) {
                e.printStackTrace();
            }

        }
    }

    private static class Write extends Thread {
        private Socket socket;

        public Write(Socket socket) {
            this.socket = socket;
        }

        public void run() {
            try {

                PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
                Scanner sc = new Scanner(System.in);
                String msg;

                while (true) {
                    msg = sc.nextLine();
                    out.println(msg);
                }

            } catch (IOException e) {
                e.printStackTrace();
            }

        }
    }

    public static void main(String[] args) throws IOException {
        PrintWriter out;
        BufferedReader in;
        Scanner sc = new Scanner(System.in);
        while (true) {  //for the test only
            Socket socket = null;
        try {   
            socket = new Socket("78.90.68.125", PORT);
        } catch(java.net.ConnectException e) {
            System.out.println("Connection error: host unreachable");
            System.exit(1);
        }
/*
        String address = socket.getInetAddress().toString().substring(1);
        System.out.println("Connection established " + address);
        Thread read = new Read(socket);     
        Thread write = new Write(socket);

        read.start();
        write.start();

        try {
            read.join();
            write.join();
        } catch(InterruptedException e) {
            e.printStackTrace();
        }
        finally {
*/      
        socket.close();
//      }
        //System.out.println("Connection closed " + address);
        }
    }
}

Answer 1

尝试制作

private static class Read extends Thread {
 private static Socket socket;
 private static String address;

和

private static class Write extends Thread {
 private static Socket socket;

到非静态。

另外，我不知道你是如何检查内存的，但请记住 Java 是垃圾收集的，你会看到最初的内存使用量增加，直到垃圾收集器 (GC) 收集它，并且会再次增加，直到下一次 GC 运行。所以它会持续增加很长一段时间没有任何下降，然后才会出现内存泄漏，否则你很高兴。

---

我按原样运行上述代码并运行了大约 1-2 小时，在使用 JDK 6 的 Mac 机器上稳定的内存使用量约为 54MB。我没有使用 jdk 附带的JConsole 来查看内存使用情况。我没有发现任何问题。

下面是我在回答中提到的图表，你有高峰和低谷..最后当我停止客户端时它是平坦的。

Answer 2

伊万，

使用线程的一些事情。

永远不要这样做：

 try {
   read.join();
   write.join();
 } catch(InterruptedException e) {
 }   

总是在 catch 子句中加入一些东西，比如 log.error。你没有机会知道它发生了。

然后，所有流/关闭等必须进入 finally 块。否则你永远无法确保关闭所有必要的东西。

您可能希望重用连接。尝试这个： http://commons.apache.org/pool/

您能否告诉我们您是否经常访问 sysout 以关闭连接？ 基本上每次打开连接和关闭连接时都尝试创建日志语句。可能你看到了你缺少的东西。

Answer 3

尝试将您的 socket.close() 放入 finally 块中以确保它运行。

但我认为您的代码可能存在更大的问题，因为您没有使用连接池，因此您不必要地打开新连接。