在Java輸入/輸出流上使用BufferedReader時，readline（）會阻塞

Question

我正在制作一個Java（版本控制）應用程序，其中客戶端和服務器通過套接字流進行通信。 我遇到的問題是，客戶端或服務器在執行readline（）時經常傾向於阻塞，最終也會導致另一端也阻塞。 奇怪的是，第一次運行似乎沒有發生該錯誤。

我花了很多時間來找出導致問題的原因以及如何解決問題，但是我只能將問題簡化為下面提供的代碼。 MAKE_STUB參數允許使用管道流而不是套接字流。 它通常會導致在客戶端完成讀取之前關閉線程時導致的錯誤，但是有時也會發生與使用套接字時相同的錯誤，這大概表明問題不是由套接字的濫用引起的，而是流的濫用引起的。 ？

我還嘗試了以下操作：更改刷新輸出的時間，在println（）中添加+“ \\ n”，依次發送/接收（PING_PONG），防止流被垃圾收集（使用靜態列表），發送一個字符串而不是JSON等。我發現奇怪的是，這些解決方案只會導致該塊發生在更早或更晚的時間。

客戶代碼：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.UnknownHostException;


public class TestClientProt {

private static final boolean MAKE_STUB = false;
private static final boolean PING_PONG = false;


private static void send(String value, InputStream rawInput, OutputStream rawOutput) throws IOException {
    PrintWriter output = new PrintWriter(rawOutput);
    output.println(value);
    output.flush();

    if(PING_PONG) {
        BufferedReader input = new BufferedReader(new InputStreamReader(rawInput));
        if(!input.readLine().equals(value))
            System.err.println("Ping pong failed!");
    }
}


private static int receiveInt(InputStream rawInput, OutputStream rawOutput) throws NumberFormatException, IOException {
    return Integer.parseInt(receiveString(rawInput, rawOutput));
}

private static String receiveString(InputStream rawInput, OutputStream rawOutput) throws IOException {
    BufferedReader input = new BufferedReader(new InputStreamReader(rawInput));
    String value = input.readLine();

    if(PING_PONG) {
        PrintWriter output = new PrintWriter(rawOutput);
        output.println(value);
        output.flush();
    }

    return value;
}


public static void main(String[] args) throws IOException {
    Socket socket;

    InputStream rawInput;
    OutputStream rawOutput;

    if(MAKE_STUB) {

        rawInput = new PipedInputStream();
        final OutputStream rawServerOutput = new PipedOutputStream((PipedInputStream) rawInput);

        final PipedInputStream rawServerInput = new PipedInputStream();
        rawOutput = new PipedOutputStream(rawServerInput);

        new Thread() {

            public void run() {
                try {
                    TestServerProt.startSession(rawServerInput, rawServerOutput);
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

        }.start();


    } else {

        InetAddress ip = InetAddress.getByName("127.0.0.1");
        int port = 6789;

        InetSocketAddress serverAddress = new InetSocketAddress(ip, port);      
        socket = new Socket();
        socket.connect(serverAddress);

        rawInput = socket.getInputStream();
        rawOutput = socket.getOutputStream();

    }


    System.out.println("start checkout");

    send("CHKT repname", rawInput, rawOutput);
    System.out.println(receiveInt(rawInput, rawOutput));

    send("RREV", rawInput, rawOutput);
    System.out.println(receiveInt(rawInput, rawOutput));
    System.out.println("receiving revision");
    System.out.println(receiveString(rawInput, rawOutput));
    System.out.println("revision received");

    System.out.println(receiveInt(rawInput, rawOutput));
    System.out.println("receiving files");

    send("RFIL", rawInput, rawOutput);
    System.out.println(receiveInt(rawInput, rawOutput));
    System.out.println("receiving file: ");
    System.out.println(receiveString(rawInput, rawOutput));

    System.out.println("success!");


    if(!MAKE_STUB)
        socket.close();
}

}

服務器代碼：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
import java.net.Socket;

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;


public class TestServerProt {

private static final boolean PING_PONG = false;


public static void startSession(InputStream rawInput, OutputStream rawOutput) throws IOException {
    System.out.println("starting session");
    System.out.println(receiveString(rawInput, rawOutput));

    send(101, rawInput, rawOutput);

    System.out.println(receiveString(rawInput, rawOutput));
    System.out.println("sending revision");
    send(104, rawInput, rawOutput);
    send(createRepString(), rawInput, rawOutput);

    System.out.println("sending files");
    send(101, rawInput, rawOutput);
    System.out.println("sending files");

    System.out.println(receiveString(rawInput, rawOutput));
    send(103, rawInput, rawOutput);
    send("content file 1", rawInput, rawOutput);

    System.out.println("success!");

    //send(rCode);
}


private static void send(String value, InputStream rawInput, OutputStream rawOutput) throws IOException {
    PrintWriter output = new PrintWriter(rawOutput);
    output.println(value);
    output.flush();

    if(PING_PONG) {
        BufferedReader input = new BufferedReader(new InputStreamReader(rawInput));
        if(!input.readLine().equals(value))
            System.err.println("Ping pong failed!");
    }
}

private static void send(int value, InputStream rawInput, OutputStream rawOutput) throws IOException {
    send(String.valueOf(value), rawInput, rawOutput);
}


private static int receiveInt(InputStream rawInput, OutputStream rawOutput) throws NumberFormatException, IOException {
    return Integer.parseInt(receiveString(rawInput, rawOutput));
}

private static String receiveString(InputStream rawInput, OutputStream rawOutput) throws IOException {
    BufferedReader input = new BufferedReader(new InputStreamReader(rawInput));
    String value = input.readLine();

    if(PING_PONG) {
        PrintWriter output = new PrintWriter(rawOutput);
        output.println(value);
        output.flush();
    }

    return value;
}


public static void main(String[] args) throws IOException {
    int port = 6789;

    InetSocketAddress serverAddress = new InetSocketAddress(port);
    ServerSocket serverSocket = new ServerSocket();
    serverSocket.bind(serverAddress);

    System.out.println("waiting for client");

    Socket clientSocket = serverSocket.accept();

    System.out.println("client accepted");

    startSession(clientSocket.getInputStream(), clientSocket.getOutputStream());

    serverSocket.close();
    clientSocket.close();
}

private static String createRepString() {
    JSONObject json = new JSONObject();

    json.put("revision_nr", new Integer(5));

    JSONArray jsonArrayContent = new JSONArray();
    JSONObject jsonContent = new JSONObject();

    jsonContent.put("filename", "f1.txt");
    jsonContent.put("revision_nr", 3);
    jsonArrayContent.add(jsonContent);

    jsonContent.put("filename", "f2.txt");
    jsonContent.put("revision_nr", 1);
    jsonArrayContent.add(jsonContent);

    jsonContent.put("filename", "f3.txt");
    jsonContent.put("revision_nr", 5);
    jsonArrayContent.add(jsonContent);

    json.put("content", jsonArrayContent);

    JSONArray jsonArrayStatus = new JSONArray();
    JSONObject jsonStatus = new JSONObject();

    json.put("status", jsonArrayStatus);

    return json.toJSONString();
}

}

Answer 1

對於您而言，最重要的問題是每次閱讀時都創建一個新的BufferedReader 。 問題在於BufferedReader將用可用數據填充其整個緩沖區-因為它應該這樣做。 因此，它將從該行末尾的基礎流中讀取。

解決方案很簡單：只創建一次BufferedReader ，然后傳遞它，而不是InputStream 。