Java - 多個並發runtime.exec（）InputStreams的問題

Question

我別無選擇，只能通過對VBScript的幾個Runtime.exec()調用來檢索一些外部數據。 我真的很討厭這種實現，因為我失去了跨平台的靈活性，但我最終可能會開發類似的* nix腳本來至少緩解這個問題。 有人問之前，我無法解決需要調用外部腳本來收集我的數據。 我會忍受導致的問題。

exec()進程在擴展Runnable的自定義類中運行。 它使用BufferedReader從getInputStream()讀入數據。

編輯 ：更多的代碼按要求添加，但我不知道額外的代碼是如何相關的:)我希望它有所幫助，因為它需要一段時間來格式化！ 哦，如果它的丑陋，我的代碼風格變得容易，但鼓勵建設性的批評......

public class X extends JFrame implements Runnable {

   ...
   static final int THREADS_MAX = 4;
   ExecutorService  exec;
   ...
   public static void main(String[] args) {
      ...
      SwingUtilities.invokeLater(new X("X"));
   } // End main(String[])

   public X (String title) {
      ...
      exec = Executors.newFixedThreadPool(THREADS_MAX);
      ...

      // Create all needed instances of Y
      for (int i = 0; i < objects.length; i++) {
         Y[i] = new Y(i);
      } // End for(i)

      // Initialization moved here for easy single-thread testing
      // Undesired, of course
      for (int i = 0; i < objects.length; i++) {
         Y[i].initialize(parent);
      } // End for(i)

   } // End X

   class Y implements Runnable {
      // Define variables/arrays used to capture data here
      String computerName = "";
      ...

      public Y(int rowIndex) {
         row          = rowIndex;
         ...
         computerName = (String)JTable.getValueAt(row, 0);
         ...
         exec.execute(this);
      } // End Y(int)

      public void run() {
         // Initialize variables/arrays used to capture data here
         ...

         // Initialization should be done here for proper threading
         //initialize(parent);
      } // End run()

      public void initialize(Z obj) {
         runTime = Runtime.getRuntime();
         ...

         try {
            process = runTime.exec("cscript.exe query.vbs " + computerName);
            stdErr  = process.getErrorStream();
            stdIn   = process.getInputStream();
            isrErr  = new InputStreamReader(stdErr);
            isrIn   = new InputStreamReader(stdIn);
            brErr   = new BufferedReader(isrErr);
            brIn    = new BufferedReader(isrIn);

            while ((line = brIn.readLine()) != null) {
               // Capture, parse, and store data here
               ...
            } // End while

         } catch (IOException e) {
            System.out.println("Unable to run script");
         } catch (Exception e) {
            e.printStackTrace();
         } finally {
            try {
               stdErr.close();
               stdIn. close();
               isrErr.close();
               isrIn. close();
               brErr. close();
               brIn.  close();
            } catch (IOException e) {
               System.out.println("Unable to close streams.");
            } // End try
         } // End try
      } // End initialize(Z)
      ...
   } // End class Y
} // End class X

如果我單獨執行命令，我會按預期收集數據。 但是，如果我在類的run()塊中執行命令（意味着調用是並發的，正如我所希望的那樣），則看起來好像只生成了一個輸入流，所有BufferedReaders都會並發使用。

為了調試這個問題，我在控制台上輸出每個消耗的行，前面是我的類的哪個實例正在讀取輸入流。 我期待類似下面的內容，理解它們可能在實例到實例之間出現故障，但單個實例的行順序將完好無損：

exec 0: Line1
exec 1: Line1
exec 2: Line1
exec 0: Line2
exec 1: Line2
exec 2: Line2
exec 0: Line3
exec 1: Line3
exec 2: Line3
...

奇怪的是，我獲得了輸出第一行的預期實例數（ Microsoft (R) Windows Script Host Version 5.7 ），但在此行之后，只有一個進程繼續在輸入流中生成數據，並且所有讀者隨機使用這一個流，例如：

exec 2: Microsoft (R) Windows Script Host Version 5.7
exec 0: Microsoft (R) Windows Script Host Version 5.7
exec 1: Microsoft (R) Windows Script Host Version 5.7
exec 0: line2
exec 1: line3
exec 2: line4
...

更糟糕的是，讀者停止並且readLine()永遠不會返回null。 我讀到這種行為可能與緩沖區大小有關，但是當我只運行兩個並發線程時，即使輸出很短，它仍然表現出相同的行為。 stdErr沒有捕獲任何stdErr以指示存在問題。

為了查看這是否是腳本主機的限制，我創建了一個批處理文件，該文件同時START多個腳本實例。 我應該聲明這是在 Java 之外的cmd shell中運行的，並啟動了幾個自己的shell。 但是，每個並發實例完全返回預期結果並且表現良好。

編輯：作為另一個故障排除的想法，我決定重新啟用並發，但通過在Y.run()塊中插入以下內容來錯開我的初始化方法：

try {
   Thread.sleep((int)(Math.random() * 1200));
} catch (InterruptedException e) {
   System.out.println("Can't sleep!");
} // End try
initialize(monitor);

進入我的代碼。 我開始看到前幾行的多個輸出，但很快就會回復到消費同一個生產者的多個消費者，並且一旦第一個完成的流關閉，其余的消費者就會觸發異常。 下一個使用者觸發IOException: Read error ，其余消息觸發IOException: Stream closed ！

根據maaartinus，可以運行多個並發的InputStreams ，所以現在問題變成導致不良行為的原因了嗎？ 如何獨立獲取輸入流？ 我不想寫一個臨時文件只是為了處理數據，如果我可以避免它。

Answer 1

我認為你需要注意IO變量的范圍。 這是一個非常好用的快速代碼，來自4個子進程的並發輸入流......

import java.io.*;

public class MultiExec {

        private final static String[] comLines = {
                        "date",
                        "ls /var/spool/postfix",
                        "ls -F /usr/local/bin",
                        "wc -l /etc/apache2/apache2.conf"};

        public void execute() {
                for (int i = 0 ; i < comLines.length ; i++) {
                        ExecutableChild ec = new ExecutableChild (i, comLines[i]);
                        new Thread (ec).start();
        }}

        public class ExecutableChild implements Runnable {

                private int prIndex;
                private String executable;

                public ExecutableChild (int k, String cmd) {
                        prIndex = k;
                        executable = cmd;
                }

                public void run () {
                        try {
                                Process child = Runtime.getRuntime().exec(executable);
                                BufferedReader br = new BufferedReader (new InputStreamReader (
                                                                child.getInputStream()));
                                for (String s = br.readLine() ; s != null ; s = br.readLine())
                                        System.out.println ("[" + prIndex + "] " + s);
                                br.close();
                        } catch (IOException ioex) {
                                System.err.println ("IOException for process #"+
                                                prIndex+ ": " + ioex.getMessage());
        }}}

        public static void main (String[] args) {
                new MultiExec().execute();
        }
}

上面代碼的輸出（％javac MultiExec.java; java MultiExec）

[2] tomcat*
[0] Thu Jan 20 18:38:31 CST 2011
[3] 368 /etc/apache2/apache2.conf
[1] active
[1] bounce
[1] corrupt
[1] defer
[1] deferred
[1] etc
[1] flush
[1] hold
[1] incoming
[1] lib
[1] maildrop
[1] pid
[1] private
[1] public
[1] saved
[1] trace
[1] usr
[1] var

如果您向我們提供了您嘗試的源代碼，我們可以進行討論。 祝福， - MS

================================================== ===========================

編輯：DN：我理解您對1行輸出的擔憂。 讓我們有一個小腳本......

#!/usr/bin/perl -w
foreach (1..50) {
        print "$_\n";
}

以及上述Java代碼的編輯版本... comLines已更改，並且每個println（）后添加了Thread.sleep

公共類MultiExec {

        private final static String[] comLines = {
                        "ls /var/spool/postfix",
                        "perl count50.pl",
                        "cat MultiExec.java",
                        "head -40 /etc/apache2/apache2.conf"};

        public void execute() {
                for (int i = 0 ; i < comLines.length ; i++) {
                        ExecutableChild ec = new ExecutableChild (i, comLines[i]);
                        new Thread (ec).start();
        }}

        public class ExecutableChild implements Runnable {

                private int prIndex;
                private String executable;

                public ExecutableChild (int k, String cmd) {
                        prIndex = k;
                        executable = cmd;
                }

                public void run () {
                        try {
                                Process child = Runtime.getRuntime().exec(executable);
                                BufferedReader br = new BufferedReader (new InputStreamReader (
                                                                child.getInputStream()));
                                for (String s = br.readLine() ; s != null ; s = br.readLine()) {
                                        System.out.println ("[" + prIndex + "] " + s);
                                        try {
                                                Thread.sleep (20);
                                        } catch (InterruptedException intex) {
                                }}
                                br.close();
                        } catch (IOException ioex) {
                                System.err.println ("IOException for process #"+
                                                                prIndex+ ": " + ioex.getMessage());
        }}}

        public static void main (String[] args) {
                new MultiExec().execute();
}}

這是現在的輸出（在編譯/運行之后）......

[0] active
[1] 1
[2] import java.io.*;
[3] #
[2]
[0] bounce
[1] 2
[3] # Based upon the NCSA server configuration files originally by Rob McCool.
[2] public class MultiExec {
[1] 3
[0] corrupt
[3] #
[1] 4
[2]
[0] defer
[3] # This is the main Apache server configuration file.  It contains the
[2]     private final static String[] comLines = {
[0] deferred
[1] 5
[3] # configuration directives that give the server its instructions.
[2]                     "ls /var/spool/postfix",
[0] etc
[1] 6
[3] # See http://httpd.apache.org/docs/2.2/ for detailed information about
[2]                     "perl count50.pl",
[0] flush
[1] 7
[3] # the directives.
[2]                     "cat MultiExec.java",
[1] 8
[0] hold
[3] #
[1] 9
[2]                     "head -40 /etc/apache2/apache2.conf"};
[0] incoming
[3] # Do NOT simply read the instructions in here without understanding
[2]
[0] lib
[1] 10
[3] # what they do.  They're here only as hints or reminders.  If you are unsure
[1] 11
[2]     public void execute() {
[0] maildrop
[3] # consult the online docs. You have been warned.
[2]             for (int i = 0 ; i < comLines.length ; i++) {
[0] pid
[1] 12
[3] #
[1] 13
[2]                     ExecutableChild ec = new ExecutableChild (i, comLines[i]);
[0] private
[3] # The configuration directives are grouped into three basic sections:
[1] 14
[2]                     new Thread (ec).start();
[0] public
[3] #  1. Directives that control the operation of the Apache server process as a
[2]     }}
[1] 15
[0] saved
[3] #     whole (the 'global environment').
[1] 16
[0] trace
[2]
[3] #  2. Directives that define the parameters of the 'main' or 'default' server,
[0] usr
[2]     public class ExecutableChild implements Runnable {
[1] 17
[3] #     which responds to requests that aren't handled by a virtual host.
[0] var
[2]
[1] 18
[3] #     These directives also provide default values for the settings
[1] 19
[2]             private int prIndex;
[3] #     of all virtual hosts.
[1] 20
[2]             private String executable;
[3] #  3. Settings for virtual hosts, which allow Web requests to be sent to
[2]
[1] 21
[3] #     different IP addresses or hostnames and have them handled by the
[1] 22
[2]             public ExecutableChild (int k, String cmd) {
[3] #     same Apache server process.
[1] 23
[2]                     prIndex = k;
[3] #
[1] 24
[2]                     executable = cmd;
[3] # Configuration and logfile names: If the filenames you specify for many
[2]             }
[1] 25
[3] # of the server's control files begin with "/" (or "drive:/" for Win32), the
[2]
[1] 26
[3] # server will use that explicit path.  If the filenames do *not* begin
[1] 27
[2]             public void run () {
[3] # with "/", the value of ServerRoot is prepended -- so "/var/log/apache2/foo.log"
[1] 28
[2]                     try {
[3] # with ServerRoot set to "" will be interpreted by the
[1] 29
[2]                             Process child = Runtime.getRuntime().exec(executable);
[3] # server as "//var/log/apache2/foo.log".
[1] 30
[2]                             BufferedReader br = new BufferedReader (new InputStreamReader (
[3] #
[1] 31
[2]                                                             child.getInputStream()));
[3]
[1] 32
[2]                             for (String s = br.readLine() ; s != null ; s = br.readLine()) {
[3] ### Section 1: Global Environment
[1] 33
[2]                                     System.out.println ("[" + prIndex + "] " + s);
[3] #
[1] 34
[2]                                     try {
[3] # The directives in this section affect the overall operation of Apache,
[1] 35
[2]                                             Thread.sleep (20);
[3] # such as the number of concurrent requests it can handle or where it

......

輸入流工作正常，不要認為我在這里有問題。 很抱歉回復這么長時間。 祝你最好，等着看你的代碼， - MS

Answer 2

確保在正確的范圍內聲明stdErr和stdIn 。 在這種情況下，您需要在Y聲明它們。

如果您在X中聲明它們，則每次運行以下代碼時：

stdErr  = process.getErrorStream();
stdIn   = process.getInputStream();

將重新分配變量， Y所有實例將引用相同的流。