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From "Martin Sandiford (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (EXEC-63) Race condition in DefaultExecutor#execute(cmd, handler)
Date Thu, 23 Feb 2012 00:25:48 GMT

     [ https://issues.apache.org/jira/browse/EXEC-63?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Martin Sandiford updated EXEC-63:
---------------------------------

    Description: 
{{DefaultExecutor#execute(CommandLine, ExecuteResultHandler)}} can, and usually does, return
before the target process has actually started.  This can result in a race condition where
several asynchronous processes are coupled by {{PipedInputStream}}/{{PipedOutputStream}} objects.

The following example shows the issue:

{code:title=Borken.java|borderStyle=solid}
import java.io.*;
import org.apache.commons.exec.*;

public class Borken {
  public static int pipe(OutputStream out, OutputStream err, InputStream in, CommandLine cmd0,
CommandLine cmd1)
      throws IOException {
    PipedInputStream pipeIn = new PipedInputStream();
    PipedOutputStream pipeOut = new PipedOutputStream(pipeIn);
    DefaultExecutor exec0 = new DefaultExecutor();
    exec0.setStreamHandler(new PumpStreamHandler(pipeOut, null, in));
    exec0.execute(cmd0, new DefaultExecuteResultHandler());
    
    // If the following line is commented, deadlock occurs
    //try { Thread.sleep(100); } catch (InterruptedException e) { }

    DefaultExecutor exec1 = new DefaultExecutor();
    exec1.setStreamHandler(new PumpStreamHandler(out, err, pipeIn));
    return exec1.execute(cmd1);
  }
  
  public static void main(String... args) {
    CommandLine cmd0 = new CommandLine("cmd").addArgument("/c").addArgument("dir");
    //CommandLine cmd0 = new CommandLine("ls").addArgument("-l");
    CommandLine cmd1 = new CommandLine("sort");
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    ByteArrayOutputStream err = new ByteArrayOutputStream();
    ByteArrayInputStream in = new ByteArrayInputStream(new byte[0]);
    try {
      int result = pipe(out, err, in, cmd0, cmd1);
      System.out.format("Result code: %d%n", result);
      System.out.format("Out: %s%n", out.toString());
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}
{code}

One possible solution is to pass in a semaphore object into {{DefaultExecutor#executeInternal}}
which is notified once the process is started.  The {{execute(CommandLine, Map, ExecuteResultHandler)}}
method can then wait on this before returning.

  was:
DefaultExecutor#execute(CommandLine, ExecuteResultHandler) can, and usually does, return before
the target process has actually started.  This can result in a race condition where several
asynchronous processes are coupled by PipedInputStream/PipedOutputStream objects.

The following example shows the issue:

import java.io.*;
import org.apache.commons.exec.*;

public class Borken {
  public static int pipe(OutputStream out, OutputStream err, InputStream in, CommandLine cmd0,
CommandLine cmd1)
      throws IOException {
    PipedInputStream pipeIn = new PipedInputStream();
    PipedOutputStream pipeOut = new PipedOutputStream(pipeIn);
    DefaultExecutor exec0 = new DefaultExecutor();
    exec0.setStreamHandler(new PumpStreamHandler(pipeOut, null, in));
    exec0.execute(cmd0, new DefaultExecuteResultHandler());
    
    // If the following line is commented, deadlock occurs
    //try { Thread.sleep(100); } catch (InterruptedException e) { }

    DefaultExecutor exec1 = new DefaultExecutor();
    exec1.setStreamHandler(new PumpStreamHandler(out, err, pipeIn));
    return exec1.execute(cmd1);
  }
  
  public static void main(String... args) {
    CommandLine cmd0 = new CommandLine("cmd").addArgument("/c").addArgument("dir");
    //CommandLine cmd0 = new CommandLine("ls").addArgument("-l");
    CommandLine cmd1 = new CommandLine("sort");
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    ByteArrayOutputStream err = new ByteArrayOutputStream();
    ByteArrayInputStream in = new ByteArrayInputStream(new byte[0]);
    try {
      int result = pipe(out, err, in, cmd0, cmd1);
      System.out.format("Result code: %d%n", result);
      System.out.format("Out: %s%n", out.toString());
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

One possible solution is to pass in a semaphore object into DefaultExecutor#executeInternal
which is notified once the process is started.  The execute(CommandLine, Map, ExecuteResultHandler)
method can then wait on this before returning.

    
> Race condition in DefaultExecutor#execute(cmd, handler)
> -------------------------------------------------------
>
>                 Key: EXEC-63
>                 URL: https://issues.apache.org/jira/browse/EXEC-63
>             Project: Commons Exec
>          Issue Type: Bug
>    Affects Versions: 1.1
>         Environment: Windows 7/64 bit, JDK 1.6.0_27
>            Reporter: Martin Sandiford
>              Labels: deadlock
>   Original Estimate: 24h
>  Remaining Estimate: 24h
>
> {{DefaultExecutor#execute(CommandLine, ExecuteResultHandler)}} can, and usually does,
return before the target process has actually started.  This can result in a race condition
where several asynchronous processes are coupled by {{PipedInputStream}}/{{PipedOutputStream}}
objects.
> The following example shows the issue:
> {code:title=Borken.java|borderStyle=solid}
> import java.io.*;
> import org.apache.commons.exec.*;
> public class Borken {
>   public static int pipe(OutputStream out, OutputStream err, InputStream in, CommandLine
cmd0, CommandLine cmd1)
>       throws IOException {
>     PipedInputStream pipeIn = new PipedInputStream();
>     PipedOutputStream pipeOut = new PipedOutputStream(pipeIn);
>     DefaultExecutor exec0 = new DefaultExecutor();
>     exec0.setStreamHandler(new PumpStreamHandler(pipeOut, null, in));
>     exec0.execute(cmd0, new DefaultExecuteResultHandler());
>     
>     // If the following line is commented, deadlock occurs
>     //try { Thread.sleep(100); } catch (InterruptedException e) { }
>     DefaultExecutor exec1 = new DefaultExecutor();
>     exec1.setStreamHandler(new PumpStreamHandler(out, err, pipeIn));
>     return exec1.execute(cmd1);
>   }
>   
>   public static void main(String... args) {
>     CommandLine cmd0 = new CommandLine("cmd").addArgument("/c").addArgument("dir");
>     //CommandLine cmd0 = new CommandLine("ls").addArgument("-l");
>     CommandLine cmd1 = new CommandLine("sort");
>     ByteArrayOutputStream out = new ByteArrayOutputStream();
>     ByteArrayOutputStream err = new ByteArrayOutputStream();
>     ByteArrayInputStream in = new ByteArrayInputStream(new byte[0]);
>     try {
>       int result = pipe(out, err, in, cmd0, cmd1);
>       System.out.format("Result code: %d%n", result);
>       System.out.format("Out: %s%n", out.toString());
>     } catch (Exception e) {
>       e.printStackTrace();
>     }
>   }
> }
> {code}
> One possible solution is to pass in a semaphore object into {{DefaultExecutor#executeInternal}}
which is notified once the process is started.  The {{execute(CommandLine, Map, ExecuteResultHandler)}}
method can then wait on this before returning.

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