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Posted to issues@commons.apache.org by "Martin Sandiford (Updated) (JIRA)" <ji...@apache.org> on 2012/02/23 01:25:48 UTC
[jira] [Updated] (EXEC-63) Race condition in
DefaultExecutor#execute(cmd, handler)
[ 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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