Java ProcessBuilder: external process hangs

I'm using Java's ProcessBuilder class to run an external process. The process should not terminate before the Java program does; it must stay alive in command/response mode.

I know that the process streams may easily 'jam' if neglected, so I've done the following: The program reads the process's combined output and error streams in a "reader" thread, and uses a "writer" thread to manage the commands. The reader thread does blocking character reads from process output, buffers them up into Strings and dispatches the results. The writer thread writes complete "command" lines via a PrintWriter; it uses a queue to ensure that no two command writes are "too close together" (currently 100ms), and that no new command gets written before the output of the previous command i开发者_如何转开发s complete. I also call flush() and checkError() after every println().

This scheme works fine for a few seconds or minutes, then the reader thread hangs on the blocking read(). No errors, no exceptions thrown, no more process output. Thereafter nothing will revive the external process (short of restarting it). (BTW this happens on both Linux and Windows.)

I've looked at the code and test-cases in Jakarta Commons Exec and in Plexus Utils http://plexus.codehaus.org/plexus-utils/ but (a) neither gives an example of using a long-lived Process and (b) neither appears to be doing anything basically different from what I've described.

Does anyone have a clue what's happening here please? Thanks!

Do you also have a thread managing stderr? You only mention the two streams.

i had implemented error, input and output stream in three sepereate threads and i can read and write to external processes without any problem.

I tested both on windows/linux with multitude of built in apps cmd/bash as well as other cmd line binaries and it works fine except on some occasions it just throws io stream exception, what i do is catch the exception and restart thread again, so that program keeps on working.

If you are trying to e.g ssh in linux, then you might run across problem like you won't be able to write to same stdin, this is because of security reasons.

Try taking input from System.in and see if it works, it worked in my case

Just a guess, but have you tried un-combining the error and output streams?