java.lang/11

[green@cygnus.com]

The following reply was made to PR java.lang/11; it has been noted by GNATS.

From: green@cygnus.com
To: bryce@albatross.co.nz, java-gnats@sourceware.cygnus.com
Cc:  
Subject: Re: java.lang/11
Date: 5 Mar 2000 21:01:48 -0000

 Synopsis: Process inputstream/errorstream can block
 
 State-Changed-From-To: open->feedback
 State-Changed-By: green
 State-Changed-When: Sun Mar  5 13:01:48 2000
 State-Changed-Why:
     This is normal behaviour.  The comp.lang.java.programmer FAQ 
     says:
     6. (Sect. 18) How do I execute a command from Java?
     
          [*] Use
     
              Runtime.getRuntime().exec( myCommandString )
     
     
          where myCommandString is something like "/full/pathname/command". An
          applet will need to be signed in order to allow this.
     
          Note, there is a gotcha associated with reading output from commands.
          When the runtime exec's the process, it passes to it 3 streams, for
          stdin, stdout, and stderr; the out and err are buffered but the buffer
          size isn't very big. When your process runs, it reads (if needed) from
          in, and writes to out and err. If it doesn't write more than the
          buffer-size, it can run to completion.
     
          But if it tries to write more data to one or the other stream than the
          buffer can hold, the write blocks, and your process hangs, waiting for
          you to empty the buffer so it can write some more.
     
          So after the exec call, get the streams, and read from them in a loop
          until they both hit end-of-stream (don't block on either one, just read
          whatever is available from each, each loop iteration). Then when the
          streams have ended, call the process.waitFor() method to let it finish
          dying.
     
     
     I have a test program that exhibits the failure mode
     with the JDK, but not with GCJ.
     
     I think we should just close this one.
     
     
 
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