Message4794

I am using the popen2.popen2 function to open a child and get a pipe to
him. Unfortunatelly when i print to the pipe the child does not get any
output.
Unfortunatelly i dont have internet connection in the computer i work
with so i am not able to submit exactly the same program that caused the
error, however i will post here some similar code, as similar as my
memory allows.

<Code>
1:  child_stdout, chld_stdin = popen("/usr/bin/tee")
2:  child_stdin.write("This is a line\n")
3:  child_stdin.flush()
4:  out = child_stdout.readline()
5:  print "from child:", out
</code>

The code above should print “from child: This is a line” because tee
prints back its line it receives. The code works as it should in cpython
but in jython it gets stucked in line 4 when trying to read. 
The problem in jython is that the pipe is not flushed to ‘tee’, ‘tee’
gets not input and consequently it does not print back any value. Thus
trying to read from child_stdout blocks the program to the end of the days.
I have been doing some debugging and the problem seems to happen also
with subprocess.Popen
Since I have not enough knowledge of jython and the Popen implementation
I cannot tell exactly what is the problem. In spite of that, I still
could understand some of the code and I see that the pipe is implemented
as a python file wrapping an object of type org.python.core.io.StreamIO
wrapping the output stream returned by
‘java.lang.Process.getOutputStream(..)’ . I copied-pasted that code and
 to a function of mine and tried to play with it. I arrived at the
conclution that there are two places to flush.
The jython file handler has a flush function and the java output stream
has another flush function that never gets flushed, that means that even
when the jython file is not buffered, output is never printed. 
This pseudo-code will do the work that the previous pseudo-code should
have done:
<code>
procBuild = java.lang.ProcessBuilder(["/usr/bin/tee"])
proc = procBuild.start()
proc_out = proc.getOutputStream()
child_stdout = org.python.core.io.StreamIO (proc_out, True) #copied True
from the Popen code
child_stdin = org.python.core.io.StreamIO (proc.getInputStream()
, True)
 child_stdin.write("This is a line\n")
 child_stdin.flush()
proc_out.flush() #NOTICE THIS LINE!!!
out = child_stdout.readline()
print "from child:", out
</code>