Doesn't fit 100% to your example but helps to understand the underlying issue: Process P starts child C. Child C writes something to its stdout. stdout of C is a pipe which has a 4096 character buffer and the output is shorter than that. Now, C waits for some input. For C, everything is fine.
P waits for the output which will never come because the OS sees no reason to flush the output buffer of C (with so little data in it). Since P never gets the output of C, it will never write anything to C, so C hangs waiting for the input from P.
Fix: Use flush after every write to a pipe forcing the OS to send the data now.
In your case, adding proc.stdin.flush()
in the main while loop and a sys.stdout.flush()
in the child loop after the print should fix your problem.
You should also consider moving the code which reads from the other process into a thread. The idea here is that you can never know when the data will arrive and using a thread helps you to understand these issues while you write the code which processes the results.
At this place, I wanted to show you the new Python 2.6 documentation but it doesn't explain the flush issue, either :( Oh well ...
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…