raw_input and print in a thread

Question

I have a thread which can print some text on the console and the main program have a raw_input to control the thread.

My problem is when I'm writing and the thread too I get something like this:

-->whatiwWHATTHETHREADWRITErite

but I would like to get some thing like this

WHATTHETHREADWRITE
-->whatiwrite

Janne Karila · Accepted Answer · 2012-01-14 10:50:53Z

4

You can create a lock, and perform all input and output while holding the lock:

import threading

stdout_lock = threading.Lock()

with stdout_lock:
    r = raw_input()

with stdout_lock:
    print "something"

answered Jan 14, 2012 at 10:50

Janne Karila

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2 Comments

Rik Poggi Over a year ago

@Guillaume: Can I ask you how can this work for you? I thought that you needed the input channel to be left open to control the thread.

Guillaume Over a year ago

Yes I have make something like in your post!

Rik Poggi · Accepted Answer · 2012-01-14 11:53:39Z

You have to syncronize your input with the thread output preventing them from happening at the same time.

You can modify the main loop like:

lock = threading.lock()

while 1:
    raw_input()     # Waiting for you to press Enter
    with lock:
        r = raw_input('--> ')
        # send your command to the thread

And then lock the background thread printing:

def worker(lock, ...):
    [...]
    with lock:
        print('what the thread write')

In short when you Press Enter you will stop the thread and enter in "input mode".

To be more specific, every time you Press Enter you will:

wait for the lock to be available
acquire the lock
print --> and wait for your command
insert your command
send that command to the thread
release the lock

So your thread will be stopped only if it tries to print when you are in "input mode",
and in your terminal you'll get something like:

some previous output

---> your input
THE THREAD OUTPUT

Paulo Scardine · Accepted Answer · 2012-01-14 10:42:39Z

-1

Use something like curses to write the background task output to half the screen and your input/control stuff on the other half.

You can also fiddle with ANSI escape codes on most terminals.

answered Jan 14, 2012 at 10:42

Paulo Scardine

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