I haven't play with the thread stuff in Python (yet) but in general terms (from a C mind), one should not expect read/write actions to be sequential across threads. I would assume the Python threads eventually goes back to some system calls for thread handling. If that were the case, you should not be surprised at all that the I/O sequences appear to be quite unpredictable.
If you absolutely, positively wants them to come out in a certain way, you need to build in additionally serialization mechanisims in your code (like use semaphores and stuff). "Steven Bethard" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > I'm playing around with some threading stuff right now, and I'm having a > little trouble calling a function from one thread that affects another. > Here's my setup: > > py> import os, threading, time > py> def write(file_in, input_lines): > ... for line in input_lines: > ... time.sleep(0.5) > ... file_in.write(line) > ... file_in.flush() > ... file_in.close() > ... > py> def read(file_out, output_list): > ... while True: > ... line = file_out.readline() > ... if not line: > ... break > ... output_list.append(line) > ... > py> def runthreads(lst): > ... file_in, file_out, file_err = os.popen3('cat') > ... write_thread = threading.Thread( > ... target=write, args=(file_in, > ... ['%s\n' % x for x in range(10)])) > ... read_thread = threading.Thread(target=read, > ... args=(file_out, lst)) > ... write_thread.start() > ... read_thread.start() > ... write_thread.join() > ... read_thread.join() > ... > > Basically, I start one thread to read and one thread to write (from a > os.pipe). This all works fine for me: > > py> lst = [] > py> runthreads(lst) > py> lst > ['0\n', '1\n', '2\n', '3\n', '4\n', '5\n', '6\n', '7\n', '8\n', '9\n'] > > I run into a problem though when I try to call an update method every > time I read a line: > > py> class updatinglist(list): > ... def __init__(self, updater): > ... super(updatinglist, self).__init__() > ... self.updater = updater > ... def append(self, item): > ... super(updatinglist, self).append(item) > ... self.updater(len(self)) > ... > py> def update(i): > ... print i > ... > py> lst = updatinglist(update) > py> runthreads(lst) > 1 > 2 > 3 > 4 > 5 > 6 > 7 > 8 > 9 > 10 > py> lst > ['0\n', '1\n', '2\n', '3\n', '4\n', '5\n', '6\n', '7\n', '8\n', '9\n'] > > I get the correct output, but if you run this yourself, you'll see that > the numbers 1 through 10 aren't printed in sync with the writes (i.e. > every half second); they're all printed at the end. Could someone > explain to me why this happens, and how (if possible) I can get the > numbers printed in sync with the appends to the list? > > Thanks, > > Steve -- http://mail.python.org/mailman/listinfo/python-list
