I have one process who's reading from a file (using file.read()) and one process who's writing to the same file (file.write()). The problem is it doesn't work - I get no errors but they can't operate at the same time. I've tried making the read and write operations none-blocking and then flushing the stream, as follows:
fcntl.fcntl(file, fcntl.F_SETFL, os.O_NONBLOCK)
file.write(msg)
file.flush()
Am I completely misunderstanding it? How should one accomplish writing and reading to one file from different processes?
test1.py
import os
f = open('txt.txt', 'a', os.O_NONBLOCK)
while 1:
f.write('asd')
f.flush()
test2.py
import os
f = open('txt.txt', 'r', os.O_NONBLOCK)
while 1:
print f.read(3)
This works fine for me.
Is there a reason to use a common file? Inter-process communication is probably much easier using sockets.
Take a look at this Read-Write Lock class:
- http://code.activestate.com/recipes/502283-read-write-lock-class-rlock-like/
and at this articles about locking and threading:
- http://effbot.org/zone/thread-synchronization.htm
- http://linuxgazette.net/107/pai.html
Another great way to do this is to use a pipe
This example instantiates a pipe, which returns a reader and a writer object. Then one process writes to the pipe using the writer and the other reads from it using the reader.
Python os.pipe(): https://docs.python.org/3/library/os.html#os.pipe
