[Chicago] help with file locking

[Massimo Di Pierro]

Thank you! This helps a lot.

Massimo


On Feb 29, 2012, at 12:38 PM, Dan McGee wrote:

> On Wed, Feb 29, 2012 at 12:28 PM, Dan McGee <dpmcgee at gmail.com> wrote:
>> On Wed, Feb 29, 2012 at 11:50 AM, Massimo Di Pierro
>> <mdipierro at cs.depaul.edu> wrote:
>>> Hello everybody. I am stuck with a problem:
>
>>        lock(fp, fcntl.LOCK_EX, pn) # exclusive lock
>
> That new 'pn' argument came from some debugging I had in to track the
> process pool number. Full revised script code below.
>
> -Dan
>
>
> #!/usr/bin/env python
> # -*- coding: utf-8 -*-
> import fcntl
> import multiprocessing
> import unittest
>
> N=10000
>
> def lock(fp, mode, pn):
>    fcntl.flock(fp, mode)
>
> def unlock(fp, pn):
>    fcntl.flock(fp, fcntl.LOCK_UN)
>
> def read_write(args):
>    (filename, iterations, pn) = args
>    for i in range(0, iterations):
>        fp = open(filename, 'r')
>        lock(fp, fcntl.LOCK_SH, pn) # shared lock
>        content = fp.read()
>        unlock(fp, pn)              # unlock
>        fp.close()
>        if len(content) != N:
>            return len(content)
>        fp = open(filename, 'a')
>        lock(fp, fcntl.LOCK_EX, pn) # exclusive lock
>        fp.seek(0)
>        fp.truncate()
>        fp.write(content)
>        fp.flush()
>        unlock(fp, pn)              # unlock
>        fp.close()
>    return len(content)
>
> class TestParallelLocks(unittest.TestCase):
>
>    def setUp(self):
>        self.filename = 'test.txt'
>        contents = 'x' * N
>        fp = open(self.filename,'w')
>        fp.write(contents)
>        fp.close()
>
>    def tearDown(self):
>        try:
>            os.remove(self.filename)
>        except:
>            pass
>
>    def test_reads_and_writes(self):
>        readwriters = 10
>        pool = multiprocessing.Pool(processes = readwriters)
>        args = [[self.filename, 10, i] for i in range(readwriters)]
>        results = pool.map(read_write, args)
>        for result in results:
>            self.assertEqual(N, result)
>
> if __name__ == '__main__':
>    unittest.main(verbosity=2)
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