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'''
Utility for simple distribution of work on multiple processes, by
making sure only one process is working on a job at once.
'''
import os, errno, socket, atexit, time, sys
def exit_if_job_done(directory):
if pidfile_taken(os.path.join(directory, 'lockfile.pid'), verbose=True):
sys.exit(0)
if os.path.isfile(os.path.join(directory, 'done.txt')):
with open(os.path.join(directory, 'done.txt')) as f:
msg = f.read()
print(msg)
sys.exit(0)
def mark_job_done(directory):
with open(os.path.join(directory, 'done.txt'), 'w') as f:
f.write('Done by %d@%s %s at %s' %
(os.getpid(), socket.gethostname(),
os.getenv('STY', ''),
time.strftime('%c')))
def pidfile_taken(path, verbose=False):
'''
Usage. To grab an exclusive lock for the remaining duration of the
current process (and exit if another process already has the lock),
do this:
if pidfile_taken('job_423/lockfile.pid', verbose=True):
sys.exit(0)
To do a batch of jobs, just run a script that does them all on
each available machine, sharing a network filesystem. When each
job grabs a lock, then this will automatically distribute the
jobs so that each one is done just once on one machine.
'''
# Try to create the file exclusively and write my pid into it.
try:
os.makedirs(os.path.dirname(path), exist_ok=True)
fd = os.open(path, os.O_CREAT | os.O_EXCL | os.O_RDWR)
except OSError as e:
if e.errno == errno.EEXIST:
# If we cannot because there was a race, yield the conflicter.
conflicter = 'race'
try:
with open(path, 'r') as lockfile:
conflicter = lockfile.read().strip() or 'empty'
except:
pass
if verbose:
print('%s held by %s' % (path, conflicter))
return conflicter
else:
# Other problems get an exception.
raise
# Register to delete this file on exit.
lockfile = os.fdopen(fd, 'r+')
atexit.register(delete_pidfile, lockfile, path)
# Write my pid into the open file.
lockfile.write('%d@%s %s\n' % (os.getpid(), socket.gethostname(),
os.getenv('STY', '')))
lockfile.flush()
os.fsync(lockfile)
# Return 'None' to say there was not a conflict.
return None
def delete_pidfile(lockfile, path):
'''
Runs at exit after pidfile_taken succeeds.
'''
if lockfile is not None:
try:
lockfile.close()
except:
pass
try:
os.unlink(path)
except:
pass
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