def fork(nprocs=None):
'''continue as ``nprocs`` parallel processes by forking ``nprocs-1`` times
If ``nprocs`` exceeds the configured ``maxprocs`` than it will silently be
capped. It is up to the user to prepare shared memory and/or locks for
inter-process communication. As a safety measure nested forks are blocked by
limiting nprocs to 1; all secondary forks will be silently ignored.
'''
if nprocs is None or nprocs > _maxprocs.value:
nprocs = _maxprocs.value
if nprocs <= 1:
yield 0
return
if not hasattr(os, 'fork'):
warnings.warn('fork is unavailable on this platform')
yield 0
return
amchild = False
try:
child_pids = []
for procid in builtins.range(1, nprocs):
pid = os.fork()
if not pid: # pragma: no cover
amchild = True
signal.signal(
signal.SIGINT,
signal.SIG_IGN) # disable sigint (ctrl+c) handler
treelog.current = treelog.NullLog() # silence treelog
break
child_pids.append(pid)
else:
procid = 0
with maxprocs(1):
yield procid
except BaseException as e:
if amchild: # pragma: no cover
try:
print('[parallel.fork] exception in child process:', e)
finally:
os._exit(1) # communicate failure to main process
for pid in child_pids: # kill all child processes
os.kill(pid, signal.SIGKILL)
raise
else:
if amchild: # pragma: no cover
os._exit(0) # communicate success to main process
with treelog.context('waiting for child processes'):
nfails = sum(not _wait(pid) for pid in child_pids)
if nfails: # failure in child process: raise exception
raise Exception('fork failed in {} out of {} processes'.format(
nfails, nprocs))
finally:
if amchild: # pragma: no cover
os._exit(1) # failsafe
def fork(nprocs=None):
'''continue as ``nprocs`` parallel processes by forking ``nprocs-1`` times
If ``nprocs`` exceeds the configured ``maxprocs`` than it will silently be
capped. It is up to the user to prepare shared memory and/or locks for
inter-process communication. As a safety measure nested forks are blocked by
limiting nprocs to 1; all secondary forks will be silently ignored.
'''
if nprocs is None or nprocs > _maxprocs:
nprocs = _maxprocs
if nprocs == 1:
yield 0
return
if not hasattr(os, 'fork'):
log.warning('fork is unavailable on this platform')
yield 0
return
child_pids = []
try:
fail = 1
for procid in builtins.range(1, nprocs):
pid = os.fork()
if not pid:
signal.signal(
signal.SIGINT,
signal.SIG_IGN) # disable sigint (ctrl+c) handler
log.current = log.NullLog()
break
child_pids.append(pid)
else:
procid = 0
with maxprocs(1):
yield procid
fail = 0
finally:
if procid: # before anything else can fail:
os._exit(fail) # communicate exit status to main process
nfails = fail + sum(os.waitpid(pid, 0)[1] != 0 for pid in child_pids)
if fail: # failure in main process: exception has been reraised
log.error(
'fork failed in {} out of {} processes; reraising exception for main process'
.format(nfails, nprocs))
elif nfails: # failure in child process: raise exception
raise Exception('fork failed in {} out of {} processes'.format(
nfails, _maxprocs))
def output_tester(self):
with self.assertSilent():
yield treelog.NullLog()