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import psutil
import filelock
def can_spawn_tahoe(pidfile):
"""
Determine if we can spawn a Tahoe-LAFS for the given pidfile. That
pidfile may be deleted if it is stale.
:param pathlib.Path pidfile: the file to check, that is the Path
to "running.process" in a Tahoe-LAFS configuration directory
:returns bool: True if we can spawn `tahoe run` here
"""
lockpath = pidfile.parent / (pidfile.name + ".lock")
with filelock.FileLock(lockpath):
try:
with pidfile.open("r") as f:
pid, create_time = f.read().strip().split(" ", 1)
except FileNotFoundError:
return True
# somewhat interesting: we have a pidfile
pid = int(pid)
create_time = float(create_time)
try:
proc = psutil.Process(pid)
# most interesting case: there _is_ a process running at the
# recorded PID -- but did it just happen to get that PID, or
# is it the very same one that wrote the file?
if create_time == proc.create_time():
# _not_ stale! another intance is still running against
# this configuration
return False
except psutil.NoSuchProcess:
pass
# the file is stale
pidfile.unlink()
return True
from pathlib import Path
print("can spawn?", can_spawn_tahoe(Path("running.process")))
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