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import fcntl
import os
class SemaphoreAcquireError(Exception):
pass
class Semaphore:
def __init__(self, semaphore_file):
self.semaphore_file = semaphore_file
self.semaphore_fd = None
def __enter__(self):
# create the semaphore file if it does not exist
if not os.path.exists(self.semaphore_file):
open(self.semaphore_file, "w").close()
# open the file descriptor for the semaphore file
self.semaphore_fd = os.open(self.semaphore_file, os.O_CREAT)
try:
fcntl.flock(self.semaphore_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
except OSError:
raise SemaphoreAcquireError("Could not acquire semaphore lock")
def __exit__(self, exc_type, exc_value, traceback):
# release the semaphore
fcntl.flock(self.semaphore_fd, fcntl.LOCK_UN)
# close the file descriptor
os.close(self.semaphore_fd)
# reset the file descriptor to None
self.semaphore_fd = None
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