def _AttemptPseudoLockRelease(pseudo_lock_fd):
"""Try to release the pseudo lock and return a boolean indicating whether
the release was succesful.
This whole operation is guarded with the global cloud storage lock, which
prevents race conditions that might otherwise cause multiple processes to
believe they hold the same pseudo lock (see _FileLock for more details).
"""
pseudo_lock_path = pseudo_lock_fd.name
try:
with open(_CLOUD_STORAGE_GLOBAL_LOCK) as global_file:
with lock.FileLock(global_file, lock.LOCK_EX | lock.LOCK_NB):
lock.ReleaseFileLock(pseudo_lock_fd)
pseudo_lock_fd.close()
try:
os.remove(pseudo_lock_path)
except OSError:
# We don't care if the pseudo lock gets removed elsewhere before
# we have a chance to do so.
pass
return True
except (lock.LockException, IOError):
# We failed to acquire the global cloud storage lock and are thus unable to
# release the pseudo lock.
return False
def _FileLock(base_path):
pseudo_lock_path = '%s.pseudo_lock' % base_path
_CreateDirectoryIfNecessary(os.path.dirname(pseudo_lock_path))
# We need to make sure that there is no other process which is acquiring the
# lock on |base_path| and has not finished before proceeding further to create
# the |pseudo_lock_path|. Otherwise, |pseudo_lock_path| may be deleted by
# that other process after we create it in this process.
while os.path.exists(pseudo_lock_path):
time.sleep(0.1)
# Guard the creation & acquiring lock of |pseudo_lock_path| by the global lock
# to make sure that there is no race condition on creating the file.
with open(_CLOUD_STORAGE_GLOBAL_LOCK) as global_file:
with lock.FileLock(global_file, lock.LOCK_EX):
fd = open(pseudo_lock_path, 'w')
lock.AcquireFileLock(fd, lock.LOCK_EX)
try:
yield
finally:
lock.ReleaseFileLock(fd)
try:
fd.close()
os.remove(pseudo_lock_path)
except OSError:
# We don't care if the pseudo-lock gets removed elsewhere before we have
# a chance to do so.
pass
def testUnlockBeforeClosingFile(self):
tf = tempfile.NamedTemporaryFile(delete=False)
tf.close()
temp_status_file = tf.name
try:
with open(self.temp_file_path, 'r') as f:
lock.AcquireFileLock(f, lock.LOCK_SH)
lock.ReleaseFileLock(f)
p = multiprocessing.Process(
target=_ReadFileWithExclusiveLockNonBlocking,
args=(self.temp_file_path, temp_status_file))
p.start()
p.join()
with open(temp_status_file, 'r') as f:
self.assertEquals('LockException was not raised', f.read())
finally:
os.remove(temp_status_file)