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file_locks.py
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109 lines (89 loc) · 3.5 KB
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# Copyright (c) Facebook, Inc. and its affiliates.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import print_function
import contextlib
import errno
import os
BUCK_LOCK_FILE_NAME = ".buck_lock"
if os.name == "posix":
import fcntl
def _fcntl_with_exception_handling(fh, exclusive, wait):
lock_type = fcntl.LOCK_EX if exclusive else fcntl.LOCK_SH
if not wait:
lock_type |= fcntl.LOCK_NB
try:
fcntl.lockf(fh.fileno(), lock_type)
return True
except IOError as e:
if e.errno in [errno.EACCES, errno.EAGAIN]:
return False
raise
else:
def _fcntl_with_exception_handling(fh, exclusive, wait):
return True
def acquire_shared_lock(fh, wait=False):
""" Acquires a shared posix advisory lock on a file in a non-blocking way. The f argument
should be a file (ideally opened with 'a+', as that works for both shared and exclusive locks).
Returns True on success, False if the lock cannot be taken, throws on error.
"""
return _fcntl_with_exception_handling(fh, exclusive=False, wait=wait)
@contextlib.contextmanager
def shared_lock(path, *args, **kwargs):
with open(path, "a+b") as fh:
if acquire_shared_lock(fh, *args, **kwargs):
yield fh
else:
raise OSError("Failed to acquire shared lock on %s" % path)
def acquire_exclusive_lock(fh, wait=False):
""" Acquires an exclusive posix advisory lock on a file in a non-blocking way. The f argument
should be a file (ideally opened with 'a+', as that works for both shared and exclusive locks).
Returns True on success, False if the lock cannot be taken, throws on error.
"""
return _fcntl_with_exception_handling(fh, exclusive=True, wait=wait)
@contextlib.contextmanager
def exclusive_lock(path, *args, **kwargs):
with open(path, "a+b") as fh:
if acquire_exclusive_lock(fh, *args, **kwargs):
yield fh
else:
raise OSError("Failed to acquire exclusive lock on %s" % path)
def rmtree_if_can_lock(root):
""" Removes the directory and sub-directories under root, except any directories which have
a `.buck_lock` file present, which are only deleted if an exclusive lock can be obtained on
the lock file.
"""
lock_file_path = os.path.join(root, BUCK_LOCK_FILE_NAME)
lock_file = None
if os.path.exists(lock_file_path):
lock_file = open(lock_file_path, "a+") # noqa: P201
if not acquire_exclusive_lock(lock_file):
lock_file.close()
return
for name in os.listdir(root):
p = os.path.join(root, name)
if os.path.isdir(p):
rmtree_if_can_lock(p)
else:
try:
os.unlink(p)
except OSError:
# Ignore errors like shutil.rmtree
pass
try:
os.rmdir(root)
except OSError:
# Ignore errors like shutil.rmtree
pass
if lock_file is not None:
lock_file.close()