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from __future__ import annotations
import contextlib
import errno
import sys
from typing import Callable
from typing import Generator
if sys.platform == 'win32': # pragma: no cover (windows)
import msvcrt
# https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/locking
# on windows we lock "regions" of files, we don't care about the actual
# byte region so we'll just pick *some* number here.
_region = 0xffff
@contextlib.contextmanager
def _locked(
fileno: int,
blocked_cb: Callable[[], None],
) -> Generator[None, None, None]:
try:
msvcrt.locking(fileno, msvcrt.LK_NBLCK, _region)
except OSError:
blocked_cb()
while True:
try:
msvcrt.locking(fileno, msvcrt.LK_LOCK, _region)
except OSError as e:
# Locking violation. Returned when the _LK_LOCK or _LK_RLCK
# flag is specified and the file cannot be locked after 10
# attempts.
if e.errno != errno.EDEADLOCK:
raise
else:
break
try:
yield
finally:
# From cursory testing, it seems to get unlocked when the file is
# closed so this may not be necessary.
# The documentation however states:
# "Regions should be locked only briefly and should be unlocked
# before closing a file or exiting the program."
msvcrt.locking(fileno, msvcrt.LK_UNLCK, _region)
else: # pragma: win32 no cover
import fcntl
@contextlib.contextmanager
def _locked(
fileno: int,
blocked_cb: Callable[[], None],
) -> Generator[None, None, None]:
try:
fcntl.flock(fileno, fcntl.LOCK_EX | fcntl.LOCK_NB)
except OSError: # pragma: no cover (tests are single-threaded)
blocked_cb()
fcntl.flock(fileno, fcntl.LOCK_EX)
try:
yield
finally:
fcntl.flock(fileno, fcntl.LOCK_UN)
@contextlib.contextmanager
def lock(
path: str,
blocked_cb: Callable[[], None],
) -> Generator[None, None, None]:
with open(path, 'a+') as f:
with _locked(f.fileno(), blocked_cb):
yield
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