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import threading
from types import TracebackType
from typing import Optional, Type
class ReadWriteLock:
"""A lock object that allows many simultaneous "read locks", but
only one "write lock." """
def __init__(self) -> None:
self._read_ready = threading.Condition(threading.RLock())
self._readers = 0
def acquire_read(self) -> None:
"""Acquire a read lock. Blocks only if a thread has
acquired the write lock."""
self._read_ready.acquire()
try:
self._readers += 1
finally:
self._read_ready.release()
def release_read(self) -> None:
"""Release a read lock."""
self._read_ready.acquire()
try:
self._readers -= 1
if not self._readers:
self._read_ready.notifyAll()
finally:
self._read_ready.release()
def acquire_write(self) -> None:
"""Acquire a write lock. Blocks until there are no
acquired read or write locks."""
self._read_ready.acquire()
while self._readers > 0:
self._read_ready.wait()
def release_write(self) -> None:
"""Release a write lock."""
self._read_ready.release()
class ReadRWLock:
def __init__(self, rwLock: ReadWriteLock):
self.rwLock = rwLock
def __enter__(self) -> None:
self.rwLock.acquire_read()
def __exit__(
self,
exc_type: Optional[Type[BaseException]],
exc_value: Optional[BaseException],
traceback: Optional[TracebackType],
) -> None:
self.rwLock.release_read()
class WriteRWLock:
def __init__(self, rwLock: ReadWriteLock):
self.rwLock = rwLock
def __enter__(self) -> None:
self.rwLock.acquire_write()
def __exit__(
self,
exc_type: Optional[Type[BaseException]],
exc_value: Optional[BaseException],
traceback: Optional[TracebackType],
) -> None:
self.rwLock.release_write()
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