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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() | |