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