mirror of https://github.com/apache/cloudstack.git
72 lines
2.7 KiB
Python
72 lines
2.7 KiB
Python
# Licensed to the Apache Software Foundation (ASF) under one
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# or more contributor license agreements. See the NOTICE file
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# distributed with this work for additional information
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# regarding copyright ownership. The ASF licenses this file
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# to you under the Apache License, Version 2.0 (the
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# "License"); you may not use this file except in compliance
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# with the License. You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing,
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# software distributed under the License is distributed on an
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# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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# KIND, either express or implied. See the License for the
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# specific language governing permissions and limitations
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# under the License.
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import threading
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from typing import Dict, NamedTuple
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class _ImageState(NamedTuple):
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read_sem: threading.Semaphore
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write_sem: threading.Semaphore
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lock: threading.Lock
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class ConcurrencyManager:
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"""
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Manages per-image read/write semaphores and per-image mutual-exclusion locks.
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Each image_id gets its own independent pool of read slots (default MAX_PARALLEL_READS)
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and write slots (default MAX_PARALLEL_WRITES), so concurrent transfers to different images
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do not contend with each other.
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The per-image lock serialises operations that must not overlap on the
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same image (e.g. flush while writing, extents while writing).
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"""
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def __init__(self, max_reads: int, max_writes: int):
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self._max_reads = max_reads
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self._max_writes = max_writes
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self._images: Dict[str, _ImageState] = {}
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self._guard = threading.Lock()
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def _state_for(self, image_id: str) -> _ImageState:
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with self._guard:
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state = self._images.get(image_id)
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if state is None:
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state = _ImageState(
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read_sem=threading.Semaphore(self._max_reads),
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write_sem=threading.Semaphore(self._max_writes),
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lock=threading.Lock(),
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)
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self._images[image_id] = state
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return state
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def acquire_read(self, image_id: str, blocking: bool = False) -> bool:
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return self._state_for(image_id).read_sem.acquire(blocking=blocking)
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def release_read(self, image_id: str) -> None:
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self._state_for(image_id).read_sem.release()
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def acquire_write(self, image_id: str, blocking: bool = False) -> bool:
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return self._state_for(image_id).write_sem.acquire(blocking=blocking)
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def release_write(self, image_id: str) -> None:
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self._state_for(image_id).write_sem.release()
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def get_image_lock(self, image_id: str) -> threading.Lock:
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return self._state_for(image_id).lock
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