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# Copyright The OpenTelemetry Authors
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from threading import Lock
from typing import Callable
class Once:
"""Execute a function exactly once and block all callers until the function returns
Same as golang's `sync.Once <https://pkg.go.dev/sync#Once>`_
"""
def __init__(self) -> None:
self._lock = Lock()
self._done = False
def do_once(self, func: Callable[[], None]) -> bool:
"""Execute ``func`` if it hasn't been executed or return.
Will block until ``func`` has been called by one thread.
Returns:
Whether or not ``func`` was executed in this call
"""
# fast path, try to avoid locking
if self._done:
return False
with self._lock:
if not self._done:
func()
self._done = True
return True
return False
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