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1# Copyright The OpenTelemetry Authors
2# SPDX-License-Identifier: Apache-2.0
4from collections.abc import Callable
5from threading import Lock
8class Once:
9 """Execute a function exactly once and block all callers until the function returns
11 Same as golang's `sync.Once <https://pkg.go.dev/sync#Once>`_
12 """
14 def __init__(self) -> None:
15 self._lock = Lock()
16 self._done = False
18 def do_once(self, func: Callable[[], None]) -> bool:
19 """Execute ``func`` if it hasn't been executed or return.
21 Will block until ``func`` has been called by one thread.
23 Returns:
24 Whether or not ``func`` was executed in this call
25 """
27 # fast path, try to avoid locking
28 if self._done:
29 return False
31 with self._lock:
32 if not self._done:
33 func()
34 self._done = True
35 return True
36 return False