Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.8/site-packages/opentelemetry/util/_once.py: 47%

1# Copyright The OpenTelemetry Authors 

2# 

3# Licensed under the Apache License, Version 2.0 (the "License"); 

4# you may not use this file except in compliance with the License. 

5# You may obtain a copy of the License at 

6# 

7# http://www.apache.org/licenses/LICENSE-2.0 

8# 

9# Unless required by applicable law or agreed to in writing, software 

10# distributed under the License is distributed on an "AS IS" BASIS, 

11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 

12# See the License for the specific language governing permissions and 

13# limitations under the License. 

14 

15from threading import Lock 

16from typing import Callable 

17 

18 

19class Once: 

20 """Execute a function exactly once and block all callers until the function returns 

21 

22 Same as golang's `sync.Once <https://pkg.go.dev/sync#Once>`_ 

23 """ 

24 

25 def __init__(self) -> None: 

26 self._lock = Lock() 

27 self._done = False 

28 

29 def do_once(self, func: Callable[[], None]) -> bool: 

30 """Execute ``func`` if it hasn't been executed or return. 

31 

32 Will block until ``func`` has been called by one thread. 

33 

34 Returns: 

35 Whether or not ``func`` was executed in this call 

36 """ 

37 

38 # fast path, try to avoid locking 

39 if self._done: 

40 return False 

41 

42 with self._lock: 

43 if not self._done: 

44 func() 

45 self._done = True 

46 return True 

47 return False