Sometimes it is useful to get the number of tasks currently holding the
semaphore. Currently, assuming that every call to acquire is paired with a
call to release in the same task (e.g. the semaphore is only used in
[async] with statements), one can do
INITIAL_VALUE - sem._value
where INITIAL_VALUE is the value that was used to construct the semaphore
and sem is the semaphore object. But, as the name indicates, `sem._value`
is intended for internal use only.
I would proposing exposing this value "officially" by adding a property:
@property
def count(self):
return self._initial_value - self._value
The implementation would probably have to be a bit more sophisticated than
this, because there can be spurious calls to .release() that aren't
actually releasing the semaphore because it was never acquired, and it
would need to be decided whether reentrant acquires of the semaphore in the
same task are counted separately or not.
Perhaps this could be added only to asyncio.BoundedSemaphore.
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