Use a metaclass to implement the singleton pattern #340
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Reason
More correct implementation of the
singleton
pattern.There is a problem with the current implementation: class's
__init__
to be called again wheneverlock_class(is_singleton=True)
is called, which is at least not obvious (also, it'll lead to the re-initializing instance's internal objects, e.g.: virtualenv/util/lock.py)What was done in this PR
FileLockMeta
/AsyncFileLockMeta
used as metaclasses forBaseFileLock
/BaseAsyncFileLock
__init__
method is called only onceRelated PRs