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| -rw-r--r-- | Doc/library/multiprocessing.rst | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst index b2ed544..3d1c209 100644 --- a/Doc/library/multiprocessing.rst +++ b/Doc/library/multiprocessing.rst @@ -1006,12 +1006,24 @@ inherited by child processes. ctypes type or a one character typecode of the kind used by the :mod:`array` module. *\*args* is passed on to the constructor for the type. - If *lock* is ``True`` (the default) then a new lock object is created to - synchronize access to the value. If *lock* is a :class:`Lock` or - :class:`RLock` object then that will be used to synchronize access to the - value. If *lock* is ``False`` then access to the returned object will not be - automatically protected by a lock, so it will not necessarily be - "process-safe". + If *lock* is ``True`` (the default) then a new recursive lock + object is created to synchronize access to the value. If *lock* is + a :class:`Lock` or :class:`RLock` object then that will be used to + synchronize access to the value. If *lock* is ``False`` then + access to the returned object will not be automatically protected + by a lock, so it will not necessarily be "process-safe". + + Operations like ``+=`` which involve a read and write are not + atomic. So if, for instance, you want to atomically increment a + shared value it is insufficient to just do :: + + counter.value += 1 + + Assuming the associated lock is recursive (which it is by default) + you can instead do :: + + with counter.get_lock(): + counter.value += 1 Note that *lock* is a keyword-only argument. |