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| -rw-r--r-- | Doc/library/ctypes.rst | 18 |
1 files changed, 12 insertions, 6 deletions
diff --git a/Doc/library/ctypes.rst b/Doc/library/ctypes.rst index ae10b71..f46da85 100644 --- a/Doc/library/ctypes.rst +++ b/Doc/library/ctypes.rst @@ -1022,12 +1022,18 @@ As we can easily check, our array is sorted now:: 1 5 7 33 99 >>> -**Important note for callback functions:** - -Make sure you keep references to :func:`CFUNCTYPE` objects as long as they are -used from C code. :mod:`ctypes` doesn't, and if you don't, they may be garbage -collected, crashing your program when a callback is made. - +.. note:: + + Make sure you keep references to :func:`CFUNCTYPE` objects as long as they + are used from C code. :mod:`ctypes` doesn't, and if you don't, they may be + garbage collected, crashing your program when a callback is made. + + Also, note that if the callback function is called in a thread created + outside of Python's control (e.g. by the foreign code that calls the + callback), ctypes creates a new dummy Python thread on every invocation. This + behavior is correct for most purposes, but it means that values stored with + `threading.local` will *not* survive across different callbacks, even when + those calls are made from the same C thread. .. _ctypes-accessing-values-exported-from-dlls: |