[issue30844] selectors: Add exceptional urgent data event

[STINNER Victor]

STINNER Victor added the comment:

> To be able to use GPIO Sysfs Interface on our embedded platforms we require exceptional event support.

Antoine Pitrou noticed that "exception" term can be confusion in Python, since exceptions are like "raise ValueError(...)".

The manual page mentions "out-of-band (OOB) data".

http://man7.org/linux/man-pages/man2/select_tut.2.html

       exceptfds
              This set is watched for "exceptional conditions".  In
              practice, only one such exceptional condition is common: the
              availability of out-of-band (OOB) data for reading from a TCP
              socket.  See recv(2), send(2), and tcp(7) for more details
              about OOB data.  (One other less common case where select(2)
              indicates an exceptional condition occurs with pseudoterminals
              in packet mode; see ioctl_tty(2).)  After select() has
              returned, exceptfds will be cleared of all file descriptors
              except for those for which an exceptional condition has
              occurred.

Is it what you need for a GPIO? GPIO is unrelated to TCP, right?

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nosy: +haypo

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<http://bugs.python.org/issue30844>
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