[New-bugs-announce] [issue18885] handle EINTR in the stdlib

[Charles-François Natali]

New submission from Charles-François Natali:

As discussed in http://mail.python.org/pipermail/python-dev/2013-August/128204.html, I think that we shouldn't let EINTR leak to Python code: it should be handled properly by the C code, so that users (and the Python part of the stdlib) don't have to worry about this low-level historical nuisance.

For code that doesn't release the GIL, we could simply use this glibc macro:
# define TEMP_FAILURE_RETRY(expression) \
  (__extension__                                                              \
    ({ long int __result;                                                     \
       do __result = (long int) (expression);                                 \
       while (__result == -1L && errno == EINTR);                             \
       __result; }))
#endif

Now, I'm not sure about how to best handle this for code that releases the GIL.

Basically:

    Py_BEGIN_ALLOW_THREADS
    pid = waitpid(pid, &status, options);
    Py_END_ALLOW_THREADS

should become

begin_handle_eintr:
        Py_BEGIN_ALLOW_THREADS
        pid = waitpid(pid, &status, options);
        Py_END_ALLOW_THREADS

        if (pid < 0 && errno == EINTR) {
            if (PyErr_CheckSignals())
                return NULL;
            goto begin_handle_eintr;
        }

Should we do this with a macro?

If yes, should it be a new one that should be placed around Py_BEGIN_ALLOW_THREADS/Py_END_ALLOW_THREADS (like BEGIN_SELECT_LOOP in selectmodule.c) or could we have a single macro that would do both (i.e. release the GIL / reacquire the GIL, and try again in case of EINTR, unless a signal handler raised an exception)?

>From a cursory look, the main files affected would be:
Modules/fcntlmodule.c
Modules/ossaudiodev.c
Modules/posixmodule.c
Modules/selectmodule.c
Modules/selectmodule.c
Modules/signalmodule.c
Modules/socketmodule.c
Modules/syslogmodule.c

----------
messages: 196555
nosy: neologix
priority: normal
severity: normal
stage: needs patch
status: open
title: handle EINTR in the stdlib
type: enhancement
versions: Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue18885>
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