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bpo-30703: Improve signal delivery (#2415)

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* Improve signal delivery

Avoid using Py_AddPendingCall from signal handler, to avoid calling signal-unsafe functions.

* Remove unused function

* Improve comments

* Add stress test

* Adapt for --without-threads

* Add second stress test

* Add NEWS blurb

* Address comments @haypo
This commit is contained in:
Antoine Pitrou 2017-06-28 23:29:29 +02:00 • committed by GitHub
parent 9f3bdcb643
commit c08177a1cc
5 changed files with 171 additions and 37 deletions
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30
Modules/signalmodule.c
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@ -188,12 +188,6 @@ The default handler for SIGINT installed by Python.\n\
It raises KeyboardInterrupt.");
static int
checksignals_witharg(void * unused)
{
return PyErr_CheckSignals();
}
static int
report_wakeup_write_error(void *data)
{
@ -244,17 +238,15 @@ trip_signal(int sig_num)
Handlers[sig_num].tripped = 1;
if (!is_tripped) {
/* Set is_tripped after setting .tripped, as it gets
cleared in PyErr_CheckSignals() before .tripped. */
is_tripped = 1;
Py_AddPendingCall(checksignals_witharg, NULL);
}
/* Set is_tripped after setting .tripped, as it gets
cleared in PyErr_CheckSignals() before .tripped. */
is_tripped = 1;
_PyEval_SignalReceived();
/* And then write to the wakeup fd *after* setting all the globals and
doing the Py_AddPendingCall. We used to write to the wakeup fd and then
set the flag, but this allowed the following sequence of events
(especially on windows, where trip_signal runs in a new thread):
doing the _PyEval_SignalReceived. We used to write to the wakeup fd
and then set the flag, but this allowed the following sequence of events
(especially on windows, where trip_signal may run in a new thread):
- main thread blocks on select([wakeup_fd], ...)
- signal arrives
@ -289,6 +281,8 @@ trip_signal(int sig_num)
wakeup.send_err_set = 1;
wakeup.send_errno = errno;
wakeup.send_win_error = GetLastError();
/* Py_AddPendingCall() isn't signal-safe, but we
still use it for this exceptional case. */
Py_AddPendingCall(report_wakeup_send_error, NULL);
}
}
@ -302,6 +296,8 @@ trip_signal(int sig_num)
rc = _Py_write_noraise(fd, &byte, 1);
if (rc < 0) {
/* Py_AddPendingCall() isn't signal-safe, but we
still use it for this exceptional case. */
Py_AddPendingCall(report_wakeup_write_error,
(void *)(intptr_t)errno);
}
@ -1556,8 +1552,10 @@ PyErr_CheckSignals(void)
arglist);
Py_DECREF(arglist);
}
if (!result)
if (!result) {
is_tripped = 1;
return -1;
}
Py_DECREF(result);
}