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[WIP] bpo-30703: More reentrant signal handler #2408

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[WIP] bpo-30703: More reentrant signal handler #2408

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1 change: 1 addition & 0 deletions Include/ceval.h
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,7 @@ PyAPI_FUNC(int) PyEval_MergeCompilerFlags(PyCompilerFlags *cf);
#endif

PyAPI_FUNC(int) Py_AddPendingCall(int (*func)(void *), void *arg);
PyAPI_FUNC(void) _PyEval_SignalReceived(void);
PyAPI_FUNC(int) Py_MakePendingCalls(void);

/* Protection against deeply nested recursive calls
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2 changes: 1 addition & 1 deletion Modules/signalmodule.c
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Expand Up @@ -248,7 +248,7 @@ trip_signal(int sig_num)
/* Set is_tripped after setting .tripped, as it gets
cleared in PyErr_CheckSignals() before .tripped. */
is_tripped = 1;
Py_AddPendingCall(checksignals_witharg, NULL);
_PyEval_SignalReceived();
}

/* And then write to the wakeup fd *after* setting all the globals and
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15 changes: 15 additions & 0 deletions Python/ceval.c
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Expand Up @@ -387,13 +387,28 @@ Py_AddPendingCall(int (*func)(void *), void *arg)
return result;
}

void
_PyEval_SignalReceived(void)
{
/* bpo-30703: Function called when the C signal handler of Python gets a
signal. We cannot queue a callback using Py_AddPendingCall() since this
function is not reentrant (use a lock and a list). */
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s/use/uses/

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Also say "signal-safe" rather than "reentrant", since otherwise it's not clear how Py_AddPendingCall can be called reentrantly.

SIGNAL_PENDING_CALLS();
}

int
Py_MakePendingCalls(void)
{
static int busy = 0;
int i;
int r = 0;

/* Python signal handler doesn't really queue a callback: it only signals
that an UNIX signal was received, see _PyEval_SignalReceived(). */
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You can remove "UNIX", as even Windows has a couple of signals :-)

if (PyErr_CheckSignals() < 0) {
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Perhaps this should be called after the check for main_thread and busy?

return -1;
}

if (!pending_lock) {
/* initial allocation of the lock */
pending_lock = PyThread_allocate_lock();
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