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bpo-42296: On Windows, fix CTRL+C regression (GH-23257) 

On Windows, fix a regression in signal handling which prevented to
interrupt a program using CTRL+C. The signal handler can be run in a
thread different than the Python thread, in which case the test
deciding if the thread can handle signals is wrong.

On Windows, _PyEval_SignalReceived() now always sets eval_breaker to
1 since it cannot test _Py_ThreadCanHandleSignals(), and
  eval_frame_handle_pending() always calls
  _Py_ThreadCanHandleSignals() to recompute eval_breaker.
This commit is contained in:
Victor Stinner 2020-11-13 14:44:42 +01:00 committed by GitHub
parent 0cec97eb6a
commit d96a7a8313
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2 changed files with 37 additions and 5 deletions
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4
Misc/NEWS.d/next/Core and Builtins/2020-11-13-13-53-11.bpo-42296.DuGrLJ.rst Normal file
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@ -0,0 +1,4 @@
On Windows, fix a regression in signal handling which prevented to interrupt
a program using CTRL+C. The signal handler can be run in a thread different
than the Python thread, in which case the test deciding if the thread can
handle signals is wrong.

34
Python/ceval.c
View File

@ -203,13 +203,18 @@ UNSIGNAL_PENDING_CALLS(PyInterpreterState *interp)
static inline void
SIGNAL_PENDING_SIGNALS(PyInterpreterState *interp)
SIGNAL_PENDING_SIGNALS(PyInterpreterState *interp, int force)
{
struct _ceval_runtime_state *ceval = &interp->runtime->ceval;
struct _ceval_state *ceval2 = &interp->ceval;
_Py_atomic_store_relaxed(&ceval->signals_pending, 1);
if (force) {
_Py_atomic_store_relaxed(&ceval2->eval_breaker, 1);
}
else {
/* eval_breaker is not set to 1 if thread_can_handle_signals() is false */
COMPUTE_EVAL_BREAKER(interp, ceval, ceval2);
}
}
@ -559,10 +564,22 @@ PyEval_RestoreThread(PyThreadState *tstate)
void
_PyEval_SignalReceived(PyInterpreterState *interp)
{
#ifdef MS_WINDOWS
// bpo-42296: On Windows, _PyEval_SignalReceived() is called from a signal
// handler which can run in a thread different than the Python thread, in
// which case _Py_ThreadCanHandleSignals() is wrong. Ignore
// _Py_ThreadCanHandleSignals() and always set eval_breaker to 1.
//
// The next eval_frame_handle_pending() call will call
// _Py_ThreadCanHandleSignals() to recompute eval_breaker.
int force = 1;
#else
int force = 0;
#endif
/* bpo-30703: Function called when the C signal handler of Python gets a
signal. We cannot queue a callback using _PyEval_AddPendingCall() since
that function is not async-signal-safe. */
SIGNAL_PENDING_SIGNALS(interp);
SIGNAL_PENDING_SIGNALS(interp, force);
}
/* Push one item onto the queue while holding the lock. */
@ -662,7 +679,7 @@ handle_signals(PyThreadState *tstate)
UNSIGNAL_PENDING_SIGNALS(tstate->interp);
if (_PyErr_CheckSignalsTstate(tstate) < 0) {
/* On failure, re-schedule a call to handle_signals(). */
SIGNAL_PENDING_SIGNALS(tstate->interp);
SIGNAL_PENDING_SIGNALS(tstate->interp, 0);
return -1;
}
return 0;
@ -948,6 +965,17 @@ eval_frame_handle_pending(PyThreadState *tstate)
return -1;
}
#ifdef MS_WINDOWS
// bpo-42296: On Windows, _PyEval_SignalReceived() can be called in a
// different thread than the Python thread, in which case
// _Py_ThreadCanHandleSignals() is wrong. Recompute eval_breaker in the
// current Python thread with the correct _Py_ThreadCanHandleSignals()
// value. It prevents to interrupt the eval loop at every instruction if
// the current Python thread cannot handle signals (if
// _Py_ThreadCanHandleSignals() is false).
COMPUTE_EVAL_BREAKER(tstate->interp, ceval, ceval2);
#endif
return 0;
}