From d823eee619c0e7c1a9bc5b0caa0d0fa4734ac052 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mat=C4=9Bj=20Cepl?= <mcepl@cepl.eu>
Date: Thu, 23 May 2019 22:30:00 +0200
Subject: [PATCH] bpo-23395: Fix PyErr_SetInterrupt if the SIGINT signal is
 ignored or not handled (GH-7778)
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``_thread.interrupt_main()`` now avoids setting the Python error status if the ``SIGINT`` signal is ignored or not handled by Python.
(cherry picked from commit 608876b6b1eb59538e6c29671a733033fb8b5be7)

Co-authored-by: Matěj Cepl <mcepl@cepl.eu>
---
 Doc/c-api/exceptions.rst                      | 12 +++----
 Doc/library/_thread.rst                       |  8 +++--
 Lib/test/test_threading.py                    | 35 +++++++++++++++++++
 Misc/ACKS                                     |  2 +-
 .../2016-07-27-11-06-43.bpo-23395.MuCEX9.rst  |  2 ++
 Modules/signalmodule.c                        | 13 ++++---
 6 files changed, 59 insertions(+), 13 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2016-07-27-11-06-43.bpo-23395.MuCEX9.rst

--- a/Doc/c-api/exceptions.rst
+++ b/Doc/c-api/exceptions.rst
@@ -504,13 +504,13 @@ Signal Handling
       single: SIGINT
       single: KeyboardInterrupt (built-in exception)
 
-   This function simulates the effect of a :const:`SIGINT` signal arriving --- the
-   next time :c:func:`PyErr_CheckSignals` is called,  :exc:`KeyboardInterrupt` will
-   be raised.  It may be called without holding the interpreter lock.
-
-   .. % XXX This was described as obsolete, but is used in
-   .. % _thread.interrupt_main() (used from IDLE), so it's still needed.
+   Simulate the effect of a :const:`SIGINT` signal arriving. The next time
+   :c:func:`PyErr_CheckSignals` is called,  the Python signal handler for
+   :const:`SIGINT` will be called.
 
+   If :const:`SIGINT` isn't handled by Python (it was set to
+   :data:`signal.SIG_DFL` or :data:`signal.SIG_IGN`), this function does
+   nothing.
 
 .. c:function:: int PySignal_SetWakeupFd(int fd)
 
--- a/Doc/library/_thread.rst
+++ b/Doc/library/_thread.rst
@@ -57,8 +57,12 @@ It defines the following constants and f
 
 .. function:: interrupt_main()
 
-   Raise a :exc:`KeyboardInterrupt` exception in the main thread.  A subthread can
-   use this function to interrupt the main thread.
+   Simulate the effect of a :data:`signal.SIGINT` signal arriving in the main
+   thread. A thread can use this function to interrupt the main thread.
+
+   If :data:`signal.SIGINT` isn't handled by Python (it was set to
+   :data:`signal.SIG_DFL` or :data:`signal.SIG_IGN`), this function does
+   nothing.
 
 
 .. function:: exit()
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -16,6 +16,7 @@ import unittest
 import weakref
 import os
 import subprocess
+import signal
 
 from test import lock_tests
 from test import support
@@ -1162,6 +1163,7 @@ class BoundedSemaphoreTests(lock_tests.B
 class BarrierTests(lock_tests.BarrierTests):
     barriertype = staticmethod(threading.Barrier)
 
+
 class MiscTestCase(unittest.TestCase):
     def test__all__(self):
         extra = {"ThreadError"}
@@ -1169,5 +1171,38 @@ class MiscTestCase(unittest.TestCase):
         support.check__all__(self, threading, ('threading', '_thread'),
                              extra=extra, blacklist=blacklist)
 
+
+class InterruptMainTests(unittest.TestCase):
+    def test_interrupt_main_subthread(self):
+        # Calling start_new_thread with a function that executes interrupt_main
+        # should raise KeyboardInterrupt upon completion.
+        def call_interrupt():
+            _thread.interrupt_main()
+        t = threading.Thread(target=call_interrupt)
+        with self.assertRaises(KeyboardInterrupt):
+            t.start()
+            t.join()
+        t.join()
+
+    def test_interrupt_main_mainthread(self):
+        # Make sure that if interrupt_main is called in main thread that
+        # KeyboardInterrupt is raised instantly.
+        with self.assertRaises(KeyboardInterrupt):
+            _thread.interrupt_main()
+
+    def test_interrupt_main_noerror(self):
+        handler = signal.getsignal(signal.SIGINT)
+        try:
+            # No exception should arise.
+            signal.signal(signal.SIGINT, signal.SIG_IGN)
+            _thread.interrupt_main()
+
+            signal.signal(signal.SIGINT, signal.SIG_DFL)
+            _thread.interrupt_main()
+        finally:
+            # Restore original handler
+            signal.signal(signal.SIGINT, handler)
+
+
 if __name__ == "__main__":
     unittest.main()
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -248,7 +248,7 @@ Donn Cave
 Charles Cazabon
 Jesús Cea Avión
 Per Cederqvist
-Matej Cepl
+Matěj Cepl
 Carl Cerecke
 Octavian Cerna
 Michael Cetrulo
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2016-07-27-11-06-43.bpo-23395.MuCEX9.rst
@@ -0,0 +1,2 @@
+``_thread.interrupt_main()`` now avoids setting the Python error status
+if the ``SIGINT`` signal is ignored or not handled by Python.
--- a/Modules/signalmodule.c
+++ b/Modules/signalmodule.c
@@ -1561,13 +1561,18 @@ PyErr_CheckSignals(void)
 }
 
 
-/* Replacements for intrcheck.c functionality
- * Declared in pyerrors.h
- */
+/* Simulate the effect of a signal.SIGINT signal arriving. The next time
+   PyErr_CheckSignals is called,  the Python SIGINT signal handler will be
+   raised.
+
+   Missing signal handler for the SIGINT signal is silently ignored. */
 void
 PyErr_SetInterrupt(void)
 {
-    trip_signal(SIGINT);
+    if ((Handlers[SIGINT].func != IgnoreHandler) &&
+        (Handlers[SIGINT].func != DefaultHandler)) {
+        trip_signal(SIGINT);
+    }
 }
 
 void