Backport PR #12137: Fix inability to interrupt processes on Windows

IPython/utils/_process_win32.py

@@ -18,10 +18,12 b' This file is only meant to be imported by process.py, not by end-users.'
 import os
 import sys
 import ctypes
+import time
 
 from ctypes import c_int, POINTER
 from ctypes.wintypes import LPCWSTR, HLOCAL
-from subprocess import STDOUT
+from subprocess import STDOUT, TimeoutExpired
+from threading import Thread
 
 # our own imports
 from ._process_common import read_no_interrupt, process_handler, arg_split as py_arg_split
@@ -93,15 +95,29 b' def _find_cmd(cmd):'
 def _system_body(p):
     """Callback for _system."""
     enc = DEFAULT_ENCODING
-    for line in read_no_interrupt(p.stdout).splitlines():
-        line = line.decode(enc, 'replace')
-        print(line, file=sys.stdout)
-    for line in read_no_interrupt(p.stderr).splitlines():
-        line = line.decode(enc, 'replace')
-        print(line, file=sys.stderr)
 
-    # Wait to finish for returncode
-    return p.wait()
+    def stdout_read():
+        for line in read_no_interrupt(p.stdout).splitlines():
+            line = line.decode(enc, 'replace')
+            print(line, file=sys.stdout)
+
+    def stderr_read():
+        for line in read_no_interrupt(p.stderr).splitlines():
+            line = line.decode(enc, 'replace')
+            print(line, file=sys.stderr)
+
+    Thread(target=stdout_read).start()
+    Thread(target=stderr_read).start()
+
+    # Wait to finish for returncode. Unfortunately, Python has a bug where
+    # wait() isn't interruptible (https://bugs.python.org/issue28168) so poll in
+    # a loop instead of just doing `return p.wait()`.
+    while True:
+        result = p.poll()
+        if result is None:
+            time.sleep(0.01)
+        else:
+            return result
 
 
 def system(cmd):
@@ -116,9 +132,7 b' def system(cmd):'
 
     Returns
     -------
-    None : we explicitly do NOT return the subprocess status code, as this
-    utility is meant to be used extensively in IPython, where any return value
-    would trigger :func:`sys.displayhook` calls.
+    int : child process' exit code.
     """
     # The controller provides interactivity with both
     # stdin and stdout

IPython/utils/tests/test_process.py

@@ -15,13 +15,19 b' Tests for platutils.py'
 #-----------------------------------------------------------------------------
 
 import sys
+import signal
 import os
+import time
+from _thread import interrupt_main  # Py 3
+import threading
+from unittest import SkipTest
 
 import nose.tools as nt
 
 from IPython.utils.process import (find_cmd, FindCmdError, arg_split,
                                    system, getoutput, getoutputerror,
                                    get_output_error_code)
+from IPython.utils.capture import capture_output
 from IPython.testing import decorators as dec
 from IPython.testing import tools as tt
 
@@ -107,6 +113,49 b' class SubProcessTestCase(tt.TempFileMixin):'
         status = system('%s -c "import sys"' % python)
         self.assertEqual(status, 0)
 
+    def assert_interrupts(self, command):
+        """
+        Interrupt a subprocess after a second.
+        """
+        if threading.main_thread() != threading.current_thread():
+            raise nt.SkipTest("Can't run this test if not in main thread.")
+
+        # Some tests can overwrite SIGINT handler (by using pdb for example),
+        # which then breaks this test, so just make sure it's operating
+        # normally.
+        signal.signal(signal.SIGINT, signal.default_int_handler)
+
+        def interrupt():
+            # Wait for subprocess to start:
+            time.sleep(0.5)
+            interrupt_main()
+
+        threading.Thread(target=interrupt).start()
+        start = time.time()
+        try:
+            result = command()
+        except KeyboardInterrupt:
+            # Success!
+            pass
+        end = time.time()
+        self.assertTrue(
+            end - start < 2, "Process didn't die quickly: %s" % (end - start)
+        )
+        return result
+
+    def test_system_interrupt(self):
+        """
+        When interrupted in the way ipykernel interrupts IPython, the
+        subprocess is interrupted.
+        """
+        def command():
+            return system('%s -c "import time; time.sleep(5)"' % python)
+
+        status = self.assert_interrupts(command)
+        self.assertNotEqual(
+            status, 0, "The process wasn't interrupted. Status: %s" % (status,)
+        )
+
     def test_getoutput(self):
         out = getoutput('%s "%s"' % (python, self.fname))
         # we can't rely on the order the line buffered streams are flushed
@@ -131,7 +180,7 b' class SubProcessTestCase(tt.TempFileMixin):'
         out, err = getoutputerror('%s "%s"' % (python, self.fname))
         self.assertEqual(out, 'on stdout')
         self.assertEqual(err, 'on stderr')
-    
+
     def test_get_output_error_code(self):
         quiet_exit = '%s -c "import sys; sys.exit(1)"' % python
         out, err, code = get_output_error_code(quiet_exit)
@@ -142,3 +191,5 b' class SubProcessTestCase(tt.TempFileMixin):'
         self.assertEqual(out, 'on stdout')
         self.assertEqual(err, 'on stderr')
         self.assertEqual(code, 0)
+
+