Issue 5619: Pass MS CRT debug flags into subprocesses

Misc/ACKS

@@ -685,6 +685,7 @@ Daniel Stutzbach
 Nathan Sullivan
 Mark Summerfield
 Hisao Suzuki
+Andrew Svetlov
 Kalle Svensson
 Paul Swartz
 Thenault Sylvain

Misc/NEWS

@@ -199,6 +199,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #5619: Multiprocessing children disobey the debug flag and causes
+  popups on windows buildbots. Patch applied to work around this issue.
+
 - Issue #5632: Thread.ident was None for the main thread and threads not created
   with the threading module.
 

Modules/_multiprocessing/win32_functions.c

@@ -130,6 +130,12 @@ win32_ExitProcess(PyObject *self, PyObject *args)
 	if (!PyArg_ParseTuple(args, "I", &uExitCode))
 		return NULL;
 
+	#if defined(Py_DEBUG)
+		SetErrorMode(SEM_FAILCRITICALERRORS|SEM_NOALIGNMENTFAULTEXCEPT|SEM_NOGPFAULTERRORBOX|SEM_NOOPENFILEERRORBOX);
+		_CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_DEBUG);
+	#endif
+
+
 	ExitProcess(uExitCode);
 
 	return NULL;

Python/pythonrun.c

@@ -1634,6 +1634,8 @@ void
 Py_FatalError(const char *msg)
 {
 	fprintf(stderr, "Fatal Python error: %s\n", msg);
+	fflush(stderr); /* it helps in Windows debug build */
+
 #ifdef MS_WINDOWS
 	{
 		size_t len = strlen(msg);