bpo-34563: Fix for invalid assert on big output of multiprocessing.Process

Lib/test/test_multiprocessing_with_big_output.py

@@ -0,0 +1,25 @@
+import unittest
+from multiprocessing.pool import Pool
+from time import sleep
+
+
+def func():
+    return 'test' * (10 ** 9)
+
+
+class TestMultiprocessingWithBigOutput(unittest.TestCase):
+    @unittest.skip("skipping test for manual use only. Highly demanding on RAM and time consuming")
+    def test_big_subprocess_output(self):
+        with Pool() as pool:
+            task = pool.apply_async(func)
+            for i in range(10):
+                if task.ready():
+                    task.get()
+                    break
+                sleep(30)
+            else:
+                self.fail('test_big_subprocess_output() timeout.')
+
+
+if __name__ == '__main__':
+    unittest.main()

Misc/NEWS.d/next/Library/2018-09-01-20-43-10.bpo-34563.7NQK7B.rst

@@ -0,0 +1 @@
+Fix for invalid assert on big output of multiprocessing.Process

Modules/_winapi.c

@@ -1338,7 +1338,7 @@ _winapi_PeekNamedPipe_impl(PyObject *module, HANDLE handle, int size)
         }
         if (_PyBytes_Resize(&buf, nread))
             return NULL;
-        return Py_BuildValue("Nii", buf, navail, nleft);
+        return Py_BuildValue("NII", buf, navail, nleft);
     }
     else {
         Py_BEGIN_ALLOW_THREADS
@@ -1347,15 +1347,15 @@ _winapi_PeekNamedPipe_impl(PyObject *module, HANDLE handle, int size)
         if (!ret) {
             return PyErr_SetExcFromWindowsErr(PyExc_OSError, 0);
         }
-        return Py_BuildValue("ii", navail, nleft);
+        return Py_BuildValue("II", navail, nleft);
     }
 }
 
 /*[clinic input]
 _winapi.ReadFile
 
     handle: HANDLE
-    size: int
+    size: DWORD
     overlapped as use_overlapped: bool(accept={int}) = False
 [clinic start generated code]*/