Issue 3551: Raise ValueError if the size causes ERROR_NO_SYSTEM_RESOURCES

Doc/library/multiprocessing.rst

@@ -710,7 +710,8 @@ Connection objects usually created using :func:`Pipe` -- see also
       Send an object to the other end of the connection which should be read
       using :meth:`recv`.
 
-      The object must be picklable.
+      The object must be picklable.  Very large pickles (approximately 32 MB+,
+      though it depends on the OS) may raise a ValueError exception.
 
    .. method:: recv()
 
@@ -742,7 +743,9 @@ Connection objects usually created using :func:`Pipe` -- see also
       complete message.
 
       If *offset* is given then data is read from that position in *buffer*.  If
-      *size* is given then that many bytes will be read from buffer.
+      *size* is given then that many bytes will be read from buffer.  Very large
+      buffers (approximately 32 MB+, though it depends on the OS) may raise a
+      ValueError exception
 
    .. method:: recv_bytes([maxlength])
 

Misc/NEWS

@@ -202,6 +202,10 @@ Core and Builtins
 Library
 -------
 
+- Issue 3551: Patch multiprocessing to raise a proper exception if the size of the
+  object when writefile is called causes a ERROR_NO_SYSTEM_RESOURCES. Added docs
+  to note the limitation
+
 - unittest.assertNotEqual() now uses the inequality operator (!=) instead 
   of the equality operator.
   

Modules/_multiprocessing/connection.h

@@ -131,8 +131,12 @@ connection_sendbytes(ConnectionObject *self, PyObject *args)
 
 	res = conn_send_string(self, buffer + offset, size);
 
-	if (res < 0)
-		return mp_SetError(PyExc_IOError, res);
+	if (res < 0) {
+		if (PyErr_Occurred())
+			return NULL;
+		else
+			return mp_SetError(PyExc_IOError, res);
+	}
 
 	Py_RETURN_NONE;
 }

Modules/_multiprocessing/pipe_connection.c

@@ -23,6 +23,12 @@ conn_send_string(ConnectionObject *conn, char *string, size_t length)
 	Py_BEGIN_ALLOW_THREADS
 	ret = WriteFile(conn->handle, string, length, &amount_written, NULL);
 	Py_END_ALLOW_THREADS
+
+	if (ret == 0 && GetLastError() == ERROR_NO_SYSTEM_RESOURCES) {
+		PyErr_Format(PyExc_ValueError, "Cannnot send %" PY_FORMAT_SIZE_T "d bytes over connection", length);
+		return MP_STANDARD_ERROR;
+	}
+
 	return ret ? MP_SUCCESS : MP_STANDARD_ERROR;
 }