give priority to progress messages

In theory it is possible for sideband channel #2 to be delayed if
pack data is quick to come up for sideband channel #1.  And because
data for channel #2 is read only 128 bytes at a time while pack data
is read 8192 bytes at a time, it is possible for many pack blocks to
be sent to the client before the progress message fifo is emptied,
making the situation even worse.  This would result in totally garbled
progress display on the client's console as local progress gets mixed
with partial remote progress lines.

Let's prevent such situations by giving transmission priority to
progress messages over pack data at all times.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-upload-archive.c

@@ -132,7 +132,6 @@ int cmd_upload_archive(int argc, const char **argv, const char *prefix)
 
 	while (1) {
 		struct pollfd pfd[2];
-		ssize_t processed[2] = { 0, 0 };
 		int status;
 
 		pfd[0].fd = fd1[0];
@@ -147,15 +146,14 @@ int cmd_upload_archive(int argc, const char **argv, const char *prefix)
 			}
 			continue;
 		}
-		if (pfd[0].revents & POLLIN)
-			/* Data stream ready */
-			processed[0] = process_input(pfd[0].fd, 1);
 		if (pfd[1].revents & POLLIN)
 			/* Status stream ready */
-			processed[1] = process_input(pfd[1].fd, 2);
-		/* Always finish to read data when available */
-		if (processed[0] || processed[1])
-			continue;
+			if (process_input(pfd[1].fd, 2))
+				continue;
+		if (pfd[0].revents & POLLIN)
+			/* Data stream ready */
+			if (process_input(pfd[0].fd, 1))
+				continue;
 
 		if (waitpid(writer, &status, 0) < 0)
 			error_clnt("%s", lostchild);

upload-pack.c

@@ -218,6 +218,23 @@ static void create_pack_file(void)
 			}
 			continue;
 		}
+		if (0 <= pe && (pfd[pe].revents & (POLLIN|POLLHUP))) {
+			/* Status ready; we ship that in the side-band
+			 * or dump to the standard error.
+			 */
+			sz = xread(pack_objects.err, progress,
+				  sizeof(progress));
+			if (0 < sz)
+				send_client_data(2, progress, sz);
+			else if (sz == 0) {
+				close(pack_objects.err);
+				pack_objects.err = -1;
+			}
+			else
+				goto fail;
+			/* give priority to status messages */
+			continue;
+		}
 		if (0 <= pu && (pfd[pu].revents & (POLLIN|POLLHUP))) {
 			/* Data ready; we keep the last byte to ourselves
 			 * in case we detect broken rev-list, so that we
@@ -255,21 +272,6 @@ static void create_pack_file(void)
 			if (sz < 0)
 				goto fail;
 		}
-		if (0 <= pe && (pfd[pe].revents & (POLLIN|POLLHUP))) {
-			/* Status ready; we ship that in the side-band
-			 * or dump to the standard error.
-			 */
-			sz = xread(pack_objects.err, progress,
-				  sizeof(progress));
-			if (0 < sz)
-				send_client_data(2, progress, sz);
-			else if (sz == 0) {
-				close(pack_objects.err);
-				pack_objects.err = -1;
-			}
-			else
-				goto fail;
-		}
 	}
 
 	if (finish_command(&pack_objects)) {