From 247b71e690708a529cf639e196815cbbbee077d7 Mon Sep 17 00:00:00 2001
From: Paul Smith <psmith@gnu.org>
Date: Sun, 13 Mar 2016 15:59:12 -0400
Subject: [PATCH] * main.c(main): Disable output sync without parallel builds.

---
 main.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/main.c b/main.c
index 62ed7a8a..22af6011 100644
--- a/main.c
+++ b/main.c
@@ -1464,13 +1464,6 @@ main (int argc, char **argv, char **envp)
 
   decode_env_switches (STRING_SIZE_TUPLE ("MAKEFLAGS"));
 
-  /* In output sync mode we need to sync any output generated by reading the
-     makefiles, such as in $(info ...) or stderr from $(shell ...) etc.  */
-
-  syncing = make_sync.syncout = (output_sync == OUTPUT_SYNC_LINE
-                                 || output_sync == OUTPUT_SYNC_TARGET);
-  OUTPUT_SET (&make_sync);
-
 #if 0
   /* People write things like:
         MFLAGS="CC=gcc -pipe" "CFLAGS=-g"
@@ -1478,6 +1471,13 @@ main (int argc, char **argv, char **envp)
   decode_env_switches (STRING_SIZE_TUPLE ("MFLAGS"));
 #endif
 
+  /* In output sync mode we need to sync any output generated by reading the
+     makefiles, such as in $(info ...) or stderr from $(shell ...) etc.  */
+
+  syncing = make_sync.syncout = (output_sync == OUTPUT_SYNC_LINE
+                                 || output_sync == OUTPUT_SYNC_TARGET);
+  OUTPUT_SET (&make_sync);
+
   decode_switches (argc, (const char **)argv, 0);
 
     /* Set a variable specifying whether stdout/stdin is hooked to a TTY.  */
@@ -2053,6 +2053,17 @@ main (int argc, char **argv, char **envp)
     }
 #endif
 
+  /* If we're not using parallel jobs, then we don't need output sync.
+     This is so people can enable output sync in GNUMAKEFLAGS or similar, but
+     not have it take effect unless parallel builds are enabled.  */
+  if (syncing && job_slots == 1)
+    {
+      OUTPUT_UNSET ();
+      output_close (&make_sync);
+      syncing = 0;
+      output_sync = OUTPUT_SYNC_NONE;
+    }
+
 #ifndef MAKE_SYMLINKS
   if (check_symlink_flag)
     {