Set O_APPEND mode for stdout/stderr and output-sync temporary files.

POSIX does not guarantee that writes will be atomic if a file is
opened for normal (non-append) output.  That means if multiple processes
are writing to the same file, output could be lost.  I can't think of
a real use-case where we would NOT want append for stdout/stderr, so
force it if we can.

1 files changed, 6 insertions, 0 deletions

diff --git a/main.c b/main.c
index fe8d355..83a95db 100644
--- a/main.c
+++ b/main.c
@@ -1195,6 +1195,12 @@ main (int argc, char **argv, char **envp)
   setlinebuf (stdout);
 #endif  /* setlinebuf missing.  */
 
+  /* Configure stdout/stderr to be in append mode.
+     This keeps parallel jobs from losing output due to overlapping writes.  */
+
+  set_append_mode (fileno (stdout));
+  set_append_mode (fileno (stderr));
+
   /* Figure out where this program lives.  */
 
   if (argv[0] == 0)