[Libguestfs] [nbdkit PATCH] errors: Use lighter-weight locking

[Eric Blake]

Commit d02d9c9d used pthread_mutex to avoid interleaving output.
However, the standard provides flockfile() for grouping related
FILE* I/O that must not be interleaved; and that may be
lighter-weight than rolling our own locking.

Signed-off-by: Eric Blake <eblake at redhat.com>
---

Pushing this one; as a related conversation on another mailing list
reminded me about flockfile().

 src/errors.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/src/errors.c b/src/errors.c
index c1efae6..471e3ea 100644
--- a/src/errors.c
+++ b/src/errors.c
@@ -1,5 +1,5 @@
 /* nbdkit
- * Copyright (C) 2013-2017 Red Hat Inc.
+ * Copyright (C) 2013-2018 Red Hat Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -44,21 +44,16 @@
 #include "nbdkit-plugin.h"
 #include "internal.h"

-/* Used to group piecemeal message construction into atomic output. */
-static pthread_mutex_t errors_lock = PTHREAD_MUTEX_INITIALIZER;
-
 static void
 lock (void)
 {
-  int r = pthread_mutex_lock (&errors_lock);
-  assert (!r);
+  flockfile (stderr);
 }

 static void
 unlock (void)
 {
-  int r = pthread_mutex_unlock (&errors_lock);
-  assert (!r);
+  funlockfile (stderr);
 }

 /* Called with lock taken. */
-- 
2.14.3