Libguestfs - Jan 2018 - [nbdkit PATCH] errors: Use lighter-weight locking

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@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

On Thu, Jan 25, 2018 at 09:32:49AM -0600, Eric Blake
wrote:
> 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@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. */
> -- 
ACK.  Maybe even inline those functions?

Rich.

-- 
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