[Spice-devel] [PATCH spice-gtk] Remove unnecessary debug check from SPICE_DEBUG

[Frediano Ziglio]

> 
> Calling spice_util_get_debug() from the SPICE_DEBUG() macro is
> unnecessary since g_log() will already check whether the message will
> actually be printed. The only benefit to calling this function from
> SPICE_DEBUG() is that it ensures that the SPICE_DEBUG environment
> variable gets read the very first time we try to log something with
> this macro. To solve this problem we instead use a constructor function
> to ensure that the env var is read at startup.
> 
> Signed-off-by: Jonathon Jongsma <jjongsma at redhat.com>
> ---
>  src/spice-util.c | 17 ++++++++++-------
>  src/spice-util.h |  7 ++-----
>  2 files changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/src/spice-util.c b/src/spice-util.c
> index 86377b6..848f20a 100644
> --- a/src/spice-util.c
> +++ b/src/spice-util.c
> @@ -18,6 +18,7 @@
>  */
>  #include "config.h"
>  
> +#include <common/macros.h>
>  #include <stdbool.h>
>  #include <stdlib.h>
>  #include <string.h>

I would prefer the include after system includes, like spice-server rules.

> @@ -63,13 +64,6 @@ static void spice_util_enable_debug_messages(void)
>   **/
>  void spice_util_set_debug(gboolean enabled)
>  {
> -    /* Make sure debug_once has been initialised
> -     * with the value of SPICE_DEBUG already, otherwise
> -     * spice_util_get_debug() may overwrite the value
> -     * that was just set using spice_util_set_debug()
> -     */
> -    spice_util_get_debug();
> -
>      if (enabled) {
>          spice_util_enable_debug_messages();
>      }
> @@ -88,6 +82,15 @@ static gpointer getenv_debug(gpointer data)
>      return GINT_TO_POINTER(debug);
>  }
>  
> +/* Make sure debug_once has been initialised with the value of SPICE_DEBUG
> at
> + * startup, otherwise spice_util_get_debug() may overwrite the value that is
> + * set using spice_util_set_debug() */
> +SPICE_CONSTRUCTOR_FUNC(spice_log_init)
> +{
> +    /* ensure that we enable debugging if the SPICE_DEBUG variable is set */
> +    spice_util_get_debug();
> +}
> +
>  gboolean spice_util_get_debug(void)
>  {
>      g_once(&debug_once, getenv_debug, NULL);

the g_once/GOnce is redundant with constructors. Constructors are
called in a single thread environment so don't need any serialization
(note: destructors don't follow this rule).
You could then use a simpler variable and write all SPICE_DEBUG check
in the constructor.
At this point you could use the new variable instead of
spice_util_get_debug (maybe using a static inline function to keep
API/flexibility).

> diff --git a/src/spice-util.h b/src/spice-util.h
> index a2a7683..7a95a9e 100644
> --- a/src/spice-util.h
> +++ b/src/spice-util.h
> @@ -32,11 +32,8 @@ gulong spice_g_signal_connect_object(gpointer instance,
>                                       GConnectFlags connect_flags);
>  gchar* spice_uuid_to_string(const guint8 uuid[16]);
>  
> -#define SPICE_DEBUG(fmt, ...)                                   \
> -    do {                                                        \
> -        if (G_UNLIKELY(spice_util_get_debug()))                 \
> -            g_debug(G_STRLOC " " fmt, ## __VA_ARGS__);          \
> -    } while (0)
> +#define SPICE_DEBUG(fmt, ...) \
> +    g_debug(G_STRLOC " " fmt, ## __VA_ARGS__)
>  
>  #define SPICE_RESERVED_PADDING (10 * sizeof(void*))
>  

I think the unlikely here is an optimization we want avoiding the
expensive g_debug call. And would be even better with my variable
proposal.

Frediano