On 9 Jun 2017, at 17:47, Frediano Ziglio <fziglio@xxxxxxxxxx> wrote:
On Fri, 2017-06-09 at 05:47 -0400, Frediano Ziglio wrote:
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@xxxxxxxxxx>
---
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).
Right.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.
Hmm. This seems like unnecessary optimization to me. The glib logging
functions already have a check to see whether the message should be
printed. So adding our own (possibly out-of-sync) check around the call
seems unnecessary. Essentially:
if (spice_debug_enabled) {
// function call to g_logv() which contains pseudo-code like:
if (glib_debug_enabled) {
// log the message
}
}
I think if the debug function call overhead really is expensive enough
that it starts affecting the behavior of the program, then enabling
logging we will *definitely* affect the behavior of the program. I'd
rather to see evidence that it's a problem before we optimize it.
Jonathon
Yes, but you are removing an optimization without evidence too.
The change was introduced by f7daf5a4987af3fc8f8a15d1e1655995ff610009:
commit f7daf5a4987af3fc8f8a15d1e1655995ff610009
Author: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>
Date: Wed Nov 17 22:14:15 2010 +0100
gtk: add a flag to turn debug off, SPICE_DEBUG=1 to override
No rationale or explanation precisely if the G_UNLIKELY optimization
was intentional.About intentional or not, why this:#define spice_warn_if_fail(x) G_STMT_START { \if G_LIKELY(x) { } else { \spice_warning("condition `%s' failed", #x); \} \} G_STMT_ENDinstead of G_UNLIKELY(!(x)) ?
I think the code came from GLib headers (see glib/gmessages.h).
Maybe initially only G_LIKELY was available.
Or maybe the G_STMT_START was not used and they wanted to avoid
somebody put an else after the code (but the do {} while(0) trick is really
old...).
I see nothing “bad” in that code, it just looks weird.
Frediano
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