gst/: Yet another gratuitous GString micro-optimisation: add a (private) function that serialises a structure appendi...

Original commit message from CVS:
* gst/gst_private.h: (STRUCTURE_ESTIMATED_STRING_LEN):
* gst/gstcaps.c: (gst_caps_to_string):
* gst/gststructure.c: (GST_ASCII_IS_STRING),
(priv_gst_structure_append_to_gstring), (gst_structure_to_string):
Yet another gratuitous GString micro-optimisation: add a (private)
function that serialises a structure appending to an existing
GString, so that when we serialise caps we don't need to alloc+free
a throwaway GString for each structure (each of which also entailing
multiple reallocs on the way); also use g_string_sized_new() in
various places with an approximate string length to avoid reallocs
within GString. See #500143.

ChangeLog

@@ -1,3 +1,17 @@
+2008-01-09  Tim-Philipp Müller  <tim at centricular dot net>
+
+	* gst/gst_private.h: (STRUCTURE_ESTIMATED_STRING_LEN):
+	* gst/gstcaps.c: (gst_caps_to_string):
+	* gst/gststructure.c: (GST_ASCII_IS_STRING),
+	  (priv_gst_structure_append_to_gstring), (gst_structure_to_string):
+	  Yet another gratuitous GString micro-optimisation: add a (private)
+	  function that serialises a structure appending to an existing
+	  GString, so that when we serialise caps we don't need to alloc+free
+	  a throwaway GString for each structure (each of which also entailing
+	  multiple reallocs on the way); also use g_string_sized_new() in
+	  various places with an approximate string length to avoid reallocs
+	  within GString. See #500143.
+
 2008-01-09  Tim-Philipp Müller  <tim at centricular dot net>
 
 	* gst/gststructure.c: (gst_structure_id_set_value):

gst/gst_private.h

@@ -39,6 +39,7 @@ extern const char             g_log_domain_gstreamer[];
 
 /* Needed for GstRegistry * */
 #include "gstregistry.h"
+#include "gststructure.h"
 
 G_BEGIN_DECLS
 
@@ -65,6 +66,13 @@ void  _gst_value_initialize (void);
 gboolean _priv_gst_registry_remove_cache_plugins (GstRegistry *registry);
 void _priv_gst_registry_cleanup (void);
 
+/* used in both gststructure.c and gstcaps.c; numbers are completely made up */
+#define STRUCTURE_ESTIMATED_STRING_LEN(s) (16 + (s)->fields->len * 22)
+
+gboolean  priv_gst_structure_append_to_gstring (const GstStructure * structure,
+                                                GString            * s);
+
+
 /*** debugging categories *****************************************************/
 
 #ifndef GST_DISABLE_GST_DEBUG

gst/gstcaps.c

@@ -1773,7 +1773,7 @@ gst_caps_replace (GstCaps ** caps, GstCaps * newcaps)
 gchar *
 gst_caps_to_string (const GstCaps * caps)
 {
-  guint i;
+  guint i, slen;
   GString *s;
 
   /* NOTE:  This function is potentially called by the debug system,
@@ -1792,10 +1792,15 @@ gst_caps_to_string (const GstCaps * caps)
     return g_strdup ("EMPTY");
   }
 
-  s = g_string_new ("");
+  /* estimate a rough string length to avoid unnecessary reallocs in GString */
+  slen = 0;
+  for (i = 0; i < caps->structs->len; i++) {
+    slen += STRUCTURE_ESTIMATED_STRING_LEN (gst_caps_get_structure (caps, i));
+  }
+
+  s = g_string_sized_new (slen);
   for (i = 0; i < caps->structs->len; i++) {
     GstStructure *structure;
-    char *sstr;
 
     if (i > 0) {
       /* ';' is now added by gst_structure_to_string */
@@ -1803,15 +1808,12 @@ gst_caps_to_string (const GstCaps * caps)
     }
 
     structure = gst_caps_get_structure (caps, i);
-    sstr = gst_structure_to_string (structure);
-    g_string_append (s, sstr);
-    g_free (sstr);
+    priv_gst_structure_append_to_gstring (structure, s);
   }
   if (s->len && s->str[s->len - 1] == ';') {
     /* remove latest ';' */
     s->str[--s->len] = '\0';
   }
-
   return g_string_free (s, FALSE);
 }
 

gst/gststructure.c

@@ -1506,6 +1506,39 @@ gst_structure_value_get_generic_type (GValue * val)
       ((c) == '-') || ((c) == '+') || ((c) == '/') || ((c) == ':') || \
       ((c) == '.'))
 
+gboolean
+priv_gst_structure_append_to_gstring (const GstStructure * structure,
+    GString * s)
+{
+  GstStructureField *field;
+  guint i;
+
+  g_return_val_if_fail (s != NULL, FALSE);
+
+  g_string_append (s, g_quark_to_string (structure->name));
+  for (i = 0; i < structure->fields->len; i++) {
+    char *t;
+    GType type;
+
+    field = GST_STRUCTURE_FIELD (structure, i);
+
+    t = gst_value_serialize (&field->value);
+    type = gst_structure_value_get_generic_type (&field->value);
+
+    g_string_append_len (s, ", ", 2);
+    /* FIXME: do we need to escape fieldnames? */
+    g_string_append (s, g_quark_to_string (field->name));
+    g_string_append_len (s, "=(", 2);
+    g_string_append (s, gst_structure_to_abbr (type));
+    g_string_append_c (s, ')');
+    g_string_append (s, GST_STR_NULL (t));
+    g_free (t);
+  }
+
+  g_string_append_c (s, ';');
+  return TRUE;
+}
+
 /**
  * gst_structure_to_string:
  * @structure: a #GstStructure
@@ -1518,9 +1551,7 @@ gst_structure_value_get_generic_type (GValue * val)
 gchar *
 gst_structure_to_string (const GstStructure * structure)
 {
-  GstStructureField *field;
   GString *s;
-  guint i;
 
   /* NOTE:  This function is potentially called by the debug system,
    * so any calls to gst_log() (and GST_DEBUG(), GST_LOG(), etc.)
@@ -1530,25 +1561,10 @@ gst_structure_to_string (const GstStructure * structure)
 
   g_return_val_if_fail (structure != NULL, NULL);
 
-  s = g_string_new ("");
-  g_string_append_printf (s, "%s", g_quark_to_string (structure->name));
-  for (i = 0; i < structure->fields->len; i++) {
-    char *t;
-    GType type;
-
-    field = GST_STRUCTURE_FIELD (structure, i);
-
-    t = gst_value_serialize (&field->value);
-    type = gst_structure_value_get_generic_type (&field->value);
-
-    /* FIXME: do we need to escape fieldnames? */
-    g_string_append_printf (s, ", %s=(%s)%s", g_quark_to_string (field->name),
-        gst_structure_to_abbr (type), GST_STR_NULL (t));
-    g_free (t);
-  }
-
-  g_string_append_c (s, ';');
-
+  /* we estimate a minimum size based on the number of fields in order to
+   * avoid unnecessary reallocs within GString */
+  s = g_string_sized_new (STRUCTURE_ESTIMATED_STRING_LEN (structure));
+  priv_gst_structure_append_to_gstring (structure, s);
   return g_string_free (s, FALSE);
 }