scaled-font: Update documentation and code with atomic refcounting

The documentation incorrectly states that
cairo_scaled_font_reference() locks a mutex. This is not true anymore
because refcounting is now done using atomics.

For the same reason, it is now possible to reference the scaled font,
instead of manually increasing its reference count, assuming that the
reference function accepts inputs with no references.

2 files changed, 12 insertions, 19 deletions

diff --git a/src/cairo-scaled-font-private.h b/src/cairo-scaled-font-private.h
index 029377b17..5c0ba3c13 100644
--- a/src/cairo-scaled-font-private.h
+++ b/src/cairo-scaled-font-private.h
@@ -64,11 +64,7 @@ struct _cairo_scaled_font {
      * the locks protecting them are as follows:
      *
      * 1. The reference count (scaled_font->ref_count)
-     *
-     *    Modifications to the reference count are protected by the
-     *    _cairo_scaled_font_map_mutex. This is because the reference
-     *    count of a scaled font is intimately related with the font
-     *    map itself, (and the magic holdovers array).
+     *    Modifications to the reference count are atomic.
      *
      * 2. The cache of glyphs (scaled_font->glyphs)
      * 3. The backend private data (scaled_font->surface_backend,
diff --git a/src/cairo-scaled-font.c b/src/cairo-scaled-font.c
index cb59bce67..3eb84eb7d 100644
--- a/src/cairo-scaled-font.c
+++ b/src/cairo-scaled-font.c
@@ -925,11 +925,9 @@ cairo_scaled_font_create (cairo_font_face_t          *font_face,
 	assert (! scaled_font->placeholder);
 
 	if (likely (scaled_font->status == CAIRO_STATUS_SUCCESS)) {
-	    /* We increment the reference count manually here, (rather
-	     * than calling into cairo_scaled_font_reference), since we
-	     * must modify the reference count while our lock is still
-	     * held. */
-	    _cairo_reference_count_inc (&scaled_font->ref_count);
+	    /* We must modify the reference count while our lock is
+	     * still held. */
+	    cairo_scaled_font_reference (scaled_font);
 	    _cairo_scaled_font_map_unlock ();
 	    return scaled_font;
 	}
@@ -1012,17 +1010,14 @@ cairo_scaled_font_create (cairo_font_face_t          *font_face,
 	    }
 
 	    if (likely (scaled_font->status == CAIRO_STATUS_SUCCESS)) {
-		/* We increment the reference count manually here, (rather
-		 * than calling into cairo_scaled_font_reference), since we
-		 * must modify the reference count while our lock is still
-		 * held. */
-
+		/* We must modify the reference count while our lock
+		 * is still held. */
 		old = font_map->mru_scaled_font;
 		font_map->mru_scaled_font = scaled_font;
 		/* increment reference count for the mru cache */
-		_cairo_reference_count_inc (&scaled_font->ref_count);
+		cairo_scaled_font_reference (scaled_font);
 		/* and increment for the returned reference */
-		_cairo_reference_count_inc (&scaled_font->ref_count);
+		cairo_scaled_font_reference (scaled_font);
 		_cairo_scaled_font_map_unlock ();
 
 		cairo_scaled_font_destroy (old);
@@ -1080,7 +1075,7 @@ cairo_scaled_font_create (cairo_font_face_t          *font_face,
     if (likely (status == CAIRO_STATUS_SUCCESS)) {
 	old = font_map->mru_scaled_font;
 	font_map->mru_scaled_font = scaled_font;
-	_cairo_reference_count_inc (&scaled_font->ref_count);
+	cairo_scaled_font_reference (scaled_font);
     }
 
     _cairo_scaled_font_map_unlock ();
@@ -1181,7 +1176,9 @@ cairo_scaled_font_reference (cairo_scaled_font_t *scaled_font)
 	    CAIRO_REFERENCE_COUNT_IS_INVALID (&scaled_font->ref_count))
 	return scaled_font;
 
-    assert (CAIRO_REFERENCE_COUNT_HAS_REFERENCE (&scaled_font->ref_count));
+    /* We would normally assert that we have a reference here but we
+     * can't get away with that because holdover scaled fonts have no
+     * references. */
 
     _cairo_reference_count_inc (&scaled_font->ref_count);