Bug 4198

Created attachment 3002 [details] [review]
Treat a 0 reference count same as -1 in reference and destroy functions

This patch changes the common pattern of:

    if (object->ref_count == (unsigned int)-1)
	return;

that appears in all object_reference and corresponding object_destroy functions
to:

    if (object->ref_count <= 0)
	return;

This should catch and stop the 0 ref_count from changing. It also makes all
negative ref_count values equivalently no-ops, which I don't think should
hurt anything.

Created attachment 3009 [details] [review]
Crash by assert if ref_count == 0 in reference or destroy.

Owen pointed out that detecting this error and then silently doing nothing
is not helpful.

We can't use standard cairo error reporting since we're detecting garbage
objects
in these cases. So this patch just uses assert to crash if the user ever does
this.

It would probably be even better to print a helpful message to the user
in this case.

Created attachment 3010 [details] [review]
Fixed version (missing semicolon)

Same as previous patch, but this one actually compiles, (fixed missing
semicolon).

2005-08-23  Carl Worth  <cworth@cworth.org>

        Reviewed by: otaylor
        Fixes bug #4198

        * src/cairo-font.c: (cairo_font_face_reference),
        (cairo_font_face_destroy), (cairo_scaled_font_reference),
        (cairo_scaled_font_destroy):
        * src/cairo-pattern.c: (cairo_pattern_reference),
        (cairo_pattern_destroy):
        * src/cairo-surface.c: (cairo_surface_reference),
        (cairo_surface_destroy):
        * src/cairo.c: (cairo_reference), (cairo_destroy):
        Detect (by assert and crash) if users attempt to twice destroy or
        re-reference a destroyed object. The condition for detecting this
        case is a ref_count of 0.