Programmer needs to ensure that initializations happens before other
operations on gatomicrefcount as otherwise they could access
uninitialized memory, so there is no practical use case for making
initialization atomic.
Without gatomic.h, build fails on:
In file included from garcbox.c:24:0:
garcbox.c: In function ‘g_atomic_rc_box_acquire’:
grefcount.h:101:13: error: implicit declaration of function ‘g_atomic_int_get’; did you mean ‘__atomic_store’? [-Werror=implicit-function-declaration]
(void) (g_atomic_int_get (rc) == G_MAXINT ? 0 : g_atomic_int_inc ((rc))); \
^
garcbox.c:292:3: note: in expansion of macro ‘g_atomic_ref_count_inc’
g_atomic_ref_count_inc (&real_box->ref_count);
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
If we're using GCC we can use __extension__ to inline the grefcount and
gatomicrefcount API, and avoid the function call.
These macros are only enabled if G_DISABLE_CHECKS is defined, as they
remove critical warnings when the reference counters achieve saturation.
We have a common pattern for reference counting in GLib, but we always
implement it with ad hoc code. This is a good chance at trying to
standardise the implementation and make it public, so that other code
using GLib can take advantage of shared behaviour and semantics.
Instead of simply taking an integer variable, we should create type
aliases, to immediately distinguish the reference counting semantics of
the code; we can handle mixing atomic reference counting with a
non-atomic type (and vice versa) by using differently signed values for
the atomic and non-atomic cases.
The gatomicrefcount type is modelled on the Linux kernel refcount_t
type; the grefcount type is added to let single-threaded code bases to
avoid paying the price of atomic memory barriers on reference counting
operations.
