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There are only two types of systems we care about: Windows, and
variations of pthreads. Other systems can be dealt with by people who
care about them.
Windows
-------
On Windows, mutexes cannot be initialized statically, but on the other
hand, we are guaranteed to have atomic primitives available without a
mutex. This means mutexes can be initialized dynamically with
something like this:
#define PIXMAN_DEFINE_LOCK(name) \
static CRITICAL_SECTION __ ## name ## _critical_section; \
static CRITICAL_SECTION *__ ## name ## _ptr;
#define PIXMAN_LOCK(name) \
if (!PIXMAN_ATOMIC_POINTER_GET ((void **)&__ ## name ## _ptr)) \
{ \
_pixman_win32_initialize_critical_section ( \
&__ ## name ## _ptr, \
&__ ## name ## _critical_section); \
} \
\
EnterCriticalSection(&__ ## name ## _critical_section);
#define PIXMAN_UNLOCK(name) \
LeaveCriticalSection(&__ ## name ## _critical_section);
Where _pixman_win32_initialize_critical_section() would be responsible
for initializing the variables. (And not doing anything if they are
already set).
Pthreads
--------
On pthreads, we may or may not have atomic primitives, but mutexes can
always be initialized statically. That means we can fake atomic
primitives with mutexes if necessary.
Ie,. something like
#define PIXMAN_DEFINE_LOCK(name) \
pthread_mutex_t __ ## name ## __lock = pthread_mutex_initializer;
#ifdef BUILTIN_ATOMICS
...
#else
/* fake atomic primitives with mutexes */
#endif
Therefore, we can guarantee availability of the following macros:
PIXMAN_ATOMIC_POINTER_GET(void **)
PIXMAN_ATOMIC_POINTER_SET(void **, void *value)
PIXMAN_ATOMIC_POINTER_CMPXCHG()
PIXMAN_ATOMIC_INT_GET(atomic *a)
PIXMAN_ATOMIC_INT_SET(atomic *a, int value)
PIXMAN_ATOMIC_INT_DEC_AND_TEST(atomic *a)
PIXMAN_ATOMIC_INT_CMPXCHG(atomic, ...)
PIXMAN_MUTEX_DEFINE_STATIC(name)
PIXMAN_MUTEX_LOCK(name)
PIXMAN_MUTEX_UNLOCK(name)
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