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Simplify `sos_alloc()' implementation

Instead of maintaining a pointer to the `sos_memory' array, maintain an
index that tells the next free position. When atomic operations are
available, the allocation boils down to a single fetch-and-add
operation.
This commit is contained in:
Tommi Rantala 2012-09-19 14:00:20 +03:00
parent 26fc1563fb
commit 9a3565ddc1
3 changed files with 30 additions and 28 deletions

View file

@ -110,11 +110,12 @@ cmpxchg_ptr (void *addr, void *old, void *new)
return AO_compare_and_swap(u.aop, (AO_t) old, (AO_t) new);
}
# define fetch_and_add1(_ptr) AO_fetch_and_add1(_ptr)
# define fetch_and_add(_ptr, value) AO_fetch_and_add(_ptr, value)
/* GCC 3.2.0 on HP-UX crashes on cmpxchg_ptr() */
# if !(defined(__hpux) && __GNUC__ == 3 && __GNUC_MINOR__ == 2)
# define HAVE_CMPXCHG
# endif
# define HAVE_FETCH_AND_ADD1
# define HAVE_FETCH_AND_ADD
#else
# ifdef HAVE_IA64INTRIN_H
# include <ia64intrin.h>
@ -132,8 +133,9 @@ cmpxchg_ptr (void *addr, void *old, void *new)
return __sync_bool_compare_and_swap(u.vlp, (long) old, (long) new);
}
# define fetch_and_add1(_ptr) __sync_fetch_and_add(_ptr, 1)
# define fetch_and_add(_ptr, value) __sync_fetch_and_add(_ptr, value)
# define HAVE_CMPXCHG
# define HAVE_FETCH_AND_ADD1
# define HAVE_FETCH_AND_ADD
# endif
#endif
#define atomic_read(ptr) (*(ptr))

View file

@ -50,7 +50,7 @@ unw_flush_cache (unw_addr_space_t as, unw_word_t lo, unw_word_t hi)
unw_flush_cache() is allowed to flush more than the requested
range. */
#ifdef HAVE_FETCH_AND_ADD1
#ifdef HAVE_FETCH_AND_ADD
fetch_and_add1 (&as->cache_generation);
#else
# warning unw_flush_cache(): need a way to atomically increment an integer.

View file

@ -40,48 +40,48 @@ WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */
#endif
static char sos_memory[SOS_MEMORY_SIZE] ALIGNED(MAX_ALIGN);
static char *sos_memp;
static size_t sos_memory_freepos;
static size_t pg_size;
HIDDEN void *
sos_alloc (size_t size)
{
char *mem;
#ifdef HAVE_CMPXCHG
char *old_mem;
size_t pos;
size = UNW_ALIGN(size, MAX_ALIGN);
if (!sos_memp)
cmpxchg_ptr (&sos_memp, 0, sos_memory);
do
{
old_mem = sos_memp;
mem = (char *) UNW_ALIGN((unsigned long) old_mem, MAX_ALIGN);
mem += size;
assert (mem < sos_memory + sizeof (sos_memory));
}
while (!cmpxchg_ptr (&sos_memp, old_mem, mem));
#if defined(__GNUC__)
/* Assume `sos_memory' is suitably aligned. */
assert(((uintptr_t) &sos_memory[0] & (MAX_ALIGN-1)) == 0);
#endif
#if defined(__GNUC__) && defined(HAVE_FETCH_AND_ADD)
pos = fetch_and_add (&sos_memory_freepos, size);
#else
static define_lock (sos_lock);
intrmask_t saved_mask;
size = UNW_ALIGN(size, MAX_ALIGN);
lock_acquire (&sos_lock, saved_mask);
{
if (!sos_memp)
sos_memp = sos_memory;
mem = (char *) UNW_ALIGN((unsigned long) sos_memp, MAX_ALIGN);
mem += size;
assert (mem < sos_memory + sizeof (sos_memory));
sos_memp = mem;
# ifndef __GNUC__
/* No assumptions about `sos_memory' alignment. */
if (sos_memory_freepos == 0)
{
unsigned align = UNW_ALIGN((uintptr_t) &sos_memory[0], MAX_ALIGN)
- (uintptr_t) &sos_memory[0];
sos_memory_freepos = align;
}
# endif
pos = sos_memory_freepos;
sos_memory_freepos += size;
}
lock_release (&sos_lock, saved_mask);
#endif
return mem;
assert (((uintptr_t) &sos_memory[pos] & (MAX_ALIGN-1)) == 0);
assert ((pos+size) <= SOS_MEMORY_SIZE);
return &sos_memory[pos];
}
/* Must be called while holding the mempool lock. */