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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); 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_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() */ /* GCC 3.2.0 on HP-UX crashes on cmpxchg_ptr() */
# if !(defined(__hpux) && __GNUC__ == 3 && __GNUC_MINOR__ == 2) # if !(defined(__hpux) && __GNUC__ == 3 && __GNUC_MINOR__ == 2)
# define HAVE_CMPXCHG # define HAVE_CMPXCHG
# endif # endif
# define HAVE_FETCH_AND_ADD1 # define HAVE_FETCH_AND_ADD
#else #else
# ifdef HAVE_IA64INTRIN_H # ifdef HAVE_IA64INTRIN_H
# include <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); 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_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_CMPXCHG
# define HAVE_FETCH_AND_ADD1 # define HAVE_FETCH_AND_ADD
# endif # endif
#endif #endif
#define atomic_read(ptr) (*(ptr)) #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 unw_flush_cache() is allowed to flush more than the requested
range. */ range. */
#ifdef HAVE_FETCH_AND_ADD1 #ifdef HAVE_FETCH_AND_ADD
fetch_and_add1 (&as->cache_generation); fetch_and_add1 (&as->cache_generation);
#else #else
# warning unw_flush_cache(): need a way to atomically increment an integer. # 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 #endif
static char sos_memory[SOS_MEMORY_SIZE] ALIGNED(MAX_ALIGN); 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; static size_t pg_size;
HIDDEN void * HIDDEN void *
sos_alloc (size_t size) sos_alloc (size_t size)
{ {
char *mem; size_t pos;
#ifdef HAVE_CMPXCHG
char *old_mem;
size = UNW_ALIGN(size, MAX_ALIGN); 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); #if defined(__GNUC__)
mem += size; /* Assume `sos_memory' is suitably aligned. */
assert (mem < sos_memory + sizeof (sos_memory)); assert(((uintptr_t) &sos_memory[0] & (MAX_ALIGN-1)) == 0);
} #endif
while (!cmpxchg_ptr (&sos_memp, old_mem, mem));
#if defined(__GNUC__) && defined(HAVE_FETCH_AND_ADD)
pos = fetch_and_add (&sos_memory_freepos, size);
#else #else
static define_lock (sos_lock); static define_lock (sos_lock);
intrmask_t saved_mask; intrmask_t saved_mask;
size = UNW_ALIGN(size, MAX_ALIGN);
lock_acquire (&sos_lock, saved_mask); lock_acquire (&sos_lock, saved_mask);
{ {
if (!sos_memp) # ifndef __GNUC__
sos_memp = sos_memory; /* No assumptions about `sos_memory' alignment. */
if (sos_memory_freepos == 0)
mem = (char *) UNW_ALIGN((unsigned long) sos_memp, MAX_ALIGN); {
mem += size; unsigned align = UNW_ALIGN((uintptr_t) &sos_memory[0], MAX_ALIGN)
assert (mem < sos_memory + sizeof (sos_memory)); - (uintptr_t) &sos_memory[0];
sos_memp = mem; sos_memory_freepos = align;
}
# endif
pos = sos_memory_freepos;
sos_memory_freepos += size;
} }
lock_release (&sos_lock, saved_mask); lock_release (&sos_lock, saved_mask);
#endif #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. */ /* Must be called while holding the mempool lock. */