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basic: replace __sync intrinsics with __atomic

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Commented reasoning on why it's safe to replace
__sync_bool_compare_and_swap with __atomic_compare_exchange_n in each
location even though the latter has an additional side effect.

__sync_synchronize should be equivalent to __atomic_thread_fence with
__ATOMIC_SEQ_CST memory ordering.
This commit is contained in:
matoro
2022-07-14 17:34:15 -04:00
parent 9ddb63f5cf
commit 5ba4295bea
1 changed files with 21 additions and 9 deletions
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src/basic/sigbus.c
+21 -9
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@@ -28,24 +28,31 @@ static void sigbus_push(void *addr) {
assert(addr);
/* Find a free place, increase the number of entries and leave, if we can */
for (size_t u = 0; u < SIGBUS_QUEUE_MAX; u++)
if (__sync_bool_compare_and_swap(&sigbus_queue[u], NULL, addr)) {
__sync_fetch_and_add(&n_sigbus_queue, 1);
for (size_t u = 0; u < SIGBUS_QUEUE_MAX; u++) {
/* OK to initialize this here since we haven't started the atomic ops yet */
void *tmp = NULL;
if (__atomic_compare_exchange_n(&sigbus_queue[u], &tmp, addr, false,
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) {
__atomic_fetch_add(&n_sigbus_queue, 1, __ATOMIC_SEQ_CST);
return;
}
}
/* If we can't, make sure the queue size is out of bounds, to
* mark it as overflow */
for (;;) {
unsigned c;
sig_atomic_t c;
__sync_synchronize();
__atomic_thread_fence(__ATOMIC_SEQ_CST);
c = n_sigbus_queue;
if (c > SIGBUS_QUEUE_MAX) /* already overflow */
return;
if (__sync_bool_compare_and_swap(&n_sigbus_queue, c, c + SIGBUS_QUEUE_MAX))
/* OK if we clobber c here, since we either immediately return
* or it will be immediately reinitialized on next loop */
if (__atomic_compare_exchange_n(&n_sigbus_queue, &c, c + SIGBUS_QUEUE_MAX, false,
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST))
return;
}
}
@@ -56,7 +63,7 @@ int sigbus_pop(void **ret) {
for (;;) {
unsigned u, c;
__sync_synchronize();
__atomic_thread_fence(__ATOMIC_SEQ_CST);
c = n_sigbus_queue;
if (_likely_(c == 0))
@@ -72,8 +79,13 @@ int sigbus_pop(void **ret) {
if (!addr)
continue;
if (__sync_bool_compare_and_swap(&sigbus_queue[u], addr, NULL)) {
__sync_fetch_and_sub(&n_sigbus_queue, 1);
/* OK if we clobber addr here, since we either immediately return
* or it will be immediately reinitialized on next loop */
if (__atomic_compare_exchange_n(&sigbus_queue[u], &addr, NULL, false,
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) {
__atomic_fetch_sub(&n_sigbus_queue, 1, __ATOMIC_SEQ_CST);
/* If we successfully entered this if condition, addr won't
* have been modified since its assignment, so safe to use it */
*ret = addr;
return 1;
}