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feat: P2-3 repl_wait_ack() with pthread_cond_timedwait + ACK deadlock prevention

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Implements sync replication wait: primary blocks until at least one non-catching-up
standby ACKs the target LSN, or times out. Uses pthread_cond_timedwait with
CLOCK_REALTIME deadline. Inner loop rechecks all standbys after each wakeup to
guard against spurious wakeups.

ACK deadlock prevention: repl_on_ack() is called exclusively from the io_worker
read callback (not vtaskmgr), so it only does atomic_store + pthread_cond_signal —
safe to call while vcpu threads block in repl_wait_ack().

4 new TDD tests (all green, 9 total in test_repl_unit):
- test_wait_ack_no_standbys_returns_enodev
- test_wait_ack_already_acked
- test_wait_ack_timeout (verifies >=80ms elapsed)
- test_wait_ack_woken_by_background_ack (pthread thread signals after 30ms)
This commit is contained in:
Rongsong Shen 2026-05-07 17:23:50 +00:00
parent abefc8a128
commit d326ee1b2e
2 changed files with 144 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

59
src/controller/repl.c
View file

@ -201,12 +201,61 @@ int repl_broadcast(replicator_t *r, const wal_entry_hdr_t *hdr,
int repl_wait_ack(replicator_t *r, uint64_t target_lsn, uint32_t timeout_ms)
{
(void)r;
(void)target_lsn;
(void)timeout_ms;
if (!r) return -EINVAL;
/* Full implementation in P2-3 */
return -ENODEV;
/* Check whether any non-catching-up standby exists */
mylock_lock(&r->lock);
int has_standby = 0;
for (int i = 0; i < MAX_STANDBYS; i++) {
if (r->standbys[i].ep != NULL &&
!atomic_load_explicit(&r->standbys[i].in_catch_up,
memory_order_acquire)) {
has_standby = 1;
break;
}
}
mylock_unlock(&r->lock);
if (!has_standby) return -ENODEV;
/* Compute absolute deadline for pthread_cond_timedwait (CLOCK_REALTIME) */
struct timespec deadline;
clock_gettime(CLOCK_REALTIME, &deadline);
deadline.tv_sec += (long)(timeout_ms / 1000);
deadline.tv_nsec += (long)(timeout_ms % 1000) * 1000000L;
if (deadline.tv_nsec >= 1000000000L) {
deadline.tv_sec++;
deadline.tv_nsec -= 1000000000L;
}
pthread_mutex_lock(&r->ack_lock);
int rc = -ETIMEDOUT;
while (1) {
/* Recheck every standby after each wakeup (spurious-wakeup guard) */
mylock_lock(&r->lock);
for (int i = 0; i < MAX_STANDBYS; i++) {
standby_conn_t *s = &r->standbys[i];
if (s->ep == NULL) continue;
if (atomic_load_explicit(&s->in_catch_up, memory_order_acquire))
continue;
if (atomic_load_explicit(&s->acked_lsn, memory_order_acquire)
>= target_lsn) {
rc = 0;
break;
}
}
mylock_unlock(&r->lock);
if (rc == 0) break;
int wait_rc = pthread_cond_timedwait(&r->ack_cond, &r->ack_lock,
&deadline);
if (wait_rc == ETIMEDOUT) {
rc = -ETIMEDOUT;
break;
}
}
pthread_mutex_unlock(&r->ack_lock);
return rc;
}
/* ============================================================