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Use more specific memory ordering. 

- other threads need to see the correct value of p->files, so use
  'release' in the parent cleanup section
- recurse_into_parents needs to see the correct value of p->files, so
  use 'acquire' there
- also add comments explaining each branch in the parent cleanup section
This commit is contained in:
Érico Nogueira 2022-06-12 21:25:34 -03:00
parent 657fd48d42
commit 2fbe3a2789
1 changed files with 4 additions and 2 deletions
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6
remove.c
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@ -101,7 +101,7 @@ static inline void recurse_into_parents(struct task *t)
while ((recurse = recurse->parent)) {
free(free_list); free_list = NULL;
unsigned rc = atomic_fetch_add_explicit(&recurse->removed_count, 1, memory_order_acq_rel);
unsigned rc = atomic_fetch_add_explicit(&recurse->removed_count, 1, memory_order_acquire);
if (rc & ACQUIRED) break;
printf("parent: removed %04d total %04d '%s'\n", rc, recurse->files, recurse->path);
@ -193,15 +193,17 @@ fast_path_dir:
if (p) {
p->files = n-1; /* other thread will compare against removed_count-1 */
unsigned rc = atomic_fetch_and_explicit(&p->removed_count, ~ACQUIRED, memory_order_acq_rel);
unsigned rc = atomic_fetch_and_explicit(&p->removed_count, ~ACQUIRED, memory_order_release);
if (rc == (n|ACQUIRED)) {
free(p);
/* this branch is taken when other threads have already removed all of p's children */
if (rmdir(t.path)) {
fprintf(stderr, "atomic rmdir failed '%s': %m\n", t.path);
} else {
printf("atomic rmdir succeeded '%s'\n", t.path);
}
} else {
/* we can't recurse into p's parent if p still has children that need to be removed */
continue;
}
} else {