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fixed race condition

This commit is contained in:
aiden 2023-03-01 11:07:07 +00:00
parent 117cf4e63e
commit 3a28635648
Signed by: aiden
GPG Key ID: EFA9C74AEBF806E0
1 changed files with 17 additions and 7 deletions
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24
ifc.h
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@ -32,8 +32,11 @@ struct ifc_head {
const unsigned short int padding_sz;
};
struct ifc_tid {
// occupied is conceptually a mutex (for the area itself)
size_t occupied;
// tid depends on tid_valid
pthread_t tid;
bool tid_valid;
};
#define _ifc_iter(ifc, area) *area = NULL; (area = ifc_reap(ifc, area)) != NULL;)
@ -115,6 +118,7 @@ static struct ifc *ifc_alloc(unsigned int n, unsigned short int sz) {
struct ifc_tid *tid = IFC_TID(ifc);
for (unsigned int idx = 0; idx < n; ++idx) {
tid[idx].occupied = 0;
tid[idx].tid_valid = false;
}
// IFC_AREAS are purposefully uninitialised
return (struct ifc *)ifc;
@ -130,10 +134,16 @@ static void *ifc_area(struct ifc *ifc) {
struct ifc_tid *tid = IFC_TID(ifc);
for (unsigned int idx = 0; idx < n; ++idx) {
size_t *occupied = &(tid[idx].occupied);
if (!__atomic_load_n(occupied, __ATOMIC_RELAXED)) {
if (!__atomic_load_n(occupied, __ATOMIC_ACQUIRE)) {
likely_unoccupied = idx;
continue;
}
// acquire to ensure that `tid` is
// not loaded before `tid_valid`
if (!__atomic_load_n(&(tid[idx].tid_valid), __ATOMIC_ACQUIRE)) {
continue;
}
if (pthread_equal(tid[idx].tid, self)) {
__atomic_add_fetch(occupied, 1, __ATOMIC_RELAXED);
return IFC_AREA(ifc, idx);
@ -144,6 +154,7 @@ static void *ifc_area(struct ifc *ifc) {
size_t zero = 0;
if (__atomic_compare_exchange_n(&(tid[idx].occupied), &(zero), 1, false, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
tid[idx].tid = self;
__atomic_store_n(&(tid[idx].tid_valid), true, __ATOMIC_RELEASE);
return IFC_AREA(ifc, idx);
}
}
@ -151,13 +162,13 @@ static void *ifc_area(struct ifc *ifc) {
size_t zero = 0;
if (__atomic_compare_exchange_n(&(tid[idx].occupied), &(zero), 1, false, __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
tid[idx].tid = self;
__atomic_store_n(&(tid[idx].tid_valid), true, __ATOMIC_RELEASE);
return IFC_AREA(ifc, idx);
}
}
return NULL;
}
static void ifc_release_clean(struct ifc *ifc, void *area, ifc_clean clean, void *clean_arg) {
struct ifc_head *head = IFC_HEAD(ifc);
struct ifc_tid *tid = IFC_TID(ifc);
@ -165,17 +176,16 @@ static void ifc_release_clean(struct ifc *ifc, void *area, ifc_clean clean, void
assert(pthread_equal(tid[idx].tid, pthread_self()));
size_t *occupied = &(tid[idx].occupied);
size_t capture = __atomic_load_n(occupied, __ATOMIC_RELAXED);
int memorder;
if (capture == 1) {
if (clean != NULL) {
clean(area, clean_arg);
}
memorder = __ATOMIC_RELEASE;
__atomic_store_n(&(tid[idx].tid_valid), false, __ATOMIC_RELEASE);
__atomic_store_n(occupied, 0, __ATOMIC_RELEASE);
} else {
assert(capture != 0);
memorder = __ATOMIC_RELAXED;
__atomic_sub_fetch(occupied, 1, __ATOMIC_RELAXED);
}
__atomic_sub_fetch(occupied, 1, memorder);
return;
}
#define ifc_release(ifc, area) ifc_release_clean(ifc, area, NULL, NULL)
@ -195,4 +205,4 @@ static inline void *ifc_reap(struct ifc *ifc, void *area) {
return area;
}
#endif
#endif