eliminate the sequence number field and instead use the counter as the
futex because of the way the lock is held, sequence numbers are
completely useless, and this frees up a field in the barrier structure
to be used as a waiter count for the count futex, which lets us avoid
some syscalls in the best case.
as of now, self-synchronized destruction and unmapping should be fully
safe. before any thread can return from the barrier, all threads in
the barrier have obtained the vm lock, and each holds a shared lock on
the barrier. the barrier memory is not inspected after the shared lock
count reaches 0, nor after the vm lock is released.
#define _b_waiters __u.__i[1]
#define _b_limit __u.__i[2]
#define _b_count __u.__i[3]
#define _b_waiters __u.__i[1]
#define _b_limit __u.__i[2]
#define _b_count __u.__i[3]
-#define _b_seq __u.__i[4]
+#define _b_waiters2 __u.__i[4]
#define _b_inst __u.__p[4]
#include "pthread_arch.h"
#define _b_inst __u.__p[4]
#include "pthread_arch.h"
static int pshared_barrier_wait(pthread_barrier_t *b)
{
int limit = (b->_b_limit & INT_MAX) + 1;
static int pshared_barrier_wait(pthread_barrier_t *b)
{
int limit = (b->_b_limit & INT_MAX) + 1;
while ((v=a_cas(&b->_b_lock, 0, limit)))
__wait(&b->_b_lock, &b->_b_waiters, v, 0);
while ((v=a_cas(&b->_b_lock, 0, limit)))
__wait(&b->_b_lock, &b->_b_waiters, v, 0);
+ /* Wait for <limit> threads to get to the barrier */
if (++b->_b_count == limit) {
if (++b->_b_count == limit) {
+ a_store(&b->_b_count, 0);
ret = PTHREAD_BARRIER_SERIAL_THREAD;
ret = PTHREAD_BARRIER_SERIAL_THREAD;
- b->_b_seq++;
- __wake(&b->_b_seq, -1, 0);
+ if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
} else {
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
} else {
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
- __wait(&b->_b_seq, 0, seq, 0);
+ while ((v=b->_b_count)>0)
+ __wait(&b->_b_count, &b->_b_waiters2, v, 0);
- if (a_fetch_add(&b->_b_count, -1)==1) {
- b->_b_seq++;
- __wake(&b->_b_seq, -1, 0);
+ /* Ensure all threads have a vm lock before proceeding */
+ if (a_fetch_add(&b->_b_count, -1)==1-limit) {
+ a_store(&b->_b_count, 0);
+ if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
- __wait(&b->_b_seq, 0, seq+1, 0);
+ while ((v=b->_b_count))
+ __wait(&b->_b_count, &b->_b_waiters2, v, 0);
}
/* Perform a recursive unlock suitable for self-sync'd destruction */
do {
v = b->_b_lock;
w = b->_b_waiters;
}
/* Perform a recursive unlock suitable for self-sync'd destruction */
do {
v = b->_b_lock;
w = b->_b_waiters;
- } while (a_cas(&b->_b_lock, v, v-1 & INT_MAX) != v);
+ } while (a_cas(&b->_b_lock, v, v==INT_MIN+1 ? 0 : v-1) != v);
+ /* Wake a thread waiting to reuse or destroy the barrier */
if (v==INT_MIN+1 || (v==1 && w))
__wake(&b->_b_lock, 1, 0);
if (v==INT_MIN+1 || (v==1 && w))
__wake(&b->_b_lock, 1, 0);