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#include "pthread_impl.h"
static int vmlock[2];
void __vm_lock(int inc)
{
for (;;) {
int v = vmlock[0];
if (inc*v < 0) __wait(vmlock, vmlock+1, v, 1);
else if (a_cas(vmlock, v, v+inc)==v) break;
}
}
void __vm_unlock(void)
{
if (vmlock[0]>0) a_dec(vmlock);
else a_inc(vmlock);
if (vmlock[1]) __wake(vmlock, 1, 1);
}
static int pshared_barrier_wait(pthread_barrier_t *b)
{
int limit = (b->_b_limit & INT_MAX) + 1;
int seq;
int ret = 0;
if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
while (a_swap(&b->_b_lock, 1))
__wait(&b->_b_lock, &b->_b_waiters, 1, 0);
seq = b->_b_seq;
if (++b->_b_count == limit) {
ret = PTHREAD_BARRIER_SERIAL_THREAD;
b->_b_seq++;
__wake(&b->_b_seq, -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);
}
__vm_lock(+1);
if (a_fetch_add(&b->_b_count, -1)==1) {
b->_b_seq++;
__wake(&b->_b_seq, -1, 0);
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
} else {
__wait(&b->_b_seq, 0, seq+1, 0);
}
__vm_unlock();
return 0;
}
struct instance
{
int count;
int last;
int waiters;
int finished;
};
int pthread_barrier_wait(pthread_barrier_t *b)
{
int limit = b->_b_limit;
struct instance *inst;
/* Trivial case: count was set at 1 */
if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
/* Process-shared barriers require a separate, inefficient wait */
if (limit < 0) return pshared_barrier_wait(b);
/* Otherwise we need a lock on the barrier object */
while (a_swap(&b->_b_lock, 1))
__wait(&b->_b_lock, &b->_b_waiters, 1, 1);
inst = b->_b_inst;
/* First thread to enter the barrier becomes the "instance owner" */
if (!inst) {
struct instance new_inst = { 0 };
int spins = 10000;
b->_b_inst = inst = &new_inst;
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
while (spins-- && !inst->finished)
a_spin();
a_inc(&inst->finished);
while (inst->finished == 1)
__syscall(SYS_futex, &inst->finished, FUTEX_WAIT,1,0);
return PTHREAD_BARRIER_SERIAL_THREAD;
}
/* Last thread to enter the barrier wakes all non-instance-owners */
if (++inst->count == limit) {
b->_b_inst = 0;
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
a_store(&inst->last, 1);
if (inst->waiters)
__wake(&inst->last, -1, 1);
} else {
a_store(&b->_b_lock, 0);
if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
__wait(&inst->last, &inst->waiters, 0, 1);
}
/* Last thread to exit the barrier wakes the instance owner */
if (a_fetch_add(&inst->count,-1)==1 && a_fetch_add(&inst->finished,1))
__wake(&inst->finished, 1, 1);
return 0;
}
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