| #include "pthread_impl.h" |
| |
| void __vm_lock_impl(int); |
| void __vm_unlock_impl(void); |
| |
| static int pshared_barrier_wait(pthread_barrier_t *b) |
| { |
| int limit = (b->_b_limit & INT_MAX) + 1; |
| int ret = 0; |
| int v, w; |
| |
| if (limit==1) return PTHREAD_BARRIER_SERIAL_THREAD; |
| |
| 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) { |
| a_store(&b->_b_count, 0); |
| ret = PTHREAD_BARRIER_SERIAL_THREAD; |
| 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); |
| while ((v=b->_b_count)>0) |
| __wait(&b->_b_count, &b->_b_waiters2, v, 0); |
| } |
| |
| __vm_lock_impl(+1); |
| |
| /* 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); |
| } else { |
| 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; |
| } 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); |
| |
| __vm_unlock_impl(); |
| |
| return ret; |
| } |
| |
| 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; |
| } |