1#include "pthread_impl.h" 2 3static int pshared_barrier_wait(pthread_barrier_t *b) 4{ 5 int limit = (b->_b_limit & INT_MAX) + 1; 6 int ret = 0; 7 int v, w; 8 9 if (limit==1) return PTHREAD_BARRIER_SERIAL_THREAD; 10 11 while ((v=a_cas(&b->_b_lock, 0, limit))) 12 __wait(&b->_b_lock, &b->_b_waiters, v, 0); 13 14 /* Wait for <limit> threads to get to the barrier */ 15 if (++b->_b_count == limit) { 16 a_store(&b->_b_count, 0); 17 ret = PTHREAD_BARRIER_SERIAL_THREAD; 18 if (b->_b_waiters2) __wake(&b->_b_count, -1, 0); 19 } else { 20 a_store(&b->_b_lock, 0); 21 if (b->_b_waiters) __wake(&b->_b_lock, 1, 0); 22 while ((v=b->_b_count)>0) 23 __wait(&b->_b_count, &b->_b_waiters2, v, 0); 24 } 25 26 __vm_lock(); 27 28 /* Ensure all threads have a vm lock before proceeding */ 29 if (a_fetch_add(&b->_b_count, -1)==1-limit) { 30 a_store(&b->_b_count, 0); 31 if (b->_b_waiters2) __wake(&b->_b_count, -1, 0); 32 } else { 33 while ((v=b->_b_count)) 34 __wait(&b->_b_count, &b->_b_waiters2, v, 0); 35 } 36 37 /* Perform a recursive unlock suitable for self-sync'd destruction */ 38 do { 39 v = b->_b_lock; 40 w = b->_b_waiters; 41 } while (a_cas(&b->_b_lock, v, v==INT_MIN+1 ? 0 : v-1) != v); 42 43 /* Wake a thread waiting to reuse or destroy the barrier */ 44 if (v==INT_MIN+1 || (v==1 && w)) 45 __wake(&b->_b_lock, 1, 0); 46 47 __vm_unlock(); 48 49 return ret; 50} 51 52struct instance 53{ 54 volatile int count; 55 volatile int last; 56 volatile int waiters; 57 volatile int finished; 58}; 59 60int pthread_barrier_wait(pthread_barrier_t *b) 61{ 62 int limit = b->_b_limit; 63 struct instance *inst; 64 65 /* Trivial case: count was set at 1 */ 66 if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD; 67 68 /* Process-shared barriers require a separate, inefficient wait */ 69 if (limit < 0) return pshared_barrier_wait(b); 70 71 /* Otherwise we need a lock on the barrier object */ 72 while (a_swap(&b->_b_lock, 1)) 73 __wait(&b->_b_lock, &b->_b_waiters, 1, 1); 74 inst = b->_b_inst; 75 76 /* First thread to enter the barrier becomes the "instance owner" */ 77 if (!inst) { 78 struct instance new_inst = { 0 }; 79 int spins = 200; 80 b->_b_inst = inst = &new_inst; 81 a_store(&b->_b_lock, 0); 82 if (b->_b_waiters) __wake(&b->_b_lock, 1, 1); 83 while (spins-- && !inst->finished) 84 a_spin(); 85 a_inc(&inst->finished); 86 while (inst->finished == 1) 87 __syscall(SYS_futex,&inst->finished,FUTEX_WAIT|128,1,0) != -ENOSYS 88 || __syscall(SYS_futex,&inst->finished,FUTEX_WAIT,1,0); 89 return PTHREAD_BARRIER_SERIAL_THREAD; 90 } 91 92 /* Last thread to enter the barrier wakes all non-instance-owners */ 93 if (++inst->count == limit) { 94 b->_b_inst = 0; 95 a_store(&b->_b_lock, 0); 96 if (b->_b_waiters) __wake(&b->_b_lock, 1, 1); 97 a_store(&inst->last, 1); 98 if (inst->waiters) 99 __wake(&inst->last, -1, 1); 100 } else { 101 a_store(&b->_b_lock, 0); 102 if (b->_b_waiters) __wake(&b->_b_lock, 1, 1); 103 __wait(&inst->last, &inst->waiters, 0, 1); 104 } 105 106 /* Last thread to exit the barrier wakes the instance owner */ 107 if (a_fetch_add(&inst->count,-1)==1 && a_fetch_add(&inst->finished,1)) 108 __wake(&inst->finished, 1, 1); 109 110 return 0; 111} 112