[352] | 1 | #include "pthread_impl.h"
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| 2 |
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| 3 | static int pshared_barrier_wait(pthread_barrier_t *b)
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| 4 | {
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| 5 | int limit = (b->_b_limit & INT_MAX) + 1;
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| 6 | int ret = 0;
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| 7 | int v, w;
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| 8 |
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| 9 | if (limit==1) return PTHREAD_BARRIER_SERIAL_THREAD;
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| 10 |
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| 11 | while ((v=a_cas(&b->_b_lock, 0, limit)))
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| 12 | __wait(&b->_b_lock, &b->_b_waiters, v, 0);
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| 13 |
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| 14 | /* Wait for <limit> threads to get to the barrier */
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| 15 | if (++b->_b_count == limit) {
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| 16 | a_store(&b->_b_count, 0);
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| 17 | ret = PTHREAD_BARRIER_SERIAL_THREAD;
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| 18 | if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
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| 19 | } else {
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| 20 | a_store(&b->_b_lock, 0);
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| 21 | if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
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| 22 | while ((v=b->_b_count)>0)
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| 23 | __wait(&b->_b_count, &b->_b_waiters2, v, 0);
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| 24 | }
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| 25 |
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| 26 | __vm_lock();
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| 27 |
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| 28 | /* Ensure all threads have a vm lock before proceeding */
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| 29 | if (a_fetch_add(&b->_b_count, -1)==1-limit) {
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| 30 | a_store(&b->_b_count, 0);
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| 31 | if (b->_b_waiters2) __wake(&b->_b_count, -1, 0);
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| 32 | } else {
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| 33 | while ((v=b->_b_count))
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| 34 | __wait(&b->_b_count, &b->_b_waiters2, v, 0);
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| 35 | }
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| 36 |
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| 37 | /* Perform a recursive unlock suitable for self-sync'd destruction */
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| 38 | do {
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| 39 | v = b->_b_lock;
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| 40 | w = b->_b_waiters;
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| 41 | } while (a_cas(&b->_b_lock, v, v==INT_MIN+1 ? 0 : v-1) != v);
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| 42 |
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| 43 | /* Wake a thread waiting to reuse or destroy the barrier */
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| 44 | if (v==INT_MIN+1 || (v==1 && w))
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| 45 | __wake(&b->_b_lock, 1, 0);
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| 46 |
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| 47 | __vm_unlock();
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| 48 |
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| 49 | return ret;
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| 50 | }
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| 51 |
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| 52 | struct instance
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| 53 | {
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| 54 | volatile int count;
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| 55 | volatile int last;
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| 56 | volatile int waiters;
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| 57 | volatile int finished;
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| 58 | };
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| 59 |
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| 60 | int pthread_barrier_wait(pthread_barrier_t *b)
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| 61 | {
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| 62 | int limit = b->_b_limit;
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| 63 | struct instance *inst;
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| 64 |
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| 65 | /* Trivial case: count was set at 1 */
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| 66 | if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
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| 67 |
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| 68 | /* Process-shared barriers require a separate, inefficient wait */
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| 69 | if (limit < 0) return pshared_barrier_wait(b);
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| 70 |
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| 71 | /* Otherwise we need a lock on the barrier object */
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| 72 | while (a_swap(&b->_b_lock, 1))
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| 73 | __wait(&b->_b_lock, &b->_b_waiters, 1, 1);
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| 74 | inst = b->_b_inst;
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| 75 |
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| 76 | /* First thread to enter the barrier becomes the "instance owner" */
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| 77 | if (!inst) {
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| 78 | struct instance new_inst = { 0 };
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| 79 | int spins = 200;
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| 80 | b->_b_inst = inst = &new_inst;
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| 81 | a_store(&b->_b_lock, 0);
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| 82 | if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
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| 83 | while (spins-- && !inst->finished)
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| 84 | a_spin();
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| 85 | a_inc(&inst->finished);
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| 86 | while (inst->finished == 1)
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| 87 | __syscall(SYS_futex,&inst->finished,FUTEX_WAIT|FUTEX_PRIVATE,1,0) != -ENOSYS
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| 88 | || __syscall(SYS_futex,&inst->finished,FUTEX_WAIT,1,0);
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| 89 | return PTHREAD_BARRIER_SERIAL_THREAD;
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| 90 | }
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| 91 |
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| 92 | /* Last thread to enter the barrier wakes all non-instance-owners */
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| 93 | if (++inst->count == limit) {
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| 94 | b->_b_inst = 0;
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| 95 | a_store(&b->_b_lock, 0);
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| 96 | if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
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| 97 | a_store(&inst->last, 1);
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| 98 | if (inst->waiters)
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| 99 | __wake(&inst->last, -1, 1);
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| 100 | } else {
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| 101 | a_store(&b->_b_lock, 0);
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| 102 | if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
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| 103 | __wait(&inst->last, &inst->waiters, 0, 1);
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| 104 | }
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| 105 |
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| 106 | /* Last thread to exit the barrier wakes the instance owner */
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| 107 | if (a_fetch_add(&inst->count,-1)==1 && a_fetch_add(&inst->finished,1))
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| 108 | __wake(&inst->finished, 1, 1);
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| 109 |
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| 110 | return 0;
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| 111 | }
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