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-rw-r--r--src/thread/pthread_barrier_wait.c60
1 files changed, 44 insertions, 16 deletions
diff --git a/src/thread/pthread_barrier_wait.c b/src/thread/pthread_barrier_wait.c
index 7bfadb95..1e638d96 100644
--- a/src/thread/pthread_barrier_wait.c
+++ b/src/thread/pthread_barrier_wait.c
@@ -1,31 +1,59 @@
#include "pthread_impl.h"
+struct instance
+{
+ int count;
+ int last;
+ int waiters;
+ int finished;
+};
+
int pthread_barrier_wait(pthread_barrier_t *b)
{
- int cur;
+ int limit = b->_b_limit;
+ struct instance *inst;
/* Trivial case: count was set at 1 */
- if (!b->_b_limit) return PTHREAD_BARRIER_SERIAL_THREAD;
+ if (!limit) return PTHREAD_BARRIER_SERIAL_THREAD;
- /* Wait for anyone still suspended at previous use of barrier */
- while ((cur=b->_b_left))
- __wait(&b->_b_left, &b->_b_waiters, cur, 0);
+ /* Otherwise we need a lock on the barrier object */
+ while (a_swap(&b->_b_lock, 1))
+ __wait(&b->_b_lock, &b->_b_waiters, 1, 0);
+ inst = b->_b_inst;
- /* If we are the last to reach barrier, reset it and wake others */
- if (a_fetch_add(&b->_b_count, 1) == b->_b_limit) {
- b->_b_left = b->_b_limit;
- b->_b_count = 0;
- __wake(&b->_b_count, -1, 0);
+ /* 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, 0);
+ 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;
}
- /* Wait for our peers to reach the barrier */
- while ((cur=b->_b_count))
- __wait(&b->_b_count, 0, cur, 0);
+ /* Last thread to enter the barrier wakes all non-instance-owners */
+ if (++inst->count == limit) {
+a_spin(); a_spin();
+ b->_b_inst = 0;
+ a_store(&b->_b_lock, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+ a_store(&inst->last, 1);
+ if (inst->waiters)
+ __wake(&inst->last, -1, 0);
+ } else {
+ a_store(&b->_b_lock, 0);
+ if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+ __wait(&inst->last, &inst->waiters, 0, 0);
+ }
- /* If we're the last to wake up and barrier is awaiting reuse */
- if (a_fetch_add(&b->_b_left, -1) == 1 && b->_b_waiters)
- __wake(&b->_b_left, -1, 0);
+ /* 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, 0);
return 0;
}