process-shared barrier support, based on discussion with bdonlan

[musl] / src / thread / pthread_barrier_wait.c

diff --git a/src/thread/pthread_barrier_wait.c b/src/thread/pthread_barrier_wait.c
index aed1adc..db432ba 100644 (file)
--- a/src/thread/pthread_barrier_wait.c
+++ b/src/thread/pthread_barrier_wait.c
@@ -1,5 +1,62 @@
 #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;
@@ -16,9 +73,12 @@ int pthread_barrier_wait(pthread_barrier_t *b)
        /* 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, 0);
+               __wait(&b->_b_lock, &b->_b_waiters, 1, 1);
        inst = b->_b_inst;
 
        /* First thread to enter the barrier becomes the "instance owner" */
@@ -27,7 +87,7 @@ int pthread_barrier_wait(pthread_barrier_t *b)
                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);
+               if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
                while (spins-- && !inst->finished)
                        a_spin();
                a_inc(&inst->finished);
@@ -40,19 +100,19 @@ int pthread_barrier_wait(pthread_barrier_t *b)
        if (++inst->count == limit) {
                b->_b_inst = 0;
                a_store(&b->_b_lock, 0);
-               if (b->_b_waiters) __wake(&b->_b_lock, 1, 0);
+               if (b->_b_waiters) __wake(&b->_b_lock, 1, 1);
                a_store(&inst->last, 1);
                if (inst->waiters)
-                       __wake(&inst->last, -1, 0);
+                       __wake(&inst->last, -1, 1);
        } 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 (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, 0);
+               __wake(&inst->finished, 1, 1);
 
        return 0;
 }