fix excessive/insufficient wakes in __vm_unlock

[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..6052925 100644 (file)
--- a/src/thread/pthread_barrier_wait.c
+++ b/src/thread/pthread_barrier_wait.c
@@ -1,5 +1,72 @@
 #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)
+{
+       int inc = vmlock[0]>0 ? -1 : 1;
+       if (a_fetch_add(vmlock, inc)==-inc && vmlock[1])
+               __wake(vmlock, -1, 1);
+}
+
+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(+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();
+
+       return ret;
+}
+
 struct instance
 {
        int count;
@@ -16,9 +83,12 @@ 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 +97,7 @@ 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 +110,19 @@ 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;
 }