1 files changed, 134 insertions, 0 deletions
diff --git a/libpthread/nptl/DESIGN-condvar.txt b/libpthread/nptl/DESIGN-condvar.txt
new file mode 100644
index 000000000..4845251c7
--- /dev/null
+++ b/libpthread/nptl/DESIGN-condvar.txt
@@ -0,0 +1,134 @@
+Conditional Variable pseudocode.
+================================
+
+       int pthread_cond_timedwait (pthread_cond_t *cv, pthread_mutex_t *mutex);
+       int pthread_cond_signal    (pthread_cond_t *cv);
+       int pthread_cond_broadcast (pthread_cond_t *cv);
+
+struct pthread_cond_t {
+
+   unsigned int cond_lock;
+
+         internal mutex
+
+   uint64_t total_seq;
+
+     Total number of threads using the conditional variable.
+
+   uint64_t wakeup_seq;
+
+     sequence number for next wakeup.
+
+   uint64_t woken_seq;
+
+     sequence number of last woken thread.
+
+   uint32_t broadcast_seq;
+
+}
+
+
+struct cv_data {
+
+   pthread_cond_t *cv;
+
+   uint32_t bc_seq
+
+}
+
+
+
+cleanup_handler(cv_data)
+{
+  cv = cv_data->cv;
+  lll_lock(cv->lock);
+
+  if (cv_data->bc_seq == cv->broadcast_seq) {
+    ++cv->wakeup_seq;
+    ++cv->woken_seq;
+  }
+
+  /* make sure no signal gets lost.  */
+  FUTEX_WAKE(cv->wakeup_seq, ALL);
+
+  lll_unlock(cv->lock);
+}
+
+
+cond_timedwait(cv, mutex, timeout):
+{
+   lll_lock(cv->lock);
+   mutex_unlock(mutex);
+
+   cleanup_push
+
+   ++cv->total_seq;
+   val = seq =  cv->wakeup_seq;
+   cv_data.bc = cv->broadcast_seq;
+   cv_data.cv = cv;
+
+   while (1) {
+
+     lll_unlock(cv->lock);
+
+     enable_async(&cv_data);
+
+     ret = FUTEX_WAIT(cv->wakeup_seq, val, timeout);
+
+     restore_async
+
+     lll_lock(cv->lock);
+
+     if (bc != cv->broadcast_seq)
+       goto bc_out;
+
+     val = cv->wakeup_seq;
+
+     if (val != seq && cv->woken_seq != val) {
+       ret = 0;
+       break;
+     }
+
+     if (ret == TIMEDOUT) {
+       ++cv->wakeup_seq;
+       break;
+     }
+   }
+
+   ++cv->woken_seq;
+
+ bc_out:
+   lll_unlock(cv->lock);
+
+   cleanup_pop
+
+   mutex_lock(mutex);
+
+   return ret;
+}
+
+cond_signal(cv)
+{
+   lll_lock(cv->lock);
+
+   if (cv->total_seq > cv->wakeup_seq) {
+     ++cv->wakeup_seq;
+     FUTEX_WAKE(cv->wakeup_seq, 1);
+   }
+
+   lll_unlock(cv->lock);
+}
+
+cond_broadcast(cv)
+{
+   lll_lock(cv->lock);
+
+   if (cv->total_seq > cv->wakeup_seq) {
+     cv->wakeup_seq = cv->total_seq;
+     cv->woken_seq = cv->total_seq;
+     ++cv->broadcast_seq;
+     FUTEX_WAKE(cv->wakeup_seq, ALL);
+   }
+
+   lll_unlock(cv->lock);
+}