std::rt: Add JoinLatch

This is supposed to be an efficient way to link the lifetimes
of tasks into a tree. JoinLatches form a tree and when `release`
is called they wait on children then signal the parent.

This structure creates zombie tasks which currently keep the entire
task allocated. Zombie tasks are supposed to be tombstoned but that
code does not work correctly.

1 files changed, 4 insertions, 1 deletions

diff --git a/src/libstd/rt/sched.rs b/src/libstd/rt/sched.rs
index 97a1c26ed4d..104eb4b8bae 100644
--- a/src/libstd/rt/sched.rs
+++ b/src/libstd/rt/sched.rs
@@ -151,7 +151,10 @@ pub impl Scheduler {
         // XXX: Reenable this once we're using a per-task queue. With a shared
         // queue this is not true
         //assert!(sched.work_queue.is_empty());
-        rtdebug!("scheduler metrics: %s\n", sched.metrics.to_str());
+        rtdebug!("scheduler metrics: %s\n", {
+            use to_str::ToStr;
+            sched.metrics.to_str()
+        });
         return sched;
     }