native: Don't deadlock the runtime on spawn failure

Previously, the call to bookkeeping::increment() was never paired with a
decrement when the spawn failed (due to unwinding). This fixes the problem by
returning a "bomb" from increment() which will decrement on drop, and then
moving the bomb into the child task's procedure which will be dropped naturally.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libnative/task.rs b/src/libnative/task.rs
index 35367ff2efa..c72d6c24a7c 100644
--- a/src/libnative/task.rs
+++ b/src/libnative/task.rs
@@ -71,7 +71,7 @@ pub fn spawn_opts(opts: TaskOpts, f: proc():Send) {
     // Note that this increment must happen *before* the spawn in order to
     // guarantee that if this task exits it will always end up waiting for the
     // spawned task to exit.
-    bookkeeping::increment();
+    let token = bookkeeping::increment();
 
     // Spawning a new OS thread guarantees that __morestack will never get
     // triggered, but we must manually set up the actual stack bounds once this
@@ -93,7 +93,7 @@ pub fn spawn_opts(opts: TaskOpts, f: proc():Send) {
         let mut task = task;
         task.put_runtime(ops);
         drop(task.run(|| { f.take_unwrap()() }).destroy());
-        bookkeeping::decrement();
+        drop(token);
     })
 }