---

yaml
---
r: 31659
b: refs/heads/dist-snap
c: 86947e4
h: refs/heads/master
i:
  31657: c531fce
  31655: fa53e97
v: v3

Author: eholk

[refs]

@@ -7,6 +7,6 @@ refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: d0c6ce338884ee21843f4b40bf6bf18d222ce5df
 refs/heads/incoming: d9317a174e434d4c99fc1a37fd7dc0d2f5328d37
-refs/heads/dist-snap: d8e9724fb1b14a415d922431a5bc74f937c9ff38
+refs/heads/dist-snap: 86947e47ad057d50209cf8a022f088c22089433f
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503

branches/dist-snap/src/libcore/pipes.rs

@@ -41,6 +41,21 @@ buffer that is carried along in the endpoint data structures.
 
 FIXME (#3072) - This is still incomplete
 
+
+
+## Invariants
+
+This section attempts to document the invariants that must hold to
+avoid races. These primarily deal with the state and blocked_task
+fields on packet_headers.
+
+1. If the sender reads a some(task) out of blocked_task, then the task
+that is pointed there will remain live for any events that the sender
+might signal.
+
+2. The sender may only read the blocked_task field if it first ensures
+that the packet's state field is blocked.
+
 */
 
 import unsafe::{forget, reinterpret_cast, transmute};

branches/dist-snap/src/rt/rust_task.cpp

@@ -678,11 +678,11 @@ MUST_CHECK bool rust_task::wait_event(void **result) {
 
 void
 rust_task::signal_event(void *event) {
-    scoped_lock with(lifecycle_lock);
-
     assert(task_state_blocked == state ||
            task_state_running == state);
 
+    scoped_lock with(lifecycle_lock);
+
     this->event = event;
     event_reject = true;
     if(task_state_blocked == state) {