From: Martin Quinson <martin.quinson@loria.fr>
Date: Wed, 26 Apr 2017 14:50:57 +0000 (+0200)
Subject: Strengthen the memory ordering order on that refcounting to work around a bug
X-Git-Tag: v3.16~308
X-Git-Url: http://info.iut-bm.univ-fcomte.fr/pub/gitweb/simgrid.git/commitdiff_plain/fa61108e3d288e7e5559992a1feb7c86e255b3e3?ds=inline

Strengthen the memory ordering order on that refcounting to work around a bug
---

diff --git a/src/simix/ActorImpl.hpp b/src/simix/ActorImpl.hpp
index 3e0f707c0a..e1ffbdac9f 100644
--- a/src/simix/ActorImpl.hpp
+++ b/src/simix/ActorImpl.hpp
@@ -73,13 +73,17 @@ private:
 public:
   friend void intrusive_ptr_add_ref(ActorImpl* process)
   {
-    process->refcount_.fetch_add(1, std::memory_order_relaxed);
+    // std::memory_order_relaxed ought to be enough here instead of std::memory_order_seq_cst
+    // But then, we have a threading issue when an actor commits a suicide:
+    //  it seems that in this case, the worker thread kills the last occurrence of the actor
+    //  while usually, the maestro does so. FIXME: we should change how actors suicide
+    process->refcount_.fetch_add(1, std::memory_order_seq_cst);
   }
   friend void intrusive_ptr_release(ActorImpl* process)
   {
     // inspired from http://www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html
     if (process->refcount_.fetch_sub(1, std::memory_order_release) == 1) {
-      // Make sure that any changes done on other threads before their acquire are commited before our delete
+      // Make sure that any changes done on other threads before their acquire are committed before our delete
       // http://stackoverflow.com/questions/27751025/why-is-an-acquire-barrier-needed-before-deleting-the-data-in-an-atomically-refer
       std::atomic_thread_fence(std::memory_order_acquire);
       delete process;