Fix race condition in Redirection global list using CAS.

runtime/vm/simulator_arm.cc

Index: runtime/vm/simulator_arm.cc
===================================================================
--- runtime/vm/simulator_arm.cc	(revision 43532)
+++ runtime/vm/simulator_arm.cc	(working copy)
@@ -811,9 +811,18 @@
       : external_function_(external_function),
         call_kind_(call_kind),
         argument_count_(argument_count),
-        svc_instruction_(Instr::kSimulatorRedirectInstruction),
-        next_(list_) {
-    list_ = this;
+        svc_instruction_(Instr::kSimulatorRedirectInstruction) {
+    // Atomically prepend this element to the front of the global list.
+    // Note: Since elements are never removed, there is no ABA issue.
+    Redirection* old_list = list_;
+    do {
+      next_ = old_list;

[Cutch, 2015/02/06 00:47:10]

consider renaming "old_list" to "list_head".

[koda, 2015/02/06 15:50:22]

Done.

+      old_list = reinterpret_cast<Redirection*>(
+          AtomicOperations::CompareAndSwapWord(
+              reinterpret_cast<uword*>(&list_),
+              reinterpret_cast<uword>(next_),
+              reinterpret_cast<uword>(this)));
+    } while (old_list != next_);
   }
 
   uword external_function_;