Tweak ordering for releasing ThreadNexus lock.

machine/thread_nexus.cpp

@@ -205,21 +205,21 @@ namespace rubinius {
       id = 0;
     }
 
-    /* Lock and hold the waiting_mutex to prevent any other thread from
-     * holding it across a fork() call.
-     */
+    // Checkpoint all the other threads.
     ns = 0;
 
-    while(!waiting_mutex_.try_lock()) {
+    while(!try_checkpoint(vm)) {
       ns += delay();
 
       detect_deadlock(ns, lock_limit);
     }
 
-    // Checkpoint all the other threads.
+    /* Lock and hold the waiting_mutex to prevent any other thread from
+     * holding it across a fork() call.
+     */
     ns = 0;
 
-    while(!try_checkpoint(vm)) {
+    while(!waiting_mutex_.try_lock()) {
       ns += delay();
 
       detect_deadlock(ns, lock_limit);

machine/thread_nexus.hpp

@@ -157,8 +157,8 @@ namespace rubinius {
 
     void unlock() {
       std::lock_guard<std::mutex> guard(waiting_mutex_);
-      phase_flag_ = 0;
       waiting_condition_.notify_all();
+      phase_flag_ = 0;
     }
 
     bool try_checkpoint(VM* vm);