Fix up checking for empty to account for stub messages.

src/mem/globalalloc.h

@@ -107,41 +107,43 @@ namespace snmalloc
 #endif
     }
 
-    void debug_check_empty()
+    /**
+      If you pass a pointer to a bool, then it returns whether all the allocators are empty.
+      If you don't pass a pointer to a bool, then will raise an error all the allocators are
+      not empty.
+     */
+    void debug_check_empty(bool* result = nullptr)
     {
 #ifndef USE_MALLOC
       // This is a debugging function. It checks that all memory from all
       // allocators has been freed.
-      size_t alloc_count = 0;
-
       auto* alloc = Parent::iterate();
 
-      // Count the linked allocators.
-      while (alloc != nullptr)
-      {
-        alloc = Parent::iterate(alloc);
-        alloc_count++;
-      }
-
       bool done = false;
 
+      size_t non_empty_count = 0;
       while (!done)
       {
         done = true;
         alloc = Parent::iterate();
+        non_empty_count = 0;
 
         while (alloc != nullptr)
         {
           // Destroy the message queue so that it has no stub message.
           Remote* p = alloc->message_queue().destroy();
 
-          while (p != nullptr)
+            while (p != nullptr)
           {
             Remote* next = p->non_atomic_next;
             alloc->handle_dealloc_remote(p);
             p = next;
           }
 
+          // Check that the allocator has freed all memory.
+          if (!alloc->stats().is_empty())
+            non_empty_count++;
+
           // Place the static stub message on the queue.
           alloc->init_message_queue();
 
@@ -158,20 +160,16 @@ namespace snmalloc
         }
       }
 
-      alloc = Parent::iterate();
-      size_t empty_count = 0;
-
-      while (alloc != nullptr)
+      if (result != nullptr)
       {
-        // Check that the allocator has freed all memory.
-        if (alloc->stats().is_empty())
-          empty_count++;
-
-        alloc = Parent::iterate(alloc);
+        *result = non_empty_count == 0;
+        return;
       }
 
-      if (alloc_count != empty_count)
-        error("Incorrect number of allocators");
+      if (non_empty_count != 0)
+      {
+        error("debug_check_empty: found non-empty allocators");
+      }
 #endif
     }
   };