1 files changed, 18 insertions, 3 deletions
diff --git a/include/mbgl/actor/mailbox.hpp b/include/mbgl/actor/mailbox.hpp
index 8ecf91701a..23c579917a 100644
--- a/include/mbgl/actor/mailbox.hpp
+++ b/include/mbgl/actor/mailbox.hpp
@@ -1,5 +1,7 @@
 #pragma once
 
+#include <mbgl/util/optional.hpp>
+
 #include <memory>
 #include <mutex>
 #include <queue>
@@ -11,17 +13,30 @@ class Message;
 
 class Mailbox : public std::enable_shared_from_this<Mailbox> {
 public:
+   
+    // Create a "holding" mailbox, messages to which will remain queued,
+    // unconsumed, until the mailbox is associated with a Scheduler using
+    // start(). This allows a Mailbox object to be created on one thread and
+    // later transferred to a different target thread that may not yet exist.
+    Mailbox();
+    
     Mailbox(Scheduler&);
 
-    void push(std::unique_ptr<Message>);
-
+    // Attach the given scheduler to this mailbox and begin processing messages
+    // sent to it. The mailbox must be a "holding" mailbox, as created by the
+    // default constructor Mailbox().
+    void open(Scheduler& scheduler_);
     void close();
+
+    bool isOpen() const;
+
+    void push(std::unique_ptr<Message>);
     void receive();
 
     static void maybeReceive(std::weak_ptr<Mailbox>);
 
 private:
-    Scheduler& scheduler;
+    optional<Scheduler*> scheduler;
 
     std::recursive_mutex receivingMutex;
     std::mutex pushingMutex;