1 files changed, 60 insertions, 0 deletions
diff --git a/include/mbgl/actor/aspiring_actor.hpp b/include/mbgl/actor/aspiring_actor.hpp
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+++ b/include/mbgl/actor/aspiring_actor.hpp
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+#pragma once
+
+#include <mbgl/actor/mailbox.hpp>
+#include <mbgl/actor/message.hpp>
+#include <mbgl/actor/actor_ref.hpp>
+
+#include <memory>
+#include <future>
+#include <type_traits>
+#include <cassert>
+
+namespace mbgl {
+
+template <class Object>
+class EstablishedActor;
+
+template <class Object>
+class Actor;
+
+/*
+    An `AspiringActor<O>` is one half of the pair of types that comprise an actor (see `Actor<O>`),
+    the other half being `EstablishedActor<O>`.  It is responsible for:
+     - ownership of the actor's `Mailbox`
+     - allocating the memory for (but *not* constructing) the target object `O`
+ 
+    Using these two pieces--the mailbox and a stable address for `O`--an `AspiringActor<O>` can
+    accept messages for the target object, or provide `ActorRef<O>`s that do so, before the object
+    has actually been constructed by the corresponding `EstablishedActor<O>`.  (Such messages are
+    queued in the mailbox until after the object is constructed.)
+ 
+    This allows for an `AspiringActor<O>` to be created and safely used by a thread other than the
+    one on which the target object will (eventually) live.
+*/
+template <class Object>
+class AspiringActor {
+public:
+    AspiringActor() : mailbox(std::make_shared<Mailbox>()) {
+        // mailbox starts closed because the `Object` hasn't yet been constructed
+        assert(!mailbox->isOpen());
+    }
+    
+    AspiringActor(const AspiringActor&) = delete;
+    
+    ActorRef<std::decay_t<Object>> self() {
+        return ActorRef<std::decay_t<Object>>(object(), mailbox);
+    }
+    
+private:
+    std::shared_ptr<Mailbox> mailbox;
+    std::aligned_storage_t<sizeof(Object)> objectStorage;
+    
+    Object& object() {
+        return *reinterpret_cast<Object *>(&objectStorage);
+    }
+    
+    friend class EstablishedActor<Object>;
+    friend class Actor<Object>;
+};
+
+} // namespace mbgl