From 450dda40a8defbb8516ac97b6836125cba34122e Mon Sep 17 00:00:00 2001
From: xFrednet <xFrednet@gmail.com>
Date: Fri, 18 Oct 2024 14:37:24 +0200
Subject: [PATCH] Cown: Reifing cown objects

---
 src/rt/core.h               | 49 +++++++++++++++++++++++++++++++++++++
 src/rt/objects/dyn_object.h | 18 +++++++++++---
 src/rt/rt.cc                | 27 ++++++++++++++++++++
 src/rt/rt.h                 |  1 +
 4 files changed, 91 insertions(+), 4 deletions(-)

diff --git a/src/rt/core.h b/src/rt/core.h
index e4acfc0..c4f1e52 100644
--- a/src/rt/core.h
+++ b/src/rt/core.h
@@ -174,6 +174,54 @@ namespace rt::core
     }
   };
 
+  // The prototype object for cown
+  inline PrototypeObject* cownPrototypeObject()
+  {
+    static PrototypeObject* proto = new PrototypeObject("Cown");
+    return proto;
+  }
+
+  class CownObject : public objects::DynObject
+  {
+    // For now always false, but might be needed later if we want to simulate
+    // concurrency.
+    bool aquired = false;
+
+  public:
+    CownObject(objects::DynObject* region)
+    : objects::DynObject(cownPrototypeObject()),
+    {
+      // FIXME: Add once regions are reified
+      // assert(
+      //   region->get_prototype() == regionPrototype() &&
+      //   "Cowns can only store regions");
+      //
+      // FIXME: Also check that the region has a LRC == 1, with 1
+      // being the reference passed into this constructor
+      this->set("region", region);
+    }
+
+    bool is_aquired()
+    {
+      return aquired;
+    }
+
+    std::string get_name()
+    {
+      return "<cown>";
+    }
+
+    objects::DynObject* is_primitive()
+    {
+      return this;
+    }
+
+    bool is_cown() override
+    {
+      return false;
+    }
+  };
+
   inline std::set<objects::DynObject*>* globals()
   {
     static std::set<objects::DynObject*>* globals =
@@ -185,6 +233,7 @@ namespace rt::core
         keyIterPrototypeObject(),
         trueObject(),
         falseObject(),
+        cownPrototypeObject(),
       };
     return globals;
   }
diff --git a/src/rt/objects/dyn_object.h b/src/rt/objects/dyn_object.h
index b12ee5d..a5285e9 100644
--- a/src/rt/objects/dyn_object.h
+++ b/src/rt/objects/dyn_object.h
@@ -27,8 +27,10 @@ namespace rt::objects
   {
     friend class Reference;
     friend objects::DynObject* rt::make_iter(objects::DynObject* obj);
-    friend void
-    rt::ui::mermaid(std::vector<objects::DynObject*>& roots, std::ostream& out, std::vector<objects::DynObject*>* taint);
+    friend void rt::ui::mermaid(
+      std::vector<objects::DynObject*>& roots,
+      std::ostream& out,
+      std::vector<objects::DynObject*>* taint);
     friend void destruct(DynObject* obj);
     friend void dealloc(DynObject* obj);
     template<typename Pre, typename Post>
@@ -241,7 +243,8 @@ namespace rt::objects
           get_region(obj)->objects.erase(obj);
         }
         obj->region.set_tag(ImmutableTag);
-        return true;
+
+        return !obj->is_cown();
       });
     }
 
@@ -250,6 +253,11 @@ namespace rt::objects
       return region.get_tag() == ImmutableTag;
     }
 
+    virtual bool is_cown()
+    {
+      return false;
+    }
+
     [[nodiscard]] DynObject* get(std::string name)
     {
       auto result = fields.find(name);
@@ -270,7 +278,7 @@ namespace rt::objects
 
     [[nodiscard]] DynObject* set(std::string name, DynObject* value)
     {
-      if (is_immutable())
+      if (is_immutable() && this->is_cown())
       {
         ui::error("Cannot mutate immutable object");
       }
@@ -282,6 +290,7 @@ namespace rt::objects
     // The caller must provide an rc for value.
     [[nodiscard]] DynObject* set_prototype(DynObject* value)
     {
+      // No need to check for a cown, since cowns already have a set prototype
       if (is_immutable())
       {
         ui::error("Cannot mutate immutable object");
@@ -331,6 +340,7 @@ namespace rt::objects
     static void
     move_reference(DynObject* src, DynObject* dst, DynObject* target)
     {
+      // An immutable cown can't be moved to another region
       if (target == nullptr || target->is_immutable())
         return;
 
diff --git a/src/rt/rt.cc b/src/rt/rt.cc
index 6c46386..a24ee65 100644
--- a/src/rt/rt.cc
+++ b/src/rt/rt.cc
@@ -34,11 +34,18 @@ namespace rt
     return new core::FrameObject(parent);
   }
 
+  objects::DynObject* make_cown(objects::DynObject* region)
+  {
+    return new core::CownObject(region);
+  }
+
   thread_local objects::RegionPointer objects::DynObject::local_region =
     new Region();
 
   void freeze(objects::DynObject* obj)
   {
+    // Cown specific handling of the freeze operation is handled by the
+    // `freeze()` implementation of the object
     obj->freeze();
   }
 
@@ -49,6 +56,15 @@ namespace rt
 
   objects::DynObject* get(objects::DynObject* obj, std::string key)
   {
+    if (obj->get_prototype() == core::cownPrototypeObject())
+    {
+      core::CownObject* cown = reinterpret_cast<core::CownObject*>(obj);
+      if (!cown->is_aquired())
+      {
+        ui::error(
+          "the cown needs to be aquired, before its data can be accessed");
+      }
+    }
     return obj->get(key);
   }
 
@@ -72,6 +88,17 @@ namespace rt
   objects::DynObject*
   set(objects::DynObject* obj, std::string key, objects::DynObject* value)
   {
+    if (obj->get_prototype() == core::cownPrototypeObject())
+    {
+      core::CownObject* cown = reinterpret_cast<core::CownObject*>(obj);
+      if (!cown->is_aquired())
+      {
+        // Overwriting data can change the RC and then call destructors of the
+        // type this action therefore requires the cown to be aquired
+        ui::error("the cown needs to be aquired, before its data can modified");
+      }
+    }
+
     return obj->set(key, value);
   }
 
diff --git a/src/rt/rt.h b/src/rt/rt.h
index 4fc2046..9eea970 100644
--- a/src/rt/rt.h
+++ b/src/rt/rt.h
@@ -15,6 +15,7 @@ namespace rt
   objects::DynObject* make_str(std::string str_value);
   objects::DynObject* make_object();
   objects::DynObject* make_frame(objects::DynObject* parent);
+  objects::DynObject* make_cown(objects::DynObject* region);
 
   void freeze(objects::DynObject* obj);
   void create_region(objects::DynObject* objects);