From b21d3adedf338250a25d84a124f93cea4b593f74 Mon Sep 17 00:00:00 2001
From: Jakub Strzebonski <jakub.strzebonski@ng-analytics.com>
Date: Fri, 20 Nov 2020 19:45:24 +0100
Subject: [PATCH] #973: specialize Proxy and ProxyElm for bare handlers

---
 examples/callback/callback_context.cc      | 36 ++--------------------
 src/vt/objgroup/manager.h                  |  8 +++++
 src/vt/objgroup/proxy/proxy_objgroup.h     | 17 ++++++++++
 src/vt/objgroup/proxy/proxy_objgroup_elm.h | 24 +++++++++++++++
 4 files changed, 51 insertions(+), 34 deletions(-)

diff --git a/examples/callback/callback_context.cc b/examples/callback/callback_context.cc
index 0153ef7e9b..f7db10d846 100644
--- a/examples/callback/callback_context.cc
+++ b/examples/callback/callback_context.cc
@@ -96,38 +96,6 @@ static void handler(CallbackMsg* msg) {
 // Some instance of the context
 static MyContext my_global_ctx = {};
 
-namespace {
-
-struct DefaultProxyElem {
-  explicit DefaultProxyElem(vt::NodeType in_node) : node_(in_node) {}
-
-  template <typename MsgT, vt::ActiveTypedFnType<MsgT>* fn, typename... Args>
-  void send(Args&&... args) const {
-    vt::theMsg()->sendMsg<MsgT, fn>(
-      node_, vt::makeMessage<MsgT>(std::forward<Args>(args)...)
-    );
-  }
-
-  private:
-  vt::NodeType node_;
-};
-
-struct DefaultProxy {
-  DefaultProxyElem operator[](vt::NodeType node) const {
-    return DefaultProxyElem{node};
-  }
-
-  static const DefaultProxy& get() {
-    static DefaultProxy const default_proxy;
-    return default_proxy;
-  }
-
-  private:
-  DefaultProxy() = default;
-};
-
-}
-
 int main(int argc, char** argv) {
   vt::initialize(argc, argv);
 
@@ -141,8 +109,8 @@ int main(int argc, char** argv) {
       vt::pipe::LifetimeEnum::Once, &my_global_ctx, callbackFn
     );
 
-    auto const& default_proxy = DefaultProxy::get();
-    default_proxy[1].send<CallbackMsg, handler>(cb);
+    auto const proxy = vt::theObjGroup()->makeCollective();
+    proxy[1].send<CallbackMsg, handler>(cb);
   }
 
   vt::finalize();
diff --git a/src/vt/objgroup/manager.h b/src/vt/objgroup/manager.h
index 0082dcd510..7969da32b7 100644
--- a/src/vt/objgroup/manager.h
+++ b/src/vt/objgroup/manager.h
@@ -109,6 +109,14 @@ struct ObjGroupManager : runtime::component::Component<ObjGroupManager> {
    * communicator
    */
 
+  /**
+   * \brief Construct a special proxy instance that allows sending, broadcasting
+   * and reducing without actual object group.
+   *
+   * \return proxy to the object group
+   */
+  proxy::DefaultProxyType makeCollective() { return proxy::DefaultProxyType{}; }
+
   /**
    * \brief Collectively construct a new object group. Allocates and constructs
    * the object on each node by forwarding constructor arguments.
diff --git a/src/vt/objgroup/proxy/proxy_objgroup.h b/src/vt/objgroup/proxy/proxy_objgroup.h
index 917d038836..6fcebd175f 100644
--- a/src/vt/objgroup/proxy/proxy_objgroup.h
+++ b/src/vt/objgroup/proxy/proxy_objgroup.h
@@ -336,6 +336,23 @@ struct Proxy {
   ObjGroupProxyType proxy_ = no_obj_group; /**< The raw proxy ID bits */
 };
 
+template <>
+struct Proxy<void> {
+  /**
+   * \brief Index the proxy to get the element proxy for a particular node
+   *
+   * \param[in] node the desired node
+   *
+   * \return an indexed proxy to that node
+   */
+  // DefaultProxyElm operator[](NodeType node) const;
+  DefaultProxyElm operator[](NodeType node) const {
+    return DefaultProxyElm{node};
+  }
+};
+
+using DefaultProxyType = Proxy<void>;
+
 }}} /* end namespace vt::objgroup::proxy */
 
 #endif /*INCLUDED_VT_OBJGROUP_PROXY_PROXY_OBJGROUP_H*/
diff --git a/src/vt/objgroup/proxy/proxy_objgroup_elm.h b/src/vt/objgroup/proxy/proxy_objgroup_elm.h
index db840c8590..ae1c9f5ddb 100644
--- a/src/vt/objgroup/proxy/proxy_objgroup_elm.h
+++ b/src/vt/objgroup/proxy/proxy_objgroup_elm.h
@@ -49,6 +49,8 @@
 #include "vt/objgroup/common.h"
 #include "vt/objgroup/proxy/proxy_bits.h"
 #include "vt/objgroup/active_func/active_func.h"
+#include "vt/activefn/activefn.h"
+#include "vt/messaging/active.h"
 #include "vt/messaging/message/smart_ptr.h"
 
 namespace vt { namespace objgroup { namespace proxy {
@@ -179,6 +181,28 @@ struct ProxyElm {
   NodeType node_           = uninitialized_destination; /**< The indexed node */
 };
 
+template <>
+struct ProxyElm<void> {
+  explicit ProxyElm(NodeType in_node) : node_{in_node} {}
+
+  /**
+   * \brief Send a message to the node indexed by this proxy to be
+   * delivered to the local object instance
+   *
+   * \param[in] args args to pass to the message constructor
+   */
+  template <typename MsgT, ActiveTypedFnType<MsgT>* fn, typename... Args>
+  void send(Args&&... args) const {
+    vt::theMsg()->sendMsg<MsgT, fn>(
+      node_, vt::makeMessage<MsgT>(std::forward<Args>(args)...));
+  }
+
+  private:
+  NodeType node_ = uninitialized_destination; /**< The indexed node */
+};
+
+using DefaultProxyElm = ProxyElm<void>;
+
 }}} /* end namespace vt::objgroup::proxy */
 
 #endif /*INCLUDED_VT_OBJGROUP_PROXY_PROXY_OBJGROUP_ELM_H*/