From f55860b83e4503452d1bfa957588e3e9812593e1 Mon Sep 17 00:00:00 2001
From: Michael Sippel <m.sippel@hzdr.de>
Date: Thu, 7 Dec 2023 03:10:31 +0100
Subject: [PATCH] GraphProperty: replace redundant `task` member with address
 calculation through offsetof

---
 redGrapes/task/property/graph.cpp | 19 +++++++++++----
 redGrapes/task/property/graph.hpp | 40 +++++++++++++------------------
 redGrapes/task/task_space.cpp     |  1 -
 3 files changed, 31 insertions(+), 29 deletions(-)

diff --git a/redGrapes/task/property/graph.cpp b/redGrapes/task/property/graph.cpp
index e72714f5..e9197c2e 100644
--- a/redGrapes/task/property/graph.cpp
+++ b/redGrapes/task/property/graph.cpp
@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
+#include <cstddef>
 #include <memory>
 #include <unordered_set>
 
@@ -19,6 +20,14 @@
 namespace redGrapes
 {
 
+Task * GraphProperty::get_task()
+{       
+    /* NOTE: this offsetof gives works because we know that `space` is
+     * the first member that is derived from `GraphProperty`
+     */
+    return (Task*) ( (uintptr_t)this - offsetof(Task, space) );
+}
+
 /*! create a new (external) event which precedes the tasks post-event
  */
 scheduler::EventPtr GraphProperty::make_event()
@@ -37,7 +46,7 @@ scheduler::EventPtr GraphProperty::make_event()
 void GraphProperty::init_graph()
 {
     TRACE_EVENT("Graph", "init_graph");
-    for( auto r = this->task->unique_resources.rbegin(); r != this->task->unique_resources.rend(); ++r )
+    for( auto r = get_task()->unique_resources.rbegin(); r != get_task()->unique_resources.rend(); ++r )
     {
         if( r->task_entry != r->resource->users.rend() )
         {
@@ -65,7 +74,7 @@ void GraphProperty::init_graph()
 
                 if(
                    preceding_task->space == this->space &&
-                   this->space->is_serial( *preceding_task, *this->task )
+                   this->space->is_serial( *preceding_task, *get_task() )
                 )
                 {
                     add_dependency( *preceding_task );
@@ -87,7 +96,7 @@ void GraphProperty::init_graph()
 void GraphProperty::delete_from_resources()
 {
     TRACE_EVENT("Graph", "delete_from_resources");
-    for( auto r = this->task->unique_resources.rbegin(); r != this->task->unique_resources.rend(); ++r )
+    for( auto r = get_task()->unique_resources.rbegin(); r != get_task()->unique_resources.rend(); ++r )
     {
         // TODO: can this lock be avoided?
         //   corresponding lock to init_graph()
@@ -105,7 +114,7 @@ void GraphProperty::add_dependency( Task & preceding_task )
 
     // scheduling graph
     auto preceding_event =
-        SingletonContext::get().scheduler->task_dependency_type(preceding_task, *this->task)
+        SingletonContext::get().scheduler->task_dependency_type(preceding_task, *get_task())
         ? preceding_task->get_pre_event() : preceding_task->get_post_event();
 
     if( ! preceding_event->is_reached() )
@@ -122,7 +131,7 @@ void GraphProperty::update_graph( )
         scheduler::EventPtr follower = *it;
         if( follower.task )
         {
-            if( ! space->is_serial(*this->task, *follower.task) )
+            if( ! space->is_serial(*get_task(), *follower.task) )
             {
                 // remove dependency
                 //follower.task->in_edges.erase(std::find(std::begin(follower.task->in_edges), std::end(follower.task->in_edges), this));
diff --git a/redGrapes/task/property/graph.hpp b/redGrapes/task/property/graph.hpp
index c11447ec..135b0884 100644
--- a/redGrapes/task/property/graph.hpp
+++ b/redGrapes/task/property/graph.hpp
@@ -48,54 +48,48 @@ struct TaskSpace;
  */
 struct GraphProperty
 {
-    Task & operator*()
-    {
-        return *task;
-    }
-    Task * operator->()
-    {
-        return task;
-    }
-
     //! task space that contains this task, must not be null
     memory::Refcounted< TaskSpace, TaskSpaceDeleter >::Guard space;
 
     //! task space for children, may be null
     memory::Refcounted< TaskSpace, TaskSpaceDeleter >::Guard children;
 
-        
-/*
-    // in edges dont need a mutex because they are initialized
-    // once by `init_dependencies()` and only read afterwards.
-    // expired pointers (null) must be ignored
-    std::vector<Task*> in_edges;
-    */
-
+    //! events of the scheduling-graph
     scheduler::Event pre_event;
     scheduler::Event post_event;
     scheduler::Event result_set_event;
     scheduler::Event result_get_event;
 
-    Task * task;
-
     //! number of parents
     uint8_t scope_depth;
 
+    Task * get_task();
+
+    inline Task & operator*()
+    {
+        return *get_task();
+    }
+
+    inline Task * operator->()
+    {
+        return get_task();
+    }
+
     inline scheduler::EventPtr get_pre_event()
     {
-        return scheduler::EventPtr { nullptr, this->task, scheduler::T_EVT_PRE };
+        return scheduler::EventPtr { nullptr, this->get_task(), scheduler::T_EVT_PRE };
     }
     inline scheduler::EventPtr get_post_event()
     {
-        return scheduler::EventPtr { nullptr, this->task, scheduler::T_EVT_POST };
+        return scheduler::EventPtr { nullptr, this->get_task(), scheduler::T_EVT_POST };
     }
     inline scheduler::EventPtr get_result_set_event()
     {
-        return scheduler::EventPtr { nullptr, this->task, scheduler::T_EVT_RES_SET };
+        return scheduler::EventPtr { nullptr, this->get_task(), scheduler::T_EVT_RES_SET };
     }
     inline scheduler::EventPtr get_result_get_event()
     {
-        return scheduler::EventPtr { nullptr, this->task, scheduler::T_EVT_RES_GET };
+        return scheduler::EventPtr { nullptr, this->get_task(), scheduler::T_EVT_RES_GET };
     }
 
     inline bool is_ready()
diff --git a/redGrapes/task/task_space.cpp b/redGrapes/task/task_space.cpp
index 83cb4036..98c49a5f 100644
--- a/redGrapes/task/task_space.cpp
+++ b/redGrapes/task/task_space.cpp
@@ -74,7 +74,6 @@ namespace redGrapes
     {
         TRACE_EVENT("TaskSpace", "submit()");
         task->space.acquire( this );
-        task->task = task;
 
         ++ task_count;