From 3860d0ec4f04ed1307631574d96cf2634bdacb2f Mon Sep 17 00:00:00 2001
From: valtermiari <valter@miari.se>
Date: Mon, 20 Feb 2023 14:34:57 +0100
Subject: [PATCH] Tweaked sweeping, test with detached pointers

---
 src/GC/lib/heap.cpp     | 42 +++++++++++++++++++++--------------------
 src/GC/tests/h_test.cpp | 32 ++++++++++++++++++-------------
 src/GC/todo.md          |  1 +
 3 files changed, 42 insertions(+), 33 deletions(-)

diff --git a/src/GC/lib/heap.cpp b/src/GC/lib/heap.cpp
index d13cec6..f2d04ee 100644
--- a/src/GC/lib/heap.cpp
+++ b/src/GC/lib/heap.cpp
@@ -192,49 +192,51 @@ namespace GC {
     }
   }
 
-  // Not optimal for now, it doesn't have to loop over all objects
-  // but mark needs some refinements before this can be optimised
+  /**
+   * Sweeps the heap, unmarks the marked chunks for the next cycle,
+   * adds the unmarked nodes to the vector of freed chunks; to be freed.
+   * 
+   * @param *heap The heap to oporate on.
+  */
   void Heap::sweep(Heap *heap) {
     for (auto it = heap->m_allocated_chunks.begin(); it != heap->m_allocated_chunks.end();) {
         auto chunk = *it;
-        if (!chunk->marked) {
+
+        // Unmark the marked chunks for the next iteration.
+        if (chunk->marked) {
+            chunk->marked = false;
+            ++it;
+        }
+        else {
+            // Add the unmarked chunks to freed chunks and remove from
+            // the list of allocated chunks 
             heap->m_freed_chunks.push_back(chunk);
             it = heap->m_allocated_chunks.erase(it);
         }
-        else { 
-            ++it;
-        }
     }
   }
 
-  // TODO: return the worklist filtered on mark = true
   // This assumes that there are no chains of pointers, will be fixed later on
   void Heap::mark(uintptr_t *start, const uintptr_t *end, vector<Chunk*> worklist) {
     for (; start > end; start--) { // to find adresses thats in the worklist
       if (*start % 8 == 0) { // all pointers must be aligned as double words
         for (auto it = worklist.begin(); it != worklist.end();) {
-        //for (size_t i = 0; i < worklist.size(); i++) { // fix this
-          //auto chunk = worklist.at(i);
           auto chunk = *it;
           uintptr_t c_start = reinterpret_cast<uintptr_t>(chunk->start);
           uintptr_t c_end = reinterpret_cast<uintptr_t>(chunk->start + chunk->size);
-          if (c_start <= *start && *start < c_end) {
-            uintptr_t c_start = reinterpret_cast<uintptr_t>(chunk->start);
-            if (!chunk->marked) {
+          // Check if the stack pointer aligns with the chunk
+          if ((c_start <= *start && *start < c_end) && chunk != nullptr) {
+          cout << "Chunk start:\t" << c_start << endl;
+          cout << "Chunk end:\t" << c_end << endl;           
+          if (!chunk->marked) {
               chunk->marked = true;
-              //worklist.erase(worklist.begin() + i);
               it = worklist.erase(it);
-              //auto new_stack_start = reinterpret_cast<uintptr_t *>(start);
-              //mark(new_stack_start, end, worklist); //
-              //return;
             }
-            else {
+            else 
               ++it;
-            }
           }
-          else {
+          else
             ++it;
-          }
         }
       }
     }
diff --git a/src/GC/tests/h_test.cpp b/src/GC/tests/h_test.cpp
index 65f51d6..cd93f7e 100644
--- a/src/GC/tests/h_test.cpp
+++ b/src/GC/tests/h_test.cpp
@@ -9,36 +9,42 @@ GC::Heap *gc = GC::Heap::the();
     *dst = local;
 } */
 
+void create_array(size_t size) {
+    int *arr = static_cast<int *>(gc->alloc(sizeof(int) * size));
+}
+
+void detach_pointer(long **ptr) {
+    long dummy = 10; // dummy value
+    long *dummy_ptr = &dummy;
+    *ptr = dummy_ptr;
+    std::cout << "Dummy pointer: \t" << dummy_ptr << std::endl;
+    std::cout << "Detach pointer result:\t" << ptr << std::endl;
+}
+
 void init() {
 
     auto stack_start = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
-    //auto stack_end = stack_start - 40;
     std::cout << "Stack start from init:\t" << stack_start << std::endl;
-    //std::cout << "Imaginary stack end:\t" << stack_end << std::endl;
     int *arr = static_cast<int *>(gc->alloc(sizeof(int) * 100));
+    create_array(100);
+    //arr = create_array(100);
     //std::cout << "Arr_ptr" << std::hex << arr << "\n\n\n" << std::endl;
     for (int i = 0; i < (sizeof(int) * 100); i++) {
         arr[i] = i;
     }
-    for (int i = 0; i < (sizeof(int) * 20); i++) {
-        gc->alloc(sizeof(int));
-    }
     std::cout << "Pointer for arr:\t" << &arr << std::endl;
-    long a = 20;
     long *l = static_cast<long *>(gc->alloc(sizeof(long)));
-    std::cout << "Pointer for l:\t\t" << &l << std::endl;
-    int *i = static_cast<int *>(gc->alloc(sizeof(int)));
-    std::cout << "Pointer for i:\t\t" << &i << std::endl;
-    //l = &a;
-    //*l = 20;
+    std::cout << "l points to:\t\t" << l << std::endl;
+    detach_pointer(&l);
+    std::cout << "l points to:\t\t" << l << std::endl;
+    // l still gets marked, which is not supposed to happen
 }
 
 int main() {
     auto stack_start = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
     std::cout << "Stack start from main:\t" << stack_start << std::endl;
     init();
-    gc->collect(MARK | SWEEP); // some bug in free (vector out of range)
+    gc->collect(MARK); // some bug in free (vector out of range)
     gc->print_contents();
-    //delete gc;
     return 0;
 }
\ No newline at end of file
diff --git a/src/GC/todo.md b/src/GC/todo.md
index 009ab51..f1e60a2 100644
--- a/src/GC/todo.md
+++ b/src/GC/todo.md
@@ -8,6 +8,7 @@ Goal for next week (24/2):
 ## GC TODO:
 - Merge to main branch
 - Fix singleton references
+- Think about how we want to determine if some object is a pointer or not, probably will have to discuss that with Samuel. Since it is not ideal to determine in the GC if an object is a pointer or not. It should preferably be done in a previous stage.
 
 ## Tests TODO
 ### Library linking