From 14b3866ac09c80b8f34d79227d743eabb2da0f2a Mon Sep 17 00:00:00 2001
From: Tom Willemse
Date: Sat, 4 Jun 2022 22:00:27 -0700
Subject: Chapter 26.1, 26.2, 26.3, and 26.4

---
 clox/src/memory.c | 121 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 121 insertions(+)

(limited to 'clox/src/memory.c')

diff --git a/clox/src/memory.c b/clox/src/memory.c
index 1db1c61..7d403d1 100644
--- a/clox/src/memory.c
+++ b/clox/src/memory.c
@@ -1,9 +1,21 @@
 #include <stdlib.h>
 
+#include "compiler.h"
 #include "memory.h"
 #include "vm.h"
 
+#ifdef DEBUG_LOG_GC
+#include "debug.h"
+#include <stdio.h>
+#endif
+
 void *reallocate(void *pointer, size_t oldSize, size_t newSize) {
+  if (newSize > oldSize) {
+#ifdef DEBUG_STRESS_GC
+    collectGarbage();
+#endif
+  }
+
   if (newSize == 0) {
     free(pointer);
     return NULL;
@@ -15,7 +27,76 @@ void *reallocate(void *pointer, size_t oldSize, size_t newSize) {
   return result;
 }
 
+void markObject(Obj *object) {
+  if (object == NULL)
+    return;
+  if (object->isMarked)
+    return;
+
+#ifdef DEBUG_LOG_GC
+  printf("%p mark ", (void *)object);
+  printValue(OBJ_VAL(object));
+  printf("\n");
+#endif
+  object->isMarked = true;
+
+  if (vm.grayCapacity < vm.grayCount + 1) {
+    vm.grayCapacity = GROW_CAPACITY(vm.grayCapacity);
+    vm.grayStack =
+        (Obj **)realloc(vm.grayStack, sizeof(Obj *) * vm.grayCapacity);
+    if (vm.grayStack == NULL)
+      exit(1);
+  }
+
+  vm.grayStack[vm.grayCount++] = object;
+}
+
+void markValue(Value value) {
+  if (IS_OBJ(value))
+    markObject(AS_OBJ(value));
+}
+
+static void markArray(ValueArray *array) {
+  for (int i = 0; i < array->count; i++) {
+    markValue(array->values[i]);
+  }
+}
+
+static void blackenObject(Obj *object) {
+#ifdef DEBUG_LOG_GC
+  printf("%p blacken ", (void *)object);
+  printValue(OBJ_VAL(object));
+  printf("\n");
+#endif
+  switch (object->type) {
+  case OBJ_CLOSURE: {
+    ObjClosure *closure = (ObjClosure *)object;
+    markObject((Obj *)closure->function);
+    for (int i = 0; i < closure->upvalueCount; i++) {
+      markObject((Obj *)closure->upvalues[i]);
+    }
+    break;
+  }
+  case OBJ_FUNCTION: {
+    ObjFunction *function = (ObjFunction *)object;
+    markObject((Obj *)function->name);
+    markArray(&function->chunk.constants);
+    break;
+  }
+  case OBJ_UPVALUE:
+    markValue(((ObjUpvalue *)object)->closed);
+    break;
+  case OBJ_NATIVE:
+  case OBJ_STRING:
+    break;
+  }
+}
+
 static void freeObject(Obj *object) {
+#ifdef DEBUG_LOG_GC
+  printf("%p free type %d\n", (void *)object, object->type);
+#endif // DEBUG_LOG_GC
+
   switch (object->type) {
   case OBJ_CLOSURE: {
     ObjClosure *closure = (ObjClosure *)object;
@@ -44,6 +125,44 @@ static void freeObject(Obj *object) {
   }
 }
 
+static void markRoots() {
+  for (Value *slot = vm.stack; slot < vm.stackTop; slot++) {
+    markValue(*slot);
+  }
+
+  for (int i = 0; i < vm.frameCount; i++) {
+    markObject((Obj *)vm.frames[i].closure);
+  }
+
+  for (ObjUpvalue *upvalue = vm.openUpvalues; upvalue != NULL;
+       upvalue = upvalue->next) {
+    markObject((Obj *)upvalue);
+  }
+
+  markTable(&vm.globals);
+  markCompilerRoots();
+}
+
+static void traceReferences() {
+  while (vm.grayCount > 0) {
+    Obj *object = vm.grayStack[--vm.grayCount];
+    blackenObject(object);
+  }
+}
+
+void collectGarbage() {
+#ifdef DEBUG_LOG_GC
+  printf("-- gc begin\n");
+#endif
+
+  markRoots();
+  traceReferences();
+
+#ifdef DEBUG_LOG_GC
+  printf("-- gd end\n");
+#endif
+}
+
 void freeObjects() {
   Obj *object = vm.objects;
   while (object != NULL) {
@@ -51,4 +170,6 @@ void freeObjects() {
     freeObject(object);
     object = next;
   }
+
+  free(vm.grayStack);
 }
-- 
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