Chapter 26.6

clox/src/memory.c

@@ -9,13 +9,20 @@
 #include <stdio.h>
 #endif
 
+#define GC_HEAP_GROW_FACTOR 2
+
 void *reallocate(void *pointer, size_t oldSize, size_t newSize) {
+  vm.bytesAllocated += newSize - oldSize;
   if (newSize > oldSize) {
 #ifdef DEBUG_STRESS_GC
     collectGarbage();
 #endif
   }
 
+  if (vm.bytesAllocated > vm.nextGC) {
+    collectGarbage();
+  }
+
   if (newSize == 0) {
     free(pointer);
     return NULL;
@@ -175,6 +182,7 @@ static void sweep() {
 void collectGarbage() {
 #ifdef DEBUG_LOG_GC
   printf("-- gc begin\n");
+  size_t before = vm.bytesAllocated;
 #endif
 
   markRoots();
@@ -182,8 +190,12 @@ void collectGarbage() {
   tableRemoveWhite(&vm.strings);
   sweep();
 
+  vm.nextGC = vm.bytesAllocated * GC_HEAP_GROW_FACTOR;
+
 #ifdef DEBUG_LOG_GC
-  printf("-- gd end\n");
+  printf("-- gc end\n");
+  printf("   collected %zu bytes (from %zu to %zu) next at %zu\n",
+         before - vm.bytesAllocated, before, vm.bytesAllocated, vm.nextGC);
 #endif
 }
 

clox/src/vm.c

@@ -55,6 +55,8 @@ static void defineNative(const char *name, NativeFn function) {
 void initVM() {
   resetStack();
   vm.objects = NULL;
+  vm.bytesAllocated = 0;
+  vm.nextGC = 1024 * 1024;
 
   vm.grayCount = 0;
   vm.grayCapacity = 0;

clox/src/vm.h

@@ -24,6 +24,9 @@ typedef struct {
   Table globals;
   Table strings;
   ObjUpvalue *openUpvalues;
+
+  size_t bytesAllocated;
+  size_t nextGC;
   Obj *objects;
   int grayCount;
   int grayCapacity;