Chapter 26.5

clox/src/memory.c

@@ -150,6 +150,28 @@ static void traceReferences() {
   }
 }
 
+static void sweep() {
+  Obj *previous = NULL;
+  Obj *object = vm.objects;
+  while (object != NULL) {
+    if (object->isMarked) {
+      object->isMarked = false;
+      previous = object;
+      object = object->next;
+    } else {
+      Obj *unreached = object;
+      object = object->next;
+      if (previous != NULL) {
+        previous->next = object;
+      } else {
+        vm.objects = object;
+      }
+
+      freeObject(unreached);
+    }
+  }
+}
+
 void collectGarbage() {
 #ifdef DEBUG_LOG_GC
   printf("-- gc begin\n");
@@ -157,6 +179,8 @@ void collectGarbage() {
 
   markRoots();
   traceReferences();
+  tableRemoveWhite(&vm.strings);
+  sweep();
 
 #ifdef DEBUG_LOG_GC
   printf("-- gd end\n");

clox/src/table.c

@@ -141,6 +141,15 @@ ObjString *tableFindString(Table *table, const char *chars, int length,
   }
 }
 
+void tableRemoveWhite(Table *table) {
+  for (int i = 0; i < table->capacity; i++) {
+    Entry *entry = &table->entries[i];
+    if (entry->key != NULL && !entry->key->obj.isMarked) {
+      tableDelete(table, entry->key);
+    }
+  }
+}
+
 void markTable(Table *table) {
   for (int i = 0; i < table->capacity; i++) {
     Entry *entry = &table->entries[i];

clox/src/table.h

@@ -23,6 +23,7 @@ bool tableDelete(Table *table, ObjString *key);
 void tableAddAll(Table *from, Table *to);
 ObjString *tableFindString(Table *talbe, const char *chars, int length,
                            uint32_t hash);
+void tableRemoveWhite(Table *table);
 void markTable(Table *table);
 
 #endif