From 8568ebe52b3fa43e935825cf88e43d104af80aa6 Mon Sep 17 00:00:00 2001
From: Andrew Scott <git@andyscott.me>
Date: Tue, 20 Aug 2024 13:18:35 -0400
Subject: [PATCH] VM: define initial GC threshold and check malloc for NULL

---
 vm.c | 26 +++++++++++++++++++++-----
 vm.h |  1 +
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/vm.c b/vm.c
index 68d37b7..d90dad7 100644
--- a/vm.c
+++ b/vm.c
@@ -1,14 +1,14 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-#include "vm.h"
 #include "gc.h"
+#include "vm.h"
 
 struct virtualMachine *initVM() {
   struct virtualMachine *vm = malloc(sizeof(struct virtualMachine));
   vm->stackSize = 0;
   vm->refCount = 0;
-  vm->refMax = STACK_MAX / 2;
+  vm->refMax = GC_THRESHOLD;
   vm->head = NULL;
   return vm;
 }
@@ -23,8 +23,7 @@ void push(struct virtualMachine *vm, struct garbageObject *value) {
 
 struct garbageObject *pop(struct virtualMachine *vm) {
   if (vm->stackSize < 0) {
-    fprintf(stderr,
-            "ERROR: pop(): Stack size cannot be negative!");
+    fprintf(stderr, "ERROR: pop(): Stack size cannot be negative!");
     return NULL;
   }
 
@@ -33,9 +32,17 @@ struct garbageObject *pop(struct virtualMachine *vm) {
 
 struct garbageObject *initGarbage(struct virtualMachine *vm,
                                   enum garbageData type) {
-  if (vm->refCount == vm->refMax) collect(vm);
+
+  if (vm->refCount >= vm->refMax) {
+    collect(vm);
+  }
 
   struct garbageObject *obj = malloc(sizeof(struct garbageObject));
+  if (obj == NULL) {
+    fprintf(stderr, "initGarbage(): Allocation failure!");
+    return obj;
+  }
+
   obj->type = type;
   obj->mark = 0;
   obj->next = vm->head;
@@ -46,12 +53,21 @@ struct garbageObject *initGarbage(struct virtualMachine *vm,
 
 void pushInt(struct virtualMachine *vm, int value) {
   struct garbageObject *obj = initGarbage(vm, GARBAGE_INT);
+  if (obj == NULL) {
+    fprintf(stderr, "pushInt(): Unable to create GARBAGE_INT - out of memory?");
+  }
+
   obj->value = value;
   push(vm, obj);
 }
 
 struct garbageObject *pushPair(struct virtualMachine *vm) {
   struct garbageObject *obj = initGarbage(vm, GARBAGE_PAIR);
+  if (obj == NULL) {
+    fprintf(stderr,
+            "pushPair(): Unable to create GARBAGE_PAIR - out of memory?");
+  }
+
   obj->tail = pop(vm);
   obj->head = pop(vm);
 
diff --git a/vm.h b/vm.h
index 90803e4..8e7f0bc 100644
--- a/vm.h
+++ b/vm.h
@@ -2,6 +2,7 @@
 #define VM_H
 
 #define STACK_MAX 1024
+#define GC_THRESHOLD 256
 
 // Primitive types for garbage collection
 enum garbageData {