Cleaning up.
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1b7c81e469
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1bfe867634
238
src/collector.c
238
src/collector.c
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#include <stdio.h>
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#include <stdlib.h>
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#define MAX_STACK 256
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#define MAX_BARRIER 8
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typedef enum {
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OBJ_INT,
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OBJ_PAIR
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} ObjectType;
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typedef struct sObject {
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unsigned char marked;
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struct sObject* next;
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ObjectType type;
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union {
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int value;
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struct {
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struct sObject* head;
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struct sObject* tail;
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};
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};
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} Object;
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typedef struct {
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Object* stack[MAX_STACK];
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Object* root;
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int stackSize;
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int numObjects;
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int maxObjects;
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} VM;
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void assert(int condition, const char* message) {
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if (!condition) {
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printf("%s\n", message);
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exit(1);
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}
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}
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VM* newVM() {
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VM* vm = malloc(sizeof(VM));
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vm->stackSize = 0;
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vm->numObjects = 0;
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vm->maxObjects = MAX_BARRIER;
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return vm;
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}
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void push(VM* vm, Object* value) {
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assert(vm->stackSize < MAX_STACK, "Stack overflow!");
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vm->stack[vm->stackSize++] = value;
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}
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Object* pop(VM* vm) {
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assert(vm->stackSize > 0, "Stack underflow!");
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return vm->stack[--(vm->stackSize)];
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}
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void mark(Object* object) {
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if (object->marked) {
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return;
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}
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object->marked = 1;
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if (object->type == OBJ_PAIR) {
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mark(object->head);
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mark(object->tail);
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}
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}
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void markAll(VM* vm) {
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for(int i = 0; i < vm->stackSize; i++) {
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mark(vm->stack[i]);
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}
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}
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void sweep(VM* vm) {
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Object** object = &vm->root;
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while (*object) {
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if (!(*object)->marked) {
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Object* unreached = *object;
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*object = unreached->next;
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vm->numObjects--;
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free(unreached);
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} else {
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(*object)->marked = 0;
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object = &(*object)->next;
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}
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}
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}
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void gc(VM* vm) {
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int numObjects = vm->numObjects;
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markAll(vm);
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sweep(vm);
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vm->maxObjects = vm->numObjects * 2;
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printf("Collected %d objects, %d remaining.\n", numObjects - vm->numObjects,
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vm->numObjects);
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}
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Object *newObject(VM* vm, ObjectType type) {
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if (vm->numObjects == vm->maxObjects) {
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gc(vm);
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}
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Object* object = malloc(sizeof(Object));
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object->marked = 0;
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object->type = type;
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object->next = vm->root;
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vm->root = object;
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vm->numObjects++;
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return object;
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}
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Object* pushInt(VM* vm, int value) {
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Object* object = newObject(vm, OBJ_INT);
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object->value = value;
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push(vm, object);
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return object;
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}
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Object* pushPair(VM* vm) {
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Object* object = newObject(vm, OBJ_PAIR);
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object->head = pop(vm);
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object->tail = pop(vm);
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push(vm, object);
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return object;
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}
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void freeVM(VM *vm) {
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vm->stackSize = 0;
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gc(vm);
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free(vm);
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}
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void objectPrint(Object* object) {
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switch(object->type) {
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case OBJ_INT:
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printf("%d\n", object->value);
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break;
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case OBJ_PAIR:
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printf("(");
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objectPrint(object->head);
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printf(", ");
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objectPrint(object->tail);
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printf(")");
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break;
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}
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}
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void test1() {
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printf("Test 1: Objects on stack are preserved.\n");
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VM* vm = newVM();
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pushInt(vm, 1);
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pushInt(vm, 2);
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gc(vm);
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assert(vm->numObjects == 2, "Should have preserved objects.");
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freeVM(vm);
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}
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void test2() {
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printf("Test 2: Unreached objects are collected.\n");
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VM* vm = newVM();
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pushInt(vm, 1);
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pushInt(vm, 2);
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pop(vm);
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pop(vm);
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gc(vm);
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assert(vm->numObjects == 0, "Should have collected objects.");
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freeVM(vm);
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}
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void test3() {
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printf("Test 3: Reach nested objects.\n");
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VM* vm = newVM();
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pushInt(vm, 1);
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pushInt(vm, 2);
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pushPair(vm);
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pushInt(vm, 3);
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pushInt(vm, 4);
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pushPair(vm);
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pushPair(vm);
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gc(vm);
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assert(vm->numObjects == 7, "Should have reached objects.");
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freeVM(vm);
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}
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void test4() {
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printf("Test 4: Handle cycles.\n");
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VM* vm = newVM();
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pushInt(vm, 1);
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pushInt(vm, 2);
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Object* a = pushPair(vm);
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pushInt(vm, 3);
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pushInt(vm, 4);
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Object* b = pushPair(vm);
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/* Set up a cycle, and also make 2 and 4 unreachable and collectible. */
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a->tail = b;
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b->tail = a;
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gc(vm);
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assert(vm->numObjects == 4, "Should have collected objects.");
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freeVM(vm);
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}
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void perfTest() {
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printf("Performance Test.\n");
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VM* vm = newVM();
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for (int i = 0; i < 1000; i++) {
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for (int j = 0; j < 20; j++) {
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pushInt(vm, i);
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}
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for (int k = 0; k < 20; k++) {
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pop(vm);
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}
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}
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freeVM(vm);
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}
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int main(int argc, const char * argv[]) {
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test1();
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test2();
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test3();
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test4();
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perfTest();
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return 0;
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}
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