janet/gc.c

#include "datatypes.h"
#include "gc.h"
#include "vm.h"
#include "util.h"

/* The metadata header associated with an allocated block of memory */
#define gc_header(mem) ((GCMemoryHeader *)(mem) - 1)

/* Memory header struct. Node of a linked list of memory blocks. */
typedef struct GCMemoryHeader GCMemoryHeader;
struct GCMemoryHeader {
    GCMemoryHeader * next;
    uint32_t color : 1;
};

/* Helper to mark function environments */
static void gst_mark_funcenv(Gst *vm, GstFuncEnv *env) {
    if (gc_header(env)->color != vm->black) {
        GstValue temp;
        gc_header(env)->color = vm->black;
        if (env->thread) {
            temp.type = GST_THREAD;
            temp.data.thread = env->thread;
            gst_mark(vm, &temp);
        }
        if (env->values) {
            uint32_t count = env->stackOffset;
            uint32_t i;
            gc_header(env->values)->color = vm->black;
            for (i = 0; i < count; ++i)
                gst_mark(vm, env->values + i);
        }
    }
}

/* GC helper to mark a FuncDef */
static void gst_mark_funcdef(Gst *vm, GstFuncDef *def) {
    if (gc_header(def)->color != vm->black) {
        gc_header(def)->color = vm->black;
        gc_header(def->byteCode)->color = vm->black;
        uint32_t count, i;
        if (def->literals) {
            count = def->literalsLen;
            gc_header(def->literals)->color = vm->black;
            for (i = 0; i < count; ++i) {
                /* If the literal is a NIL type, it actually
                 * contains a FuncDef */
               	if (def->literals[i].type == GST_NIL) {
					gst_mark_funcdef(vm, (GstFuncDef *) def->literals[i].data.pointer);
               	} else {
                    gst_mark(vm, def->literals + i);
               	}
            }
        }
    }
}

/* Helper to mark a stack frame. Returns the next frame. */
static GstStackFrame *gst_mark_stackframe(Gst *vm, GstStackFrame *frame) {
    uint32_t i;
    GstValue *stack = (GstValue *)frame + GST_FRAME_SIZE;
    gst_mark(vm, &frame->callee);
    if (frame->env)
        gst_mark_funcenv(vm, frame->env);
    for (i = 0; i < frame->size; ++i)
        gst_mark(vm, stack + i);
    return (GstStackFrame *)(stack + frame->size);
}

/* Mark allocated memory associated with a value. This is
 * the main function for doing the garbage collection mark phase. */
void gst_mark(Gst *vm, GstValue *x) {
    switch (x->type) {
        case GST_NIL:
        case GST_BOOLEAN:
        case GST_NUMBER:
        case GST_CFUNCTION:
            break;

        case GST_STRING:
            gc_header(gst_string_raw(x->data.string))->color = vm->black;
            break;

        case GST_BYTEBUFFER:
            gc_header(x->data.buffer)->color = vm->black;
            gc_header(x->data.buffer->data)->color = vm->black;
            break;

        case GST_ARRAY:
            if (gc_header(x->data.array)->color != vm->black) {
                uint32_t i, count;
                count = x->data.array->count;
                gc_header(x->data.array)->color = vm->black;
                gc_header(x->data.array->data)->color = vm->black;
                for (i = 0; i < count; ++i)
                    gst_mark(vm, x->data.array->data + i);
            }
            break;

        case GST_THREAD:
            if (gc_header(x->data.thread)->color != vm->black) {
                GstThread *thread = x->data.thread;
                GstStackFrame *frame = (GstStackFrame *)thread->data;
                GstStackFrame *end = (GstStackFrame *)(thread->data +
                    thread->count - GST_FRAME_SIZE);
                gc_header(thread)->color = vm->black;
                gc_header(thread->data)->color = vm->black;
                while (frame <= end)
                    frame = gst_mark_stackframe(vm, frame);
            }
            break;

        case GST_FUNCTION:
            if (gc_header(x->data.function)->color != vm->black) {
                GstFunction *f = x->data.function;
                gc_header(f)->color = vm->black;
                gst_mark_funcdef(vm, f->def);
                if (f->env)
                    gst_mark_funcenv(vm, f->env);
                if (f->parent) {
                    GstValue temp;
                    temp.type = GST_FUNCTION;
                    temp.data.function = f->parent;
                    gst_mark(vm, &temp);
                }
            }
            break;

        case GST_OBJECT:
            if (gc_header(x->data.object)->color != vm->black) {
                uint32_t i;
                GstBucket *bucket;
                gc_header(x->data.object)->color = vm->black;
                gc_header(x->data.object->buckets)->color = vm->black;
                for (i = 0; i < x->data.object->capacity; ++i) {
					bucket = x->data.object->buckets[i];
					while (bucket) {
    					gc_header(bucket)->color = vm->black;
						gst_mark(vm, &bucket->key);
						gst_mark(vm, &bucket->value);
						bucket = bucket->next;
					}
                }
            }
            break;
    }
}

/* Iterate over all allocated memory, and free memory that is not
 * marked as reachable. Flip the gc color flag for next sweep. */
void gst_sweep(Gst *vm) {
    GCMemoryHeader *previous = NULL;
    GCMemoryHeader *current = vm->blocks;
    GCMemoryHeader *next;
    while (current) {
        next = current->next;
        if (current->color != vm->black) {
            if (previous) {
                previous->next = next;
            } else {
                vm->blocks = next;
            }
            gst_raw_free(current);
        } else {
            previous = current;
        }
        current = next;
    }
    /* Rotate flag */
    vm->black = !vm->black;
}

/* Prepare a memory block */
static void *gst_alloc_prepare(Gst *vm, char *rawBlock, uint32_t size) {
    GCMemoryHeader *mdata;
    if (rawBlock == NULL) {
        gst_crash(vm, "out of memory");
    }
    vm->nextCollection += size;
    mdata = (GCMemoryHeader *)rawBlock;
    mdata->next = vm->blocks;
    vm->blocks = mdata;
    mdata->color = !vm->black;
    return rawBlock + sizeof(GCMemoryHeader);
}

/* Allocate some memory that is tracked for garbage collection */
void *gst_alloc(Gst *vm, uint32_t size) {
    uint32_t totalSize = size + sizeof(GCMemoryHeader);
    return gst_alloc_prepare(vm, gst_raw_alloc(totalSize), totalSize);
}

/* Allocate some zeroed memory that is tracked for garbage collection */
void *gst_zalloc(Gst *vm, uint32_t size) {
    uint32_t totalSize = size + sizeof(GCMemoryHeader);
    return gst_alloc_prepare(vm, gst_raw_calloc(1, totalSize), totalSize);
}

/* Run garbage collection */
void gst_collect(Gst *vm) {
    /* Thread can be null */
    if (vm->thread) {
        GstValue thread;
        thread.type = GST_THREAD;
        thread.data.thread = vm->thread;
        gst_mark(vm, &thread);
    }
    gst_mark(vm, &vm->ret);
    gst_mark(vm, &vm->error);
    gst_sweep(vm);
    vm->nextCollection = 0;
}

/* Run garbage collection if needed */
void gst_maybe_collect(Gst *vm) {
    if (vm->nextCollection >= vm->memoryInterval)
        gst_collect(vm);
}

/* Free all allocated memory */
void gst_clear_memory(Gst *vm) {
    GCMemoryHeader *current = vm->blocks;
    while (current) {
        GCMemoryHeader *next = current->next;
        gst_raw_free(current);
        current = next;
    }
    vm->blocks = NULL;
}