Repository: authorNari/minigc
Branch: master
Commit: ac6a38c998d2
Files: 5
Total size: 11.3 KB

Directory structure:
gitextract_otv4rync/

├── MIT-LICENSE
├── Makefile
├── README
├── gc.c
└── gc.h

================================================
FILE CONTENTS
================================================

================================================
FILE: MIT-LICENSE
================================================
Copyright (c) 2010 Narihiro Nakamura

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


================================================
FILE: Makefile
================================================
#
CC = gcc
SRCS = gc.c
BIN = gc

all: clean gc

clean:
	rm -f gc

gc: $(SRCS)
	$(CC) -g -o gc $(SRCS)

gc_debug:
	$(CC) -g -DDO_DEBUG -O0 -o gc $(SRCS)

test: clean gc_debug
	./gc test


================================================
FILE: README
================================================
= mini gc

= Description

This is a simple and minimum GC. The purpose of this project is education.

= Algorithms

* mark and sweep

= Usage

    $ make
    $ ./gc test


================================================
FILE: gc.c
================================================
#ifdef DO_DEBUG
#define DEBUG(exp) (exp)
#else
#define DEBUG(exp)
#endif

#ifndef DO_DEBUG
#define NDEBUG
#endif

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <errno.h>
#include <assert.h>
#include <unistd.h>
#include <setjmp.h>
#include "gc.h"

/* ========================================================================== */
/*  mini_gc_malloc                                                            */
/* ========================================================================== */

typedef struct header {
    size_t flags;
    size_t size;
    struct header *next_free;
} Header;

typedef struct gc_heap {
    Header *slot;
    size_t size;
} GC_Heap;

#define TINY_HEAP_SIZE 0x4000
#define PTRSIZE ((size_t) sizeof(void *))
#define HEADER_SIZE ((size_t) sizeof(Header))
#define HEAP_LIMIT 10000
#define ALIGN(x,a) (((x) + (a - 1)) & ~(a - 1))
#define NEXT_HEADER(x) ((Header *)((size_t)(x+1) + x->size))

/* flags */
#define FL_ALLOC 0x1
#define FL_MARK 0x2
#define FL_SET(x, f) (((Header *)x)->flags |= f)
#define FL_UNSET(x, f) (((Header *)x)->flags &= ~(f))
#define FL_TEST(x, f) (((Header *)x)->flags & f)

static Header *free_list;
static GC_Heap gc_heaps[HEAP_LIMIT];
static size_t gc_heaps_used = 0;


static Header *
add_heap(size_t req_size)
{
    void *p;
    Header *align_p;

    if (gc_heaps_used >= HEAP_LIMIT) {
        fputs("OutOfMemory Error", stderr);
        abort();
    }

    if (req_size < TINY_HEAP_SIZE)
        req_size = TINY_HEAP_SIZE;

    if((p = sbrk(req_size + PTRSIZE + HEADER_SIZE)) == (void *)-1)
        return NULL;

    /* address alignment */
    align_p = gc_heaps[gc_heaps_used].slot = (Header *)ALIGN((size_t)p, PTRSIZE);
    req_size = gc_heaps[gc_heaps_used].size = req_size;
    align_p->size = req_size;
    align_p->next_free = align_p;
    gc_heaps_used++;

    return align_p;
}

static Header *
grow(size_t req_size)
{
    Header *cp, *up;

    if (!(cp = add_heap(req_size)))
        return NULL;

    up = (Header *) cp;
    mini_gc_free((void *)(up+1));
    return free_list;
}

void *
mini_gc_malloc(size_t req_size)
{
    Header *p, *prevp;
    size_t do_gc = 0;

    req_size = ALIGN(req_size, PTRSIZE);

    if (req_size <= 0) {
        return NULL;
    }
    if ((prevp = free_list) == NULL) {
        if (!(p = add_heap(TINY_HEAP_SIZE))) {
            return NULL;
        }
        prevp = free_list = p;
    }
    for (p = prevp->next_free; ; prevp = p, p = p->next_free) {
        if (p->size >= req_size) {
            if (p->size == req_size)
                /* just fit */
                prevp->next_free = p->next_free;
            else {
                /* too big */
                p->size -= (req_size + HEADER_SIZE);
                p = NEXT_HEADER(p);
                p->size = req_size;
            }
            free_list = prevp;
            FL_SET(p, FL_ALLOC);
            return (void *)(p+1);
        }
        if (p == free_list) {
            if (!do_gc) {
                garbage_collect();
                do_gc = 1;
            }
            else if ((p = grow(req_size)) == NULL)
                return NULL;
        }
    }
}

void
mini_gc_free(void *ptr)
{
    Header *target, *hit;

    target = (Header *)ptr - 1;

    /* search join point of target to free_list */
    for (hit = free_list; !(target > hit && target < hit->next_free); hit = hit->next_free)
        /* heap end? And hit(search)? */
        if (hit >= hit->next_free &&
            (target > hit || target < hit->next_free))
            break;

    if (NEXT_HEADER(target) == hit->next_free) {
        /* merge */
        target->size += (hit->next_free->size + HEADER_SIZE);
        target->next_free = hit->next_free->next_free;
    }
    else {
        /* join next free block */
        target->next_free = hit->next_free;
    }
    if (NEXT_HEADER(hit) == target) {
        /* merge */
        hit->size += (target->size + HEADER_SIZE);
        hit->next_free = target->next_free;
    }
    else {
        /* join before free block */
        hit->next_free = target;
    }
    free_list = hit;
    target->flags = 0;
}




/* ========================================================================== */
/*  mini_gc                                                                   */
/* ========================================================================== */

struct root_range {
    void * start;
    void * end;
};

#define IS_MARKED(x) (FL_TEST(x, FL_ALLOC) && FL_TEST(x, FL_MARK))
#define ROOT_RANGES_LIMIT 1000

static struct root_range root_ranges[ROOT_RANGES_LIMIT];
static size_t root_ranges_used = 0;
static void * stack_start = NULL;
static void * stack_end = NULL;
static GC_Heap *hit_cache = NULL;

static GC_Heap *
is_pointer_to_heap(void *ptr)
{
    size_t i;

    if (hit_cache &&
        ((void *)hit_cache->slot) <= ptr &&
        (size_t)ptr < (((size_t)hit_cache->slot) + hit_cache->size))
        return hit_cache;

    for (i = 0; i < gc_heaps_used;  i++) {
        if ((((void *)gc_heaps[i].slot) <= ptr) &&
            ((size_t)ptr < (((size_t)gc_heaps[i].slot) + gc_heaps[i].size))) {
            hit_cache = &gc_heaps[i];
            return &gc_heaps[i];
        }
    }
    return NULL;
}

static Header *
get_header(GC_Heap *gh, void *ptr)
{
    Header *p, *pend, *pnext;

    pend = (Header *)(((size_t)gh->slot) + gh->size);
    for (p = gh->slot; p < pend; p = pnext) {
        pnext = NEXT_HEADER(p);
        if ((void *)(p+1) <= ptr && ptr < (void *)pnext) {
            return p;
        }
    }
    return NULL;
}

void
gc_init(void)
{
    long dummy;

    /* referenced bdw-gc mark_rts.c */
    dummy = 42;

    /* check stack grow */
    stack_start = ((void *)&dummy);
}

static void
set_stack_end(void)
{
    void *tmp;
    long dummy;

    /* referenced bdw-gc mark_rts.c */
    dummy = 42;

    stack_end = (void *)&dummy;
}

static void gc_mark_range(void *start, void *end);

static void
gc_mark(void * ptr)
{
    GC_Heap *gh;
    Header *hdr;

    /* mark check */
    if (!(gh = is_pointer_to_heap(ptr))) return;
    if (!(hdr = get_header(gh, ptr))) return;
    if (!FL_TEST(hdr, FL_ALLOC)) return;
    if (FL_TEST(hdr, FL_MARK)) return;

    /* marking */
    FL_SET(hdr, FL_MARK);
    DEBUG(printf("mark ptr : %p, header : %p\n", ptr, hdr));

    /* mark children */
    gc_mark_range((void *)(hdr+1), (void *)NEXT_HEADER(hdr));
}

static void
gc_mark_range(void *start, void *end)
{
    void *p;

    for (p = start; p < end; p++) {
        gc_mark(*(void **)p);
    }
}

static void
gc_mark_register(void)
{
    jmp_buf env;
    size_t i;
    
    setjmp(env);
    for (i = 0; i < sizeof(env); i++) {
        gc_mark(((void **)env)[i]);
    }
}

static void
gc_mark_stack(void)
{
    set_stack_end();
    if (stack_start > stack_end) {
        gc_mark_range(stack_end, stack_start);
    }
    else {
        gc_mark_range(stack_start, stack_end);
    }
}

static void
gc_sweep(void)
{
    size_t i;
    Header *p, *pend, *pnext;

    for (i = 0; i < gc_heaps_used; i++) {
        pend = (Header *)(((size_t)gc_heaps[i].slot) + gc_heaps[i].size);
        for (p = gc_heaps[i].slot; p < pend; p = NEXT_HEADER(p)) {
            if (FL_TEST(p, FL_ALLOC)) {
                if (FL_TEST(p, FL_MARK)) {
                    DEBUG(printf("mark unset : %p\n", p));
                    FL_UNSET(p, FL_MARK);
                }
                else {
                    mini_gc_free(p+1);
                }
            }
        }
    }
}

void
add_roots(void * start, void * end)
{
    void *tmp;
    if (start > end) {
        tmp = start;
        start = end;
        end = tmp;
    }
    root_ranges[root_ranges_used].start = start;
    root_ranges[root_ranges_used].end = end;
    root_ranges_used++;

    if (root_ranges_used >= ROOT_RANGES_LIMIT) {
        fputs("Root OverFlow", stderr);
        abort();
    }
}

void
garbage_collect(void)
{
    size_t i;

    /* marking machine context */
    gc_mark_register();
    gc_mark_stack();

    /* marking roots */
    for (i = 0; i < root_ranges_used; i++) {
        gc_mark_range(root_ranges[i].start, root_ranges[i].end);
    }

    /* sweeping */
    gc_sweep();
}


/* ========================================================================== */
/*  test                                                                      */
/* ========================================================================== */

static void
test_mini_gc_malloc_free(void)
{
    void *p1, *p2, *p3;

    /* malloc check */
    p1 = (void *)mini_gc_malloc(10);
    p2 = (void *)mini_gc_malloc(10);
    p3 = (void *)mini_gc_malloc(10);
    assert(((Header *)p1-1)->size == ALIGN(10, PTRSIZE));
    assert(((Header *)p1-1)->flags == FL_ALLOC);
    assert((Header *)(((size_t)(free_list+1)) + free_list->size) == ((Header *)p3-1));

    /* free check */
    mini_gc_free(p1);
    mini_gc_free(p3);
    mini_gc_free(p2);
    assert(free_list->next_free == free_list);
    assert((void *)gc_heaps[0].slot == (void *)free_list);
    assert(gc_heaps[0].size == TINY_HEAP_SIZE);
    assert(((Header *)p1-1)->flags == 0);

    /* grow check */
    p1 = mini_gc_malloc(TINY_HEAP_SIZE+80);
    assert(gc_heaps_used == 2);
    assert(gc_heaps[1].size == (TINY_HEAP_SIZE+80));
    mini_gc_free(p1);
}

static void
test_garbage_collect(void) {
    void *p;
    p = mini_gc_malloc(100);
    assert(FL_TEST((((Header *)p)-1), FL_ALLOC));
    p = 0;
    garbage_collect();
}

static void
test_garbage_collect_load_test(void) {
    void *p;
    int i;
    for (i = 0; i < 2000; i++) {
        p = mini_gc_malloc(100);
    }
    assert((((Header *)p)-1)->flags);
    assert(stack_end != stack_start);
}

static void
test(void)
{
    gc_init();
    test_mini_gc_malloc_free();
    test_garbage_collect();
    test_garbage_collect_load_test();
}


int
main(int argc, char **argv)
{
    if (argc == 2 && strcmp(argv[1], "test") == 0)  test();
    return 0;
}


================================================
FILE: gc.h
================================================
#ifndef _MINI_GC
#define _MINI_GC

void mini_gc_free(void *ptr);
void * mini_gc_malloc(size_t req_size);

void garbage_collect(void);
void gc_init(void);
void add_roots(void * start, void * end);

#endif