lama_byterun/runtime/gc.h

#ifndef __LAMA_GC__
#define __LAMA_GC__

#include "runtime_common.h"

#define GET_MARK_BIT(x) (((int)(x)) & 1)
#define SET_MARK_BIT(x) (x = (((int)(x)) | 1))
#define IS_ENQUEUED(x) (((int)(x)) & 2)
#define MAKE_ENQUEUED(x) (x = (((int)(x)) | 2))
#define MAKE_DEQUEUED(x) (x = (((int)(x)) & (~2)))
#define RESET_MARK_BIT(x) (x = (((int)(x)) & (~1)))
#define GET_FORWARD_ADDRESS(x)                                                                     \
  (((size_t)(x))                                                                                   \
   & (~3))   // since last 2 bits are used for mark-bit and enqueued-bit and due to correct alignment we can expect that last 2 bits don't influence address (they should always be zero)
#define SET_FORWARD_ADDRESS(x, addr)                                                               \
  (x = ((x & 3) | ((int)(addr))))   // take the last two bits as they are and make all others zero
#define EXTRA_ROOM_HEAP_COEFFICIENT 2   // TODO: tune this parameter
#ifdef DEBUG_VERSION
#  define MINIMUM_HEAP_CAPACITY (8)
#else
#  define MINIMUM_HEAP_CAPACITY (1 << 5)
#endif

#include <stdbool.h>
#include <stddef.h>

typedef enum { ARRAY, CLOSURE, STRING, SEXP } lama_type;

typedef struct {
  size_t *current;
} heap_iterator;

typedef struct {
  // holds type of object, which fields we are iterating over
  lama_type type;
  // here a pointer to the object header is stored
  void *obj_ptr;
  void *cur_field;
} obj_field_iterator;

typedef struct {
  size_t *begin;
  size_t *end;
  size_t *current;
  size_t  size;
} memory_chunk;

/* GC extra roots */
#define MAX_EXTRA_ROOTS_NUMBER 32

typedef struct {
  int    current_free;
  void **roots[MAX_EXTRA_ROOTS_NUMBER];
} extra_roots_pool;

// the only GC-related function that should be exposed, others are useful for tests and internal implementation
// allocates object of the given size on the heap
void *alloc(size_t);
// takes number of words as a parameter
void *gc_alloc(size_t);
// takes number of words as a parameter
void *gc_alloc_on_existing_heap(size_t);

// specific for mark-and-compact_phase gc
void mark (void *obj);
void mark_phase (void);
// written in ASM, scans stack for pointers to the heap and starts marking process
extern void
    __gc_root_scan_stack (void);   // TODO: write without ASM, since it is absolutely not necessary
// marks each pointer from extra roots
void scan_extra_roots (void);
#ifndef DEBUG_VERSION
// marks each valid pointer from global area
void scan_global_area (void);
#endif
// takes number of words that are required to be allocated somewhere on the heap
void compact_phase (size_t additional_size);
// specific for Lisp-2 algorithm
size_t compute_locations ();
void   update_references (memory_chunk *);
void   physically_relocate (memory_chunk *);

// written in ASM
extern void __gc_init (
    void);   // MANDATORY TO CALL BEFORE ANY INTERACTION WITH GC (apart from cases where we are working with virtual stack as happens in tests)
extern void __init (
    void);   // should be called before interaction with GC in case of using in tests with virtual stack, otherwise it is automatically invoked by __gc_init
extern void __shutdown (
    void);   // mostly useful for tests but basically you want to call this in case you want to deallocate all object allocated via GC
// written in ASM
extern void __pre_gc (void);
// written in ASM
extern void __post_gc (void);

// invoked from ASM
extern void gc_test_and_mark_root (size_t **root);
inline bool is_valid_heap_pointer (const size_t *);
inline bool is_valid_pointer (const size_t *);

void clear_extra_roots (void);

void push_extra_root (void **p);

void pop_extra_root (void **p);

/* Functions for tests */

#ifdef DEBUG_VERSION

// makes a snapshot of current objects in heap (both alive and dead), writes these ids to object_ids_buf,
// returns number of ids dumped
// object_ids_buf is pointer to area preallocated by user for dumping ids of objects in heap
// object_ids_buf_size is in WORDS, NOT BYTES
size_t objects_snapshot (int *object_ids_buf, size_t object_ids_buf_size);

// essential function to mock program stack
void set_stack (size_t stack_top, size_t stack_bottom);

// function to mock extra roots (Lama specific)
void set_extra_roots (size_t extra_roots_size, void **extra_roots_ptr);

#endif

/* Utility functions */

// accepts pointer to the start of the region and to the end of the region
// scans it and if it meets a pointer, it should be modified in according to forward address
void scan_and_fix_region (memory_chunk *old_heap, void *start, void *end);

// takes a pointer to an object content as an argument, returns forwarding address
size_t get_forward_address (void *obj);

// takes a pointer to an object content as an argument, sets forwarding address to value 'addr'
void set_forward_address (void *obj, size_t addr);

// takes a pointer to an object content as an argument, returns whether this object was marked as live
bool is_marked (void *obj);

// takes a pointer to an object content as an argument, marks the object as live
void mark_object (void *obj);

// takes a pointer to an object content as an argument, marks the object as dead
void unmark_object (void *obj);

// takes a pointer to an object content as an argument, returns whether this object was enqueued to the queue (which is used in mark phase)
bool is_enqueued (void *obj);

// takes a pointer to an object content as an argument, marks object as enqueued
void make_enqueued (void *obj);

// takes a pointer to an object content as an argument, unmarks object as enqueued
void make_dequeued (void *obj);

// returns iterator to an object with the lowest address
heap_iterator heap_begin_iterator ();
void          heap_next_obj_iterator (heap_iterator *it);
bool          heap_is_done_iterator (heap_iterator *it);

// returns correct type when pointer to actual data is passed (header is excluded)
lama_type get_type_row_ptr (void *ptr);
// returns correct type when pointer to an object header is passed
lama_type get_type_header_ptr (void *ptr);

// returns correct object size (together with header) of an object, ptr is pointer to an actual data is passed (header is excluded)
size_t obj_size_row_ptr (void *ptr);
// returns correct object size (together with header) of an object, ptr is pointer to an object header
size_t obj_size_header_ptr (void *ptr);

// returns total padding size that we need to store given object type
size_t get_header_size (lama_type type);
// returns number of bytes that are required to allocate array with 'sz' elements (header included)
size_t array_size (size_t sz);
// returns number of bytes that are required to allocate string of length 'l' (header included)
size_t string_size (size_t len);
// TODO: ask if it is actually so? number of captured elements is actually sz-1 and 1 extra word is code ptr?
// returns number of bytes that are required to allocate closure with 'sz-1' captured values (header included)
size_t closure_size (size_t sz);
// returns number of bytes that are required to allocate s-expression with 'members' fields (header included)
size_t sexp_size (size_t members);

// returns an iterator over object fields, obj is ptr to object header
// (in case of s-exp, it is mandatory that obj ptr is very beginning of the object,
// considering that now we store two versions of header in there)
obj_field_iterator field_begin_iterator (void *obj);
// returns an iterator over object fields which are actual pointers, obj is ptr to object header
// (in case of s-exp, it is mandatory that obj ptr is very beginning of the object,
// considering that now we store two versions of header in there)
obj_field_iterator ptr_field_begin_iterator (void *obj);
// moves the iterator to next object field
void obj_next_field_iterator (obj_field_iterator *it);
// moves the iterator to the next object field which is an actual pointer
void obj_next_ptr_field_iterator (obj_field_iterator *it);
// returns if we are done iterating over fields of the object
bool field_is_done_iterator (obj_field_iterator *it);
// ptr is pointer to the actual object content, returns pointer to the very beginning of the object (header)
void *get_obj_header_ptr (void *ptr);
void *get_object_content_ptr (void *header_ptr);
void *get_end_of_obj (void *header_ptr);

void *alloc_string (int len);
void *alloc_array (int len);
void *alloc_sexp (int members);
void *alloc_closure (int captured);

#endif