| This is an ASCII diagram of the data structure used to check pointer |
| validity. It was provided by Dave Barrett <barrett@asgard.cs.colorado.edu>, |
| and should be of use to others attempting to understand the code. |
| The data structure in GC4.X is essentially the same. -HB |
| |
| |
| |
| |
| Data Structure used by GC_base in gc3.7: |
| 21-Apr-94 |
| |
| |
| |
| |
| 63 LOG_TOP_SZ[11] LOG_BOTTOM_SZ[10] LOG_HBLKSIZE[13] |
| +------------------+----------------+------------------+------------------+ |
| p:| | TL_HASH(hi) | | HBLKDISPL(p) | |
| +------------------+----------------+------------------+------------------+ |
| \-----------------------HBLKPTR(p)-------------------/ |
| \------------hi-------------------/ |
| \______ ________/ \________ _______/ \________ _______/ |
| V V V |
| | | | |
| GC_top_index[] | | | |
| --- +--------------+ | | | |
| ^ | | | | | |
| | | | | | | |
| TOP +--------------+<--+ | | |
| _SZ +-<| [] | * | | |
| (items)| +--------------+ if 0 < bi< HBLKSIZE | | |
| | | | | then large object | | |
| | | | | starts at the bi'th | | |
| v | | | HBLK before p. | i | |
| --- | +--------------+ | (word- | |
| v | aligned) | |
| bi= |GET_BI(p){->hash_link}->key==hi | | |
| v | | |
| | (bottom_index) \ scratch_alloc'd | | |
| | ( struct bi ) / by get_index() | | |
| --- +->+--------------+ | | |
| ^ | | | | |
| ^ | | | | |
| BOTTOM | | ha=GET_HDR_ADDR(p) | | |
| _SZ(items)+--------------+<----------------------+ +-------+ |
| | +--<| index[] | | |
| | | +--------------+ GC_obj_map: v |
| | | | | from / +-+-+-----+-+-+-+-+ --- |
| v | | | GC_add < 0| | | | | | | | ^ |
| --- | +--------------+ _map_entry \ +-+-+-----+-+-+-+-+ | |
| | | asc_link | +-+-+-----+-+-+-+-+ MAXOBJSZ |
| | +--------------+ +-->| | | j | | | | | +1 |
| | | key | | +-+-+-----+-+-+-+-+ | |
| | +--------------+ | +-+-+-----+-+-+-+-+ | |
| | | hash_link | | | | | | | | | | v |
| | +--------------+ | +-+-+-----+-+-+-+-+ --- |
| | | |<--MAX_OFFSET--->| |
| | | (bytes) |
| HDR(p)| GC_find_header(p) | |<--MAP_ENTRIES-->| |
| | \ from | =HBLKSIZE/WORDSZ |
| | (hdr) (struct hblkhdr) / alloc_hdr() | (1024 on Alpha) |
| +-->+----------------------+ | (8/16 bits each) |
| GET_HDR(p)| word hb_sz (words) | | |
| +----------------------+ | |
| | struct hblk *hb_next | | |
| +----------------------+ | |
| |mark_proc hb_mark_proc| | |
| +----------------------+ | |
| | char * hb_map |>-------------+ |
| +----------------------+ |
| | ushort hb_obj_kind | |
| +----------------------+ |
| | hb_last_reclaimed | |
| --- +----------------------+ |
| ^ | | |
| MARK_BITS| hb_marks[] | *if hdr is free, hb_sz + DISCARD_WORDS |
| _SZ(words)| | is the size of a heap chunk (struct hblk) |
| v | | of at least MININCR*HBLKSIZE bytes (below), |
| --- +----------------------+ otherwise, size of each object in chunk. |
| |
| Dynamic data structures above are interleaved throughout the heap in blocks of |
| size MININCR * HBLKSIZE bytes as done by gc_scratch_alloc which cannot be |
| freed; free lists are used (e.g. alloc_hdr). HBLKs's below are collected. |
| |
| (struct hblk) |
| --- +----------------------+ < HBLKSIZE --- --- DISCARD_ |
| ^ |garbage[DISCARD_WORDS]| aligned ^ ^ HDR_BYTES WORDS |
| | | | | v (bytes) (words) |
| | +-----hb_body----------+ < WORDSZ | --- --- |
| | | | aligned | ^ ^ |
| | | Object 0 | | hb_sz | |
| | | | i |(word- (words)| |
| | | | (bytes)|aligned) v | |
| | + - - - - - - - - - - -+ --- | --- | |
| | | | ^ | ^ | |
| n * | | j (words) | hb_sz BODY_SZ |
| HBLKSIZE | Object 1 | v v | (words) |
| (bytes) | |--------------- v MAX_OFFSET |
| | + - - - - - - - - - - -+ --- (bytes) |
| | | | !All_INTERIOR_PTRS ^ | |
| | | | sets j only for hb_sz | |
| | | Object N | valid object offsets. | | |
| v | | All objects WORDSZ v v |
| --- +----------------------+ aligned. --- --- |
| |
| DISCARD_WORDS is normally zero. Indeed the collector has not been tested |
| with another value in ages. |
