+++ /dev/null
-This is an ASCII diagram of the data structure used to check pointer
-validity. It was provided by Dave Barrett,
-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.
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