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1.1 noro 1: This is an ASCII diagram of the data structure used to check pointer
2: validity. It was provided by Dave Barrett <barrett@asgard.cs.colorado.edu>,
3: and should be of use to others attempting to understand the code.
4: The data structure in GC4.X is essentially the same. -HB
5:
6:
7:
8:
9: Data Structure used by GC_base in gc3.7:
10: 21-Apr-94
11:
12:
13:
14:
15: 63 LOG_TOP_SZ[11] LOG_BOTTOM_SZ[10] LOG_HBLKSIZE[13]
16: +------------------+----------------+------------------+------------------+
17: p:| | TL_HASH(hi) | | HBLKDISPL(p) |
18: +------------------+----------------+------------------+------------------+
19: \-----------------------HBLKPTR(p)-------------------/
20: \------------hi-------------------/
21: \______ ________/ \________ _______/ \________ _______/
22: V V V
23: | | |
24: GC_top_index[] | | |
25: --- +--------------+ | | |
26: ^ | | | | |
27: | | | | | |
28: TOP +--------------+<--+ | |
29: _SZ +-<| [] | * | |
30: (items)| +--------------+ if 0 < bi< HBLKSIZE | |
31: | | | | then large object | |
32: | | | | starts at the bi'th | |
33: v | | | HBLK before p. | i |
34: --- | +--------------+ | (word- |
35: v | aligned) |
36: bi= |GET_BI(p){->hash_link}->key==hi | |
37: v | |
38: | (bottom_index) \ scratch_alloc'd | |
39: | ( struct bi ) / by get_index() | |
40: --- +->+--------------+ | |
41: ^ | | | |
42: ^ | | | |
43: BOTTOM | | ha=GET_HDR_ADDR(p) | |
44: _SZ(items)+--------------+<----------------------+ +-------+
45: | +--<| index[] | |
46: | | +--------------+ GC_obj_map: v
47: | | | | from / +-+-+-----+-+-+-+-+ ---
48: v | | | GC_add < 0| | | | | | | | ^
49: --- | +--------------+ _map_entry \ +-+-+-----+-+-+-+-+ |
50: | | asc_link | +-+-+-----+-+-+-+-+ MAXOBJSZ
51: | +--------------+ +-->| | | j | | | | | +1
52: | | key | | +-+-+-----+-+-+-+-+ |
53: | +--------------+ | +-+-+-----+-+-+-+-+ |
54: | | hash_link | | | | | | | | | | v
55: | +--------------+ | +-+-+-----+-+-+-+-+ ---
56: | | |<--MAX_OFFSET--->|
57: | | (bytes)
58: HDR(p)| GC_find_header(p) | |<--MAP_ENTRIES-->|
59: | \ from | =HBLKSIZE/WORDSZ
60: | (hdr) (struct hblkhdr) / alloc_hdr() | (1024 on Alpha)
61: +-->+----------------------+ | (8/16 bits each)
62: GET_HDR(p)| word hb_sz (words) | |
63: +----------------------+ |
64: | struct hblk *hb_next | |
65: +----------------------+ |
66: |mark_proc hb_mark_proc| |
67: +----------------------+ |
68: | char * hb_map |>-------------+
69: +----------------------+
70: | ushort hb_obj_kind |
71: +----------------------+
72: | hb_last_reclaimed |
73: --- +----------------------+
74: ^ | |
75: MARK_BITS| hb_marks[] | *if hdr is free, hb_sz + DISCARD_WORDS
76: _SZ(words)| | is the size of a heap chunk (struct hblk)
77: v | | of at least MININCR*HBLKSIZE bytes (below),
78: --- +----------------------+ otherwise, size of each object in chunk.
79:
80: Dynamic data structures above are interleaved throughout the heap in blocks of
81: size MININCR * HBLKSIZE bytes as done by gc_scratch_alloc which cannot be
82: freed; free lists are used (e.g. alloc_hdr). HBLKs's below are collected.
83:
84: (struct hblk)
85: --- +----------------------+ < HBLKSIZE --- --- DISCARD_
86: ^ |garbage[DISCARD_WORDS]| aligned ^ ^ HDR_BYTES WORDS
87: | | | | v (bytes) (words)
88: | +-----hb_body----------+ < WORDSZ | --- ---
89: | | | aligned | ^ ^
90: | | Object 0 | | hb_sz |
91: | | | i |(word- (words)|
92: | | | (bytes)|aligned) v |
93: | + - - - - - - - - - - -+ --- | --- |
94: | | | ^ | ^ |
95: n * | | j (words) | hb_sz BODY_SZ
96: HBLKSIZE | Object 1 | v v | (words)
97: (bytes) | |--------------- v MAX_OFFSET
98: | + - - - - - - - - - - -+ --- (bytes)
99: | | | !All_INTERIOR_PTRS ^ |
100: | | | sets j only for hb_sz |
101: | | Object N | valid object offsets. | |
102: v | | All objects WORDSZ v v
103: --- +----------------------+ aligned. --- ---
104:
105: DISCARD_WORDS is normally zero. Indeed the collector has not been tested
106: with another value in ages.