1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
|
#
#
# Nim's Runtime Library
# (c) Copyright 2019 Andreas Rumpf
#
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
#
# Cycle collector based on Lins' Jump Stack and other ideas,
# see for example:
# https://pdfs.semanticscholar.org/f2b2/0d168acf38ff86305809a55ef2c5d6ebc787.pdf
# Further refinement in 2008 by the notion of "critical links", see
# "Cyclic reference counting" by Rafael Dueire Lins
# R.D. Lins / Information Processing Letters 109 (2008) 71–78
const
colGreen = 0b000
colYellow = 0b001
colRed = 0b010
jumpStackFlag = 0b100 # stored in jumpstack
rcShift = 3 # shift by rcShift to get the reference counter
colorMask = 0b011
type
TraceProc = proc (p, env: pointer) {.nimcall, benign.}
DisposeProc = proc (p: pointer) {.nimcall, benign.}
template color(c): untyped = c.rc and colorMask
template setColor(c, col) =
when col == colGreen:
c.rc = c.rc and not colorMask
else:
c.rc = c.rc and not colorMask or col
proc nimIncRefCyclic(p: pointer) {.compilerRtl, inl.} =
let h = head(p)
inc h.rc, rcIncrement
h.setColor colYellow # mark as potential cycle!
proc markCyclic*[T](x: ref T) {.inline.} =
## Mark the underlying object as a candidate for cycle collections.
## Experimental API. Do not use!
let h = head(cast[pointer](x))
h.setColor colYellow
type
CellTuple = (Cell, PNimType)
CellArray = ptr UncheckedArray[CellTuple]
CellSeq = object
len, cap: int
d: CellArray
GcEnv = object
traceStack: CellSeq
jumpStack: CellSeq
# ------------------- cell seq handling --------------------------------------
proc add(s: var CellSeq, c: Cell; t: PNimType) {.inline.} =
if s.len >= s.cap:
s.cap = s.cap * 3 div 2
when defined(useMalloc):
var d = cast[CellArray](c_malloc(uint(s.cap * sizeof(CellTuple))))
else:
var d = cast[CellArray](alloc(s.cap * sizeof(CellTuple)))
copyMem(d, s.d, s.len * sizeof(CellTuple))
when defined(useMalloc):
c_free(s.d)
else:
dealloc(s.d)
s.d = d
# XXX: realloc?
s.d[s.len] = (c, t)
inc(s.len)
proc init(s: var CellSeq, cap: int = 1024) =
s.len = 0
s.cap = cap
when defined(useMalloc):
s.d = cast[CellArray](c_malloc(uint(s.cap * sizeof(CellTuple))))
else:
s.d = cast[CellArray](alloc(s.cap * sizeof(CellTuple)))
proc deinit(s: var CellSeq) =
when defined(useMalloc):
c_free(s.d)
else:
dealloc(s.d)
s.d = nil
s.len = 0
s.cap = 0
proc pop(s: var CellSeq): (Cell, PNimType) =
result = s.d[s.len-1]
dec s.len
# ----------------------------------------------------------------------------
proc trace(s: Cell; desc: PNimType; j: var GcEnv) {.inline.} =
if desc.traceImpl != nil:
var p = s +! sizeof(RefHeader)
cast[TraceProc](desc.traceImpl)(p, addr(j))
proc free(s: Cell; desc: PNimType) {.inline.} =
when traceCollector:
cprintf("[From ] %p rc %ld color %ld in jumpstack %ld\n", s, s.rc shr rcShift,
s.color, s.rc and jumpStackFlag)
var p = s +! sizeof(RefHeader)
if desc.disposeImpl != nil:
cast[DisposeProc](desc.disposeImpl)(p)
nimRawDispose(p)
proc collect(s: Cell; desc: PNimType; j: var GcEnv) =
if s.color == colRed:
s.setColor colGreen
trace(s, desc, j)
while j.traceStack.len > 0:
let (t, desc) = j.traceStack.pop()
if t.color == colRed:
t.setColor colGreen
trace(t, desc, j)
free(t, desc)
free(s, desc)
#cprintf("[Cycle free] %p %ld\n", s, s.rc shr rcShift)
proc markRed(s: Cell; desc: PNimType; j: var GcEnv) =
if s.color != colRed:
s.setColor colRed
trace(s, desc, j)
while j.traceStack.len > 0:
let (t, desc) = j.traceStack.pop()
when traceCollector:
cprintf("[Cycle dec] %p %ld color %ld in jumpstack %ld\n", t, t.rc shr rcShift, t.color, t.rc and jumpStackFlag)
dec t.rc, rcIncrement
if (t.rc and not rcMask) >= 0 and (t.rc and jumpStackFlag) == 0:
t.rc = t.rc or jumpStackFlag
when traceCollector:
cprintf("[Now in jumpstack] %p %ld color %ld in jumpstack %ld\n", t, t.rc shr rcShift, t.color, t.rc and jumpStackFlag)
j.jumpStack.add(t, desc)
if t.color != colRed:
t.setColor colRed
trace(t, desc, j)
proc scanGreen(s: Cell; desc: PNimType; j: var GcEnv) =
s.setColor colGreen
trace(s, desc, j)
while j.traceStack.len > 0:
let (t, desc) = j.traceStack.pop()
if t.color != colGreen:
t.setColor colGreen
trace(t, desc, j)
inc t.rc, rcIncrement
when traceCollector:
cprintf("[Cycle inc] %p %ld color %ld\n", t, t.rc shr rcShift, t.color)
proc nimTraceRef(p: pointer; desc: PNimType; env: pointer) {.compilerRtl.} =
if p != nil:
var t = head(p)
var j = cast[ptr GcEnv](env)
j.traceStack.add(t, desc)
proc nimTraceRefDyn(p: pointer; env: pointer) {.compilerRtl.} =
if p != nil:
let desc = cast[ptr PNimType](p)[]
var t = head(p)
var j = cast[ptr GcEnv](env)
j.traceStack.add(t, desc)
proc scan(s: Cell; desc: PNimType; j: var GcEnv) =
when traceCollector:
cprintf("[doScanGreen] %p %ld\n", s, s.rc shr rcShift)
# even after trial deletion, `s` is still alive, so undo
# the decrefs by calling `scanGreen`:
if (s.rc and not rcMask) >= 0:
scanGreen(s, desc, j)
s.setColor colYellow
else:
# first we have to repair all the nodes we have seen
# that are still alive; we also need to mark what they
# refer to as alive:
while j.jumpStack.len > 0:
let (t, desc) = j.jumpStack.pop
# not in jump stack anymore!
t.rc = t.rc and not jumpStackFlag
if t.color == colRed and (t.rc and not rcMask) >= 0:
scanGreen(t, desc, j)
t.setColor colYellow
when traceCollector:
cprintf("[jump stack] %p %ld\n", t, t.rc shr rcShift)
# we have proven that `s` and its subgraph are dead, so we can
# collect these nodes:
collect(s, desc, j)
proc traceCycle(s: Cell; desc: PNimType) {.noinline.} =
when traceCollector:
cprintf("[traceCycle] %p %ld\n", s, s.rc shr rcShift)
var j: GcEnv
init j.jumpStack
init j.traceStack
markRed(s, desc, j)
scan(s, desc, j)
while j.jumpStack.len > 0:
let (t, desc) = j.jumpStack.pop
# not in jump stack anymore!
t.rc = t.rc and not jumpStackFlag
deinit j.jumpStack
deinit j.traceStack
proc nimDecRefIsLastCyclicDyn(p: pointer): bool {.compilerRtl, inl.} =
if p != nil:
var cell = head(p)
if (cell.rc and not rcMask) == 0:
result = true
#cprintf("[DESTROY] %p\n", p)
else:
dec cell.rc, rcIncrement
if cell.color == colYellow:
let desc = cast[ptr PNimType](p)[]
traceCycle(cell, desc)
# According to Lins it's correct to do nothing else here.
#cprintf("[DeCREF] %p\n", p)
proc nimDecRefIsLastCyclicStatic(p: pointer; desc: PNimType): bool {.compilerRtl, inl.} =
if p != nil:
var cell = head(p)
if (cell.rc and not rcMask) == 0:
result = true
#cprintf("[DESTROY] %p %s\n", p, desc.name)
else:
dec cell.rc, rcIncrement
if cell.color == colYellow: traceCycle(cell, desc)
#cprintf("[DeCREF] %p %s %ld\n", p, desc.name, cell.rc)
|