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
|
/*
* Copyright (C) 2017-2023 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "MarkingConstraintSet.h"
#include "MarkingConstraintSolver.h"
#include "Options.h"
#include "SimpleMarkingConstraint.h"
#include "SuperSampler.h"
#include <wtf/Function.h>
#include <wtf/TZoneMallocInlines.h>
namespace JSC {
WTF_MAKE_TZONE_ALLOCATED_IMPL(MarkingConstraintSet);
MarkingConstraintSet::MarkingConstraintSet(JSC::Heap& heap)
: m_heap(heap)
{
}
MarkingConstraintSet::~MarkingConstraintSet() = default;
void MarkingConstraintSet::didStartMarking()
{
m_unexecutedRoots.clearAll();
m_unexecutedOutgrowths.clearAll();
for (auto& constraint : m_set) {
constraint->resetStats();
switch (constraint->volatility()) {
case ConstraintVolatility::GreyedByExecution:
m_unexecutedRoots.set(constraint->index());
break;
case ConstraintVolatility::GreyedByMarking:
m_unexecutedOutgrowths.set(constraint->index());
break;
case ConstraintVolatility::SeldomGreyed:
break;
}
}
m_iteration = 1;
}
void MarkingConstraintSet::add(CString abbreviatedName, CString name, MarkingConstraintExecutorPair&& executors, ConstraintVolatility volatility, ConstraintConcurrency concurrency, ConstraintParallelism parallelism)
{
add(makeUnique<SimpleMarkingConstraint>(WTFMove(abbreviatedName), WTFMove(name), WTFMove(executors), volatility, concurrency, parallelism));
}
void MarkingConstraintSet::add(
std::unique_ptr<MarkingConstraint> constraint)
{
constraint->m_index = m_set.size();
m_ordered.append(constraint.get());
if (constraint->volatility() == ConstraintVolatility::GreyedByMarking)
m_outgrowths.append(constraint.get());
m_set.append(WTFMove(constraint));
}
bool MarkingConstraintSet::executeConvergence(SlotVisitor& visitor)
{
bool result = executeConvergenceImpl(visitor);
dataLogIf(Options::logGC(), " ");
return result;
}
bool MarkingConstraintSet::isWavefrontAdvancing(SlotVisitor& visitor)
{
for (MarkingConstraint* outgrowth : m_outgrowths) {
if (outgrowth->workEstimate(visitor))
return true;
}
return false;
}
bool MarkingConstraintSet::executeConvergenceImpl(SlotVisitor& visitor)
{
SuperSamplerScope superSamplerScope(false);
MarkingConstraintSolver solver(*this);
unsigned iteration = m_iteration++;
dataLogIf(Options::logGC(), "i#", iteration, ":");
if (iteration == 1) {
// First iteration is before any visitor draining, so it's unlikely to trigger any constraints
// other than roots.
solver.drain(m_unexecutedRoots);
return false;
}
if (iteration == 2) {
solver.drain(m_unexecutedOutgrowths);
return false;
}
// We want to keep preferring the outgrowth constraints - the ones that need to be fixpointed
// even in a stop-the-world GC - until they stop producing. They have a tendency to go totally
// silent at some point during GC, at which point it makes sense not to run them again until
// the end. Outgrowths producing new information corresponds almost exactly to the wavefront
// advancing: it usually means that we are marking objects that should be marked based on
// other objects that we would have marked anyway. Once the wavefront is no longer advancing,
// we want to run mostly the root constraints (based on their predictions of how much work
// they will have) because at this point we are just trying to outpace the retreating
// wavefront.
//
// Note that this function (executeConvergenceImpl) only returns true if it runs all
// constraints. So, all we are controlling are the heuristics that say which constraints to
// run first. Choosing the constraints that are the most likely to produce means running fewer
// constraints before returning.
bool isWavefrontAdvancing = this->isWavefrontAdvancing(visitor);
std::sort(
m_ordered.begin(), m_ordered.end(),
[&] (MarkingConstraint* a, MarkingConstraint* b) -> bool {
// Remember: return true if a should come before b.
auto volatilityScore = [] (MarkingConstraint* constraint) -> unsigned {
return constraint->volatility() == ConstraintVolatility::GreyedByMarking ? 1 : 0;
};
unsigned aVolatilityScore = volatilityScore(a);
unsigned bVolatilityScore = volatilityScore(b);
if (aVolatilityScore != bVolatilityScore) {
if (isWavefrontAdvancing)
return aVolatilityScore > bVolatilityScore;
else
return aVolatilityScore < bVolatilityScore;
}
double aWorkEstimate = a->workEstimate(visitor);
double bWorkEstimate = b->workEstimate(visitor);
if (aWorkEstimate != bWorkEstimate)
return aWorkEstimate > bWorkEstimate;
// This causes us to use SeldomGreyed vs GreyedByExecution as a final tie-breaker.
return a->volatility() > b->volatility();
});
solver.converge(m_ordered);
// Return true if we've converged. That happens if we did not visit anything.
return !solver.didVisitSomething();
}
void MarkingConstraintSet::executeAllSynchronously(AbstractSlotVisitor& visitor)
{
for (auto& constraint : m_set)
constraint->executeSynchronously(visitor);
dataLogIf(Options::logGC(), " ");
}
} // namespace JSC
|
