summaryrefslogtreecommitdiff
path: root/js/src/gc/NurseryAwareHashMap.h
blob: 9f9486deaa7cc40fed19ee6cc99d6b8dba9803a0 (plain)
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
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef gc_NurseryAwareHashMap_h
#define gc_NurseryAwareHashMap_h

namespace js {

namespace detail {
// This class only handles the incremental case and does not deal with nursery
// pointers. The only users should be for NurseryAwareHashMap; it is defined
// externally because we need a GCPolicy for its use in the contained map.
template <typename T>
class UnsafeBareReadBarriered : public ReadBarrieredBase<T>
{
  public:
    UnsafeBareReadBarriered() : ReadBarrieredBase<T>(JS::GCPolicy<T>::initial()) {}
    MOZ_IMPLICIT UnsafeBareReadBarriered(const T& v) : ReadBarrieredBase<T>(v) {}
    explicit UnsafeBareReadBarriered(const UnsafeBareReadBarriered& v) : ReadBarrieredBase<T>(v) {}
    UnsafeBareReadBarriered(UnsafeBareReadBarriered&& v)
      : ReadBarrieredBase<T>(mozilla::Move(v))
    {}

    UnsafeBareReadBarriered& operator=(const UnsafeBareReadBarriered& v) {
        this->value = v.value;
        return *this;
    }

    UnsafeBareReadBarriered& operator=(const T& v) {
        this->value = v;
        return *this;
    }

    const T get() const {
        if (!InternalBarrierMethods<T>::isMarkable(this->value))
            return JS::GCPolicy<T>::initial();
        this->read();
        return this->value;
    }

    explicit operator bool() const {
        return bool(this->value);
    }

    const T unbarrieredGet() const { return this->value; }
    T* unsafeGet() { return &this->value; }
    T const* unsafeGet() const { return &this->value; }
};
} // namespace detail

// The "nursery aware" hash map is a special case of GCHashMap that is able to
// treat nursery allocated members weakly during a minor GC: e.g. it allows for
// nursery allocated objects to be collected during nursery GC where a normal
// hash table treats such edges strongly.
//
// Doing this requires some strong constraints on what can be stored in this
// table and how it can be accessed. At the moment, this table assumes that
// all values contain a strong reference to the key. It also requires the
// policy to contain an |isTenured| and |needsSweep| members, which is fairly
// non-standard. This limits its usefulness to the CrossCompartmentMap at the
// moment, but might serve as a useful base for other tables in future.
template <typename Key,
          typename Value,
          typename HashPolicy = DefaultHasher<Key>,
          typename AllocPolicy = TempAllocPolicy>
class NurseryAwareHashMap
{
    using BarrieredValue = detail::UnsafeBareReadBarriered<Value>;
    using MapType = GCRekeyableHashMap<Key, BarrieredValue, HashPolicy, AllocPolicy>;
    MapType map;

    // Keep a list of all keys for which JS::GCPolicy<Key>::isTenured is false.
    // This lets us avoid a full traveral of the map on each minor GC, keeping
    // the minor GC times proportional to the nursery heap size.
    Vector<Key, 0, AllocPolicy> nurseryEntries;

  public:
    using Lookup = typename MapType::Lookup;
    using Ptr = typename MapType::Ptr;
    using Range = typename MapType::Range;

    explicit NurseryAwareHashMap(AllocPolicy a = AllocPolicy()) : map(a) {}

    MOZ_MUST_USE bool init(uint32_t len = 16) { return map.init(len); }

    bool empty() const { return map.empty(); }
    Ptr lookup(const Lookup& l) const { return map.lookup(l); }
    void remove(Ptr p) { map.remove(p); }
    Range all() const { return map.all(); }
    struct Enum : public MapType::Enum {
        explicit Enum(NurseryAwareHashMap& namap) : MapType::Enum(namap.map) {}
    };
    size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
        return map.sizeOfExcludingThis(mallocSizeOf);
    }
    size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
        return map.sizeOfIncludingThis(mallocSizeOf);
    }

    MOZ_MUST_USE bool put(const Key& k, const Value& v) {
        auto p = map.lookupForAdd(k);
        if (p) {
            if (!JS::GCPolicy<Key>::isTenured(k) || !JS::GCPolicy<Value>::isTenured(v)) {
                if (!nurseryEntries.append(k))
                    return false;
            }
            p->value() = v;
            return true;
        }

        bool ok = map.add(p, k, v);
        if (!ok)
            return false;

        if (!JS::GCPolicy<Key>::isTenured(k) || !JS::GCPolicy<Value>::isTenured(v)) {
            if (!nurseryEntries.append(k)) {
                map.remove(k);
                return false;
            }
        }

        return true;
    }

    void sweepAfterMinorGC(JSTracer* trc) {
        for (auto& key : nurseryEntries) {
            auto p = map.lookup(key);
            if (!p)
                continue;

            // Drop the entry if the value is not marked.
            if (JS::GCPolicy<BarrieredValue>::needsSweep(&p->value())) {
                map.remove(key);
                continue;
            }

            // Update and relocate the key, if the value is still needed.
            //
            // Note that this currently assumes that all Value will contain a
            // strong reference to Key, as per its use as the
            // CrossCompartmentWrapperMap. We may need to make the following
            // behavior more dynamic if we use this map in other nursery-aware
            // contexts.
            Key copy(key);
            mozilla::DebugOnly<bool> sweepKey = JS::GCPolicy<Key>::needsSweep(&copy);
            MOZ_ASSERT(!sweepKey);
            map.rekeyIfMoved(key, copy);
        }
        nurseryEntries.clear();
    }

    void sweep() {
        MOZ_ASSERT(nurseryEntries.empty());
        map.sweep();
    }
};

} // namespace js

namespace JS {
template <typename T>
struct GCPolicy<js::detail::UnsafeBareReadBarriered<T>>
{
    static void trace(JSTracer* trc, js::detail::UnsafeBareReadBarriered<T>* thingp,
                      const char* name)
    {
        js::TraceEdge(trc, thingp, name);
    }
    static bool needsSweep(js::detail::UnsafeBareReadBarriered<T>* thingp) {
        return js::gc::IsAboutToBeFinalized(thingp);
    }
};
} // namespace JS

#endif // gc_NurseryAwareHashMap_h