1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/js/src/jsweakcache.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,107 @@
1.4 +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
1.5 + * vim: set ts=8 sts=4 et sw=4 tw=99:
1.6 + * This Source Code Form is subject to the terms of the Mozilla Public
1.7 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.8 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.9 +
1.10 +#ifndef jsweakcache_h
1.11 +#define jsweakcache_h
1.12 +
1.13 +#include "jscntxt.h"
1.14 +#include "gc/Marking.h"
1.15 +#include "js/HashTable.h"
1.16 +#include "vm/Runtime.h"
1.17 +
1.18 +namespace js {
1.19 +
1.20 +// A WeakCache is used to map a key to a value similar to an HashMap except
1.21 +// that its entries are garbage collected. An entry is kept as long as
1.22 +// both the key and value are marked.
1.23 +//
1.24 +// No mark function is provided with this weak container. However, this weak
1.25 +// container should take part in the sweep phase.
1.26 +template <class Key, class Value,
1.27 + class HashPolicy = DefaultHasher<Key>,
1.28 + class AllocPolicy = RuntimeAllocPolicy>
1.29 +class WeakCache : public HashMap<Key, Value, HashPolicy, AllocPolicy> {
1.30 + private:
1.31 + typedef HashMap<Key, Value, HashPolicy, AllocPolicy> Base;
1.32 + typedef typename Base::Range Range;
1.33 + typedef typename Base::Enum Enum;
1.34 +
1.35 + public:
1.36 + explicit WeakCache(JSRuntime *rt) : Base(rt) { }
1.37 + explicit WeakCache(JSContext *cx) : Base(cx->runtime()) { }
1.38 +
1.39 + public:
1.40 + // Sweep all entries which have unmarked key or value.
1.41 + void sweep(FreeOp *fop) {
1.42 + // Remove all entries whose keys/values remain unmarked.
1.43 + for (Enum e(*this); !e.empty(); e.popFront()) {
1.44 + // Checking IsMarked() may update the location of the Key (or Value).
1.45 + // Pass in a stack local, then manually update the backing heap store.
1.46 + Key k(e.front().key);
1.47 + bool isKeyDying = gc::IsAboutToBeFinalized(&k);
1.48 +
1.49 + if (isKeyDying || gc::IsAboutToBeFinalized(e.front().value)) {
1.50 + e.removeFront();
1.51 + } else {
1.52 + // Potentially update the location of the Key.
1.53 + // The Value had its heap addresses correctly passed to IsMarked(),
1.54 + // and therefore has already been updated if necessary.
1.55 + // e.rekeyFront(k);
1.56 + }
1.57 + }
1.58 +
1.59 +#if DEBUG
1.60 + // Once we've swept, all remaining edges should stay within the
1.61 + // known-live part of the graph.
1.62 + for (Range r = Base::all(); !r.empty(); r.popFront()) {
1.63 + Key k(r.front().key);
1.64 +
1.65 + JS_ASSERT(!gc::IsAboutToBeFinalized(&k));
1.66 + JS_ASSERT(!gc::IsAboutToBeFinalized(r.front().value));
1.67 +
1.68 + // Assert that IsMarked() did not perform relocation.
1.69 + JS_ASSERT(k == r.front().key);
1.70 + }
1.71 +#endif
1.72 + }
1.73 +};
1.74 +
1.75 +// A WeakValueCache is similar to a WeakCache, except keys are never marked.
1.76 +// This is useful for weak maps where the keys are primitive values such as uint32_t.
1.77 +template <class Key, class Value,
1.78 + class HashPolicy = DefaultHasher<Key>,
1.79 + class AllocPolicy = RuntimeAllocPolicy>
1.80 +class WeakValueCache : public HashMap<Key, Value, HashPolicy, AllocPolicy>
1.81 +{
1.82 + public:
1.83 + typedef HashMap<Key, Value, HashPolicy, AllocPolicy> Base;
1.84 + typedef typename Base::Range Range;
1.85 + typedef typename Base::Enum Enum;
1.86 +
1.87 + explicit WeakValueCache(JSRuntime *rt) : Base(rt) { }
1.88 + explicit WeakValueCache(JSContext *cx) : Base(cx->runtime()) { }
1.89 +
1.90 + public:
1.91 + // Sweep all entries which have unmarked key or value.
1.92 + void sweep(FreeOp *fop) {
1.93 + // Remove all entries whose values remain unmarked.
1.94 + for (Enum e(*this); !e.empty(); e.popFront()) {
1.95 + if (gc::IsAboutToBeFinalized(e.front().value()))
1.96 + e.removeFront();
1.97 + }
1.98 +
1.99 +#if DEBUG
1.100 + // Once we've swept, all remaining edges should stay within the
1.101 + // known-live part of the graph.
1.102 + for (Range r = Base::all(); !r.empty(); r.popFront())
1.103 + JS_ASSERT(!gc::IsAboutToBeFinalized(r.front().value()));
1.104 +#endif
1.105 + }
1.106 +};
1.107 +
1.108 +} // namespace js
1.109 +
1.110 +#endif /* jsweakcache_h */
