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108 lines
3.8 KiB
C++
108 lines
3.8 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=8 sts=4 et sw=4 tw=99:
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef jsweakcache_h
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#define jsweakcache_h
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#include "jscntxt.h"
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#include "gc/Marking.h"
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#include "js/HashTable.h"
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#include "vm/Runtime.h"
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namespace js {
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// A WeakCache is used to map a key to a value similar to an HashMap except
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// that its entries are garbage collected. An entry is kept as long as
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// both the key and value are marked.
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//
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// No mark function is provided with this weak container. However, this weak
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// container should take part in the sweep phase.
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template <class Key, class Value,
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class HashPolicy = DefaultHasher<Key>,
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class AllocPolicy = RuntimeAllocPolicy>
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class WeakCache : public HashMap<Key, Value, HashPolicy, AllocPolicy> {
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private:
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typedef HashMap<Key, Value, HashPolicy, AllocPolicy> Base;
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typedef typename Base::Range Range;
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typedef typename Base::Enum Enum;
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public:
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explicit WeakCache(JSRuntime *rt) : Base(rt) { }
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explicit WeakCache(JSContext *cx) : Base(cx->runtime()) { }
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public:
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// Sweep all entries which have unmarked key or value.
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void sweep(FreeOp *fop) {
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// Remove all entries whose keys/values remain unmarked.
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for (Enum e(*this); !e.empty(); e.popFront()) {
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// Checking IsMarked() may update the location of the Key (or Value).
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// Pass in a stack local, then manually update the backing heap store.
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Key k(e.front().key);
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bool isKeyDying = gc::IsAboutToBeFinalized(&k);
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if (isKeyDying || gc::IsAboutToBeFinalized(e.front().value)) {
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e.removeFront();
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} else {
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// Potentially update the location of the Key.
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// The Value had its heap addresses correctly passed to IsMarked(),
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// and therefore has already been updated if necessary.
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// e.rekeyFront(k);
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}
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}
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#if DEBUG
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// Once we've swept, all remaining edges should stay within the
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// known-live part of the graph.
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for (Range r = Base::all(); !r.empty(); r.popFront()) {
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Key k(r.front().key);
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JS_ASSERT(!gc::IsAboutToBeFinalized(&k));
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JS_ASSERT(!gc::IsAboutToBeFinalized(r.front().value));
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// Assert that IsMarked() did not perform relocation.
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JS_ASSERT(k == r.front().key);
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}
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#endif
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}
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};
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// A WeakValueCache is similar to a WeakCache, except keys are never marked.
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// This is useful for weak maps where the keys are primitive values such as uint32_t.
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template <class Key, class Value,
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class HashPolicy = DefaultHasher<Key>,
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class AllocPolicy = RuntimeAllocPolicy>
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class WeakValueCache : public HashMap<Key, Value, HashPolicy, AllocPolicy>
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{
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public:
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typedef HashMap<Key, Value, HashPolicy, AllocPolicy> Base;
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typedef typename Base::Range Range;
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typedef typename Base::Enum Enum;
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explicit WeakValueCache(JSRuntime *rt) : Base(rt) { }
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explicit WeakValueCache(JSContext *cx) : Base(cx->runtime()) { }
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public:
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// Sweep all entries which have unmarked key or value.
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void sweep(FreeOp *fop) {
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// Remove all entries whose values remain unmarked.
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for (Enum e(*this); !e.empty(); e.popFront()) {
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if (gc::IsAboutToBeFinalized(e.front().value()))
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e.removeFront();
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}
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#if DEBUG
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// Once we've swept, all remaining edges should stay within the
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// known-live part of the graph.
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for (Range r = Base::all(); !r.empty(); r.popFront())
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JS_ASSERT(!gc::IsAboutToBeFinalized(r.front().value()));
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#endif
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}
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};
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} // namespace js
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#endif /* jsweakcache_h */
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