зеркало из https://github.com/mozilla/gecko-dev.git
260 строки
10 KiB
C++
260 строки
10 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 jsweakmap_h
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#define jsweakmap_h
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#include "jscompartment.h"
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#include "jsfriendapi.h"
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#include "jsobj.h"
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#include "gc/Marking.h"
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#include "js/HashTable.h"
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namespace js {
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// A subclass template of js::HashMap whose keys and values may be garbage-collected. When
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// a key is collected, the table entry disappears, dropping its reference to the value.
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//
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// More precisely:
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//
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// A WeakMap entry is collected if and only if either the WeakMap or the entry's key
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// is collected. If an entry is not collected, it remains in the WeakMap and it has a
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// strong reference to the value.
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//
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// You must call this table's 'trace' method when the object of which it is a part is
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// reached by the garbage collection tracer. Once a table is known to be live, the
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// implementation takes care of the iterative marking needed for weak tables and removing
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// table entries when collection is complete.
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// The value for the next pointer for maps not in the map list.
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static WeakMapBase * const WeakMapNotInList = reinterpret_cast<WeakMapBase *>(1);
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typedef Vector<WeakMapBase *, 0, SystemAllocPolicy> WeakMapVector;
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// Common base class for all WeakMap specializations. The collector uses this to call
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// their markIteratively and sweep methods.
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class WeakMapBase {
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public:
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WeakMapBase(JSObject *memOf, JSCompartment *c);
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virtual ~WeakMapBase();
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void trace(JSTracer *tracer) {
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if (IS_GC_MARKING_TRACER(tracer)) {
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// We don't do anything with a WeakMap at trace time. Rather, we wait until as
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// many keys as possible have been marked, and add ourselves to the list of
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// known-live WeakMaps to be scanned in the iterative marking phase, by
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// markAllIteratively.
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JS_ASSERT(tracer->eagerlyTraceWeakMaps == DoNotTraceWeakMaps);
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// Add ourselves to the list if we are not already in the list. We can already
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// be in the list if the weak map is marked more than once due delayed marking.
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if (next == WeakMapNotInList) {
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next = compartment->gcWeakMapList;
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compartment->gcWeakMapList = this;
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}
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} else {
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// If we're not actually doing garbage collection, the keys won't be marked
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// nicely as needed by the true ephemeral marking algorithm --- custom tracers
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// such as the cycle collector must use their own means for cycle detection.
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// So here we do a conservative approximation: pretend all keys are live.
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if (tracer->eagerlyTraceWeakMaps == DoNotTraceWeakMaps)
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return;
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nonMarkingTraceValues(tracer);
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if (tracer->eagerlyTraceWeakMaps == TraceWeakMapKeysValues)
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nonMarkingTraceKeys(tracer);
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}
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}
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// Garbage collector entry points.
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// Check all weak maps in a compartment that have been marked as live in this garbage
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// collection, and mark the values of all entries that have become strong references
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// to them. Return true if we marked any new values, indicating that we need to make
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// another pass. In other words, mark my marked maps' marked members' mid-collection.
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static bool markCompartmentIteratively(JSCompartment *c, JSTracer *tracer);
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// Remove entries whose keys are dead from all weak maps in a compartment marked as
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// live in this garbage collection.
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static void sweepCompartment(JSCompartment *c);
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// Trace all delayed weak map bindings. Used by the cycle collector.
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static void traceAllMappings(WeakMapTracer *tracer);
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void check() { JS_ASSERT(next == WeakMapNotInList); }
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// Remove everything from the weak map list for a compartment.
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static void resetCompartmentWeakMapList(JSCompartment *c);
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// Save the live weak map list for a compartment, appending the data to a vector.
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static bool saveCompartmentWeakMapList(JSCompartment *c, WeakMapVector &vector);
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// Restore live weak map lists for multiple compartments from a vector.
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static void restoreCompartmentWeakMapLists(WeakMapVector &vector);
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// Remove a weakmap from the live weakmaps list
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static void removeWeakMapFromList(WeakMapBase *weakmap);
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protected:
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// Instance member functions called by the above. Instantiations of WeakMap override
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// these with definitions appropriate for their Key and Value types.
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virtual void nonMarkingTraceKeys(JSTracer *tracer) = 0;
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virtual void nonMarkingTraceValues(JSTracer *tracer) = 0;
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virtual bool markIteratively(JSTracer *tracer) = 0;
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virtual void sweep() = 0;
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virtual void traceMappings(WeakMapTracer *tracer) = 0;
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// Object that this weak map is part of, if any.
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JSObject *memberOf;
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// Compartment that this weak map is part of.
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JSCompartment *compartment;
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private:
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// Link in a list of WeakMaps to mark iteratively and sweep in this garbage
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// collection, headed by JSCompartment::gcWeakMapList. The last element of
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// the list has nullptr as its next. Maps not in the list have
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// WeakMapNotInList as their next. We must distinguish these cases to
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// avoid creating infinite lists when a weak map gets traced twice due to
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// delayed marking.
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WeakMapBase *next;
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};
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template <class Key, class Value,
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class HashPolicy = DefaultHasher<Key> >
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class WeakMap : public HashMap<Key, Value, HashPolicy, RuntimeAllocPolicy>, public WeakMapBase
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{
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public:
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typedef HashMap<Key, Value, HashPolicy, RuntimeAllocPolicy> Base;
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typedef typename Base::Enum Enum;
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typedef typename Base::Lookup Lookup;
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typedef typename Base::Range Range;
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explicit WeakMap(JSContext *cx, JSObject *memOf = nullptr)
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: Base(cx->runtime()), WeakMapBase(memOf, cx->compartment()) { }
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private:
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bool markValue(JSTracer *trc, Value *x) {
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if (gc::IsMarked(x))
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return false;
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gc::Mark(trc, x, "WeakMap entry value");
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JS_ASSERT(gc::IsMarked(x));
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return true;
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}
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void nonMarkingTraceKeys(JSTracer *trc) {
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for (Enum e(*this); !e.empty(); e.popFront()) {
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Key key(e.front().key);
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gc::Mark(trc, &key, "WeakMap entry key");
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if (key != e.front().key)
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entryMoved(e, key);
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}
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}
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void nonMarkingTraceValues(JSTracer *trc) {
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for (Range r = Base::all(); !r.empty(); r.popFront())
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gc::Mark(trc, &r.front().value, "WeakMap entry value");
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}
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bool keyNeedsMark(JSObject *key) {
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if (JSWeakmapKeyDelegateOp op = key->getClass()->ext.weakmapKeyDelegateOp) {
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JSObject *delegate = op(key);
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/*
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* Check if the delegate is marked with any color to properly handle
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* gray marking when the key's delegate is black and the map is
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* gray.
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*/
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return delegate && gc::IsObjectMarked(&delegate);
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}
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return false;
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}
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bool keyNeedsMark(gc::Cell *cell) {
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return false;
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}
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bool markIteratively(JSTracer *trc) {
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bool markedAny = false;
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for (Enum e(*this); !e.empty(); e.popFront()) {
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/* If the entry is live, ensure its key and value are marked. */
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Key key(e.front().key);
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if (gc::IsMarked(const_cast<Key *>(&key))) {
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if (markValue(trc, &e.front().value))
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markedAny = true;
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if (e.front().key != key)
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entryMoved(e, key);
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} else if (keyNeedsMark(key)) {
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gc::Mark(trc, const_cast<Key *>(&key), "proxy-preserved WeakMap entry key");
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if (e.front().key != key)
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entryMoved(e, key);
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gc::Mark(trc, &e.front().value, "WeakMap entry value");
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markedAny = true;
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}
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key.unsafeSet(nullptr);
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}
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return markedAny;
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}
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void sweep() {
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/* Remove all entries whose keys remain unmarked. */
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for (Enum e(*this); !e.empty(); e.popFront()) {
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Key k(e.front().key);
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if (gc::IsAboutToBeFinalized(&k))
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e.removeFront();
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else if (k != e.front().key)
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entryMoved(e, k);
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}
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/*
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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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*/
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assertEntriesNotAboutToBeFinalized();
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}
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/* memberOf can be nullptr, which means that the map is not part of a JSObject. */
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void traceMappings(WeakMapTracer *tracer) {
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for (Range r = Base::all(); !r.empty(); r.popFront()) {
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gc::Cell *key = gc::ToMarkable(r.front().key);
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gc::Cell *value = gc::ToMarkable(r.front().value);
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if (key && value) {
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tracer->callback(tracer, memberOf,
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key, gc::TraceKind(r.front().key),
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value, gc::TraceKind(r.front().value));
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}
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}
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}
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/* Rekey an entry when moved, ensuring we do not trigger barriers. */
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void entryMoved(Enum &eArg, const Key &k) {
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typedef typename HashMap<typename Unbarriered<Key>::type,
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typename Unbarriered<Value>::type,
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typename Unbarriered<HashPolicy>::type,
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RuntimeAllocPolicy>::Enum UnbarrieredEnum;
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UnbarrieredEnum &e = reinterpret_cast<UnbarrieredEnum &>(eArg);
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e.rekeyFront(reinterpret_cast<const typename Unbarriered<Key>::type &>(k));
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}
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protected:
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void assertEntriesNotAboutToBeFinalized() {
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#if DEBUG
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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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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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} /* namespace js */
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extern JSObject *
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js_InitWeakMapClass(JSContext *cx, js::HandleObject obj);
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#endif /* jsweakmap_h */
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