2011-04-17 08:23:44 +04:00
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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=4 sw=4 et tw=99:
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*
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2012-05-21 15:12:37 +04:00
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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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2011-04-17 08:23:44 +04:00
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#ifndef jsweakmap_h___
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#define jsweakmap_h___
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#include "jsapi.h"
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2011-11-24 16:35:56 +04:00
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#include "jsfriendapi.h"
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2011-04-17 08:23:44 +04:00
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#include "jscntxt.h"
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#include "jsobj.h"
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2012-05-02 01:30:18 +04:00
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#include "gc/Marking.h"
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2011-10-05 02:33:00 +04:00
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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 'mark' 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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//
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// You may provide your own MarkPolicy class to specify how keys and values are marked; a
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// policy template provides default definitions for some common key/value type
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// combinations.
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//
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// Details:
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//
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// The interface is as for a js::HashMap, with the following additions:
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//
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// - You must call the WeakMap's 'trace' member function when you discover that the map is
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// part of a live object. (You'll typically call this from the containing type's 'trace'
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// function.)
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//
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// - There is no AllocPolicy parameter; these are used with our garbage collector, so
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// RuntimeAllocPolicy is hard-wired.
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//
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// - Optional fourth and fifth parameters are the MarkPolicies for the key and value type.
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// A MarkPolicy has the constructor:
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//
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// MarkPolicy(JSTracer *)
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//
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// and the following member functions:
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//
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// bool isMarked(const Type &x)
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// Return true if x has been marked as live by the garbage collector.
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//
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// bool mark(Type &x)
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// Return false if x is already marked. Otherwise, mark x and return true.
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//
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// If omitted, the MarkPolicy parameter defaults to js::DefaultMarkPolicy<Type>,
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// a policy template with the obvious definitions for some typical
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// SpiderMonkey type combinations.
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2012-01-06 23:30:09 +04:00
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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) : memberOf(memOf), next(WeakMapNotInList) { }
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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);
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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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JSRuntime *rt = tracer->runtime;
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next = rt->gcWeakMapList;
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rt->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)
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nonMarkingTrace(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 that have been marked as live so far 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 markAllIteratively(JSTracer *tracer);
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// Remove entries whose keys are dead from all weak maps marked as live in this
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// garbage collection.
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static void sweepAll(JSTracer *tracer);
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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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2012-02-18 02:35:20 +04:00
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void check() { JS_ASSERT(next == WeakMapNotInList); }
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// Remove everything from the live weak map list.
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static void resetWeakMapList(JSRuntime *rt);
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// Save and restore the live weak map list to a vector.
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static bool saveWeakMapList(JSRuntime *rt, WeakMapVector &vector);
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static void restoreWeakMapList(JSRuntime *rt, WeakMapVector &vector);
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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 nonMarkingTrace(JSTracer *tracer) = 0;
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virtual bool markIteratively(JSTracer *tracer) = 0;
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virtual void sweep(JSTracer *tracer) = 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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private:
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2011-06-21 03:26:05 +04:00
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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 JSRuntime::gcWeakMapList. The last element of the list
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// has NULL as its next. Maps not in the list have WeakMapNotInList as their
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// next. We must distinguish these cases to avoid creating infinite lists
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// when a weak map gets traced twice due to 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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private:
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typedef HashMap<Key, Value, HashPolicy, RuntimeAllocPolicy> Base;
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public:
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typedef typename Base::Enum Enum;
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typedef typename Base::Range Range;
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explicit WeakMap(JSRuntime *rt, JSObject *memOf=NULL) : Base(rt), WeakMapBase(memOf) { }
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explicit WeakMap(JSContext *cx, JSObject *memOf=NULL) : Base(cx), WeakMapBase(memOf) { }
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/* Use with caution, as result can be affected by garbage collection. */
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Range nondeterministicAll() {
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return Base::all();
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}
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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");
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return true;
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}
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2011-10-26 03:07:42 +04:00
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void nonMarkingTrace(JSTracer *trc) {
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for (Range r = Base::all(); !r.empty(); r.popFront())
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markValue(trc, &r.front().value);
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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 k(e.front().key);
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bool keyIsMarked = gc::IsMarked(&k);
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if (keyIsMarked) {
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if (markValue(trc, &e.front().value))
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markedAny = true;
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e.rekeyFront(k);
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}
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}
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return markedAny;
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}
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2011-10-26 03:07:42 +04:00
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void sweep(JSTracer *trc) {
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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::IsMarked(&k))
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e.removeFront();
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}
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2011-06-29 13:27:47 +04:00
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2011-06-15 06:21:47 +04:00
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#if DEBUG
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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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for (Range r = Base::all(); !r.empty(); r.popFront()) {
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Key k(r.front().key);
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Value v(r.front().value);
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JS_ASSERT(gc::IsMarked(&k));
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JS_ASSERT(gc::IsMarked(&v));
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JS_ASSERT(k == r.front().key);
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JS_ASSERT(v == r.front().value);
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2011-06-15 06:21:47 +04:00
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}
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#endif
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}
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2011-11-24 16:35:56 +04:00
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2012-04-09 22:42:04 +04:00
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/* memberOf can be NULL, which means that the map is not part of a JSObject. */
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2012-03-30 04:35:46 +04:00
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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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2011-11-24 16:35:56 +04:00
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}
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};
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2012-03-30 04:35:46 +04:00
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} /* namespace js */
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2011-04-17 08:23:44 +04:00
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extern JSObject *
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js_InitWeakMapClass(JSContext *cx, JSObject *obj);
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#endif
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