2011-04-16 21:23:44 -07:00
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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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* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is Mozilla SpiderMonkey JavaScript 1.9 code, released
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* May 28, 2008.
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*
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* The Initial Developer of the Original Code is
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* Mozilla Foundation
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* Portions created by the Initial Developer are Copyright (C) 2009
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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* Andreas Gal <gal@mozilla.com>
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either of the GNU General Public License Version 2 or later (the "GPL"),
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* or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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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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#include "jscntxt.h"
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#include "jsobj.h"
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namespace js {
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2011-06-14 19:21:47 -07:00
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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 template parameter is a class MarkPolicy, with the following constructor:
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//
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// MarkPolicy(JSTracer *)
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//
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// and the following static member functions:
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//
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// bool keyMarked(Key &k)
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// bool valueMarked(Value &v)
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// Return true if k/v has been marked as reachable by the collector, false otherwise.
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// void markKey(Key &k, const char *description)
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// void markValue(Value &v, const char *description)
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// Mark k/v as reachable by the collector, using trc. Use description to identify
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// k/v in debugging. (markKey is used only for non-marking tracers, other code
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// using the GC heap tracing functions to map the heap for some purpose or other.)
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//
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// If omitted, this parameter defaults to js::DefaultMarkPolicy<Key, Value>, a policy
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// template with the obvious definitions for some typical SpiderMonkey type combinations.
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// A policy template holding default marking algorithms for common type combinations. This
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// provides default types for WeakMap's MarkPolicy template parameter.
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template <class Key, class Value> class DefaultMarkPolicy;
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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() : next(NULL) { }
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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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JSRuntime *rt = tracer->context->runtime;
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next = rt->gcWeakMapList;
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rt->gcWeakMapList = this;
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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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// must use their own means for cycle detection. So here we do a conservative
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// approximation: pretend all keys are live.
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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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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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private:
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// Link in a list of all the WeakMaps we have marked in this garbage collection,
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// headed by JSRuntime::gcWeakMapList.
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WeakMapBase *next;
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};
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2011-06-14 19:21:47 -07:00
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template <class Key, class Value,
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class HashPolicy = DefaultHasher<Key>,
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class MarkPolicy = DefaultMarkPolicy<Key, Value> >
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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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typedef typename Base::Range Range;
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typedef typename Base::Enum Enum;
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public:
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WeakMap(JSContext *cx) : Base(cx) { }
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private:
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void nonMarkingTrace(JSTracer *tracer) {
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MarkPolicy t(tracer);
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for (Range r = Base::all(); !r.empty(); r.popFront()) {
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t.markKey(r.front().key, "WeakMap entry key");
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t.markValue(r.front().value, "WeakMap entry value");
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}
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}
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bool markIteratively(JSTracer *tracer) {
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MarkPolicy t(tracer);
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bool markedAny = false;
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for (Range r = Base::all(); !r.empty(); r.popFront()) {
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/* If the key is alive, mark the value if needed. */
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if (!t.valueMarked(r.front().value) && t.keyMarked(r.front().key)) {
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t.markValue(r.front().value, "WeakMap entry with live key");
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/* We revived a value with children, we have to iterate again. */
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markedAny = true;
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}
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}
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return markedAny;
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}
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void sweep(JSTracer *tracer) {
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MarkPolicy t(tracer);
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for (Enum e(*this); !e.empty(); e.popFront()) {
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if (!t.keyMarked(e.front().key))
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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 edges should stay within the 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(t.keyMarked(r.front().key));
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JS_ASSERT(t.valueMarked(r.front().value));
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}
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#endif
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}
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};
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// Marking policy for maps from JSObject pointers to js::Values.
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template <>
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class DefaultMarkPolicy<JSObject *, Value> {
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private:
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JSTracer *tracer;
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public:
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DefaultMarkPolicy(JSTracer *t) : tracer(t) { }
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bool keyMarked(JSObject *k) { return !IsAboutToBeFinalized(tracer->context, k); }
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bool valueMarked(const Value &v) {
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if (v.isMarkable())
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return !IsAboutToBeFinalized(tracer->context, v.toGCThing());
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else
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return true;
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}
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void markKey(JSObject *k, const char *description) {
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js::gc::MarkObject(tracer, *k, description);
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}
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void markValue(const Value &v, const char *description) {
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js::gc::MarkValue(tracer, v, description);
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}
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};
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// The class of JavaScript WeakMap objects.
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extern Class WeakMapClass;
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2011-04-16 21:23:44 -07:00
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}
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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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