ObjectToIDMap.h

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/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */


/**
 * Providing a map-like structure with JSObject pointers (actually their hash) as keys
 * with correct garbage collection handling (JSObjects can move in memory).
 *
 * The code in this class was copied from here and modified to work in our environment.
 *  * https://mxr.mozilla.org/mozilla-esr38/source/js/ipc/JavaScriptShared.h
 *  * https://mxr.mozilla.org/mozilla-esr38/source/js/ipc/JavaScriptShared.cpp
 *
 * When updating SpiderMonkey, you most likely have to reintegrate an updated version
 * of the class(es) in this file. The best way is probably to get a diff between the
 * original files and integrate that because this file is heavily modified from the
 * original version.
 */

#ifndef INCLUDED_OBJECTTOIDMAP
#define INCLUDED_OBJECTTOIDMAP

#include "scriptinterface/ScriptRuntime.h"
#include "scriptinterface/ScriptTypes.h"
#include <stdint.h>

// Map JSObjects -> ids
template <typename T>
class ObjectIdCache
{
    typedef js::PointerHasher<JSObject*, 3> Hasher;
    typedef js::HashMap<JSObject*, T, Hasher, js::SystemAllocPolicy> Table;

    NONCOPYABLE(ObjectIdCache);

public:
    ObjectIdCache(shared_ptr<ScriptRuntime> rt)
        : table_(nullptr), m_rt(rt)
    {
    }

    ~ObjectIdCache()
    {
        if (table_)
        {
            m_rt->AddDeferredFinalizationObject(std::shared_ptr<void>((void*)table_, DeleteTable));
            table_ = nullptr;
            JS_RemoveExtraGCRootsTracer(m_rt->m_rt, ObjectIdCache::Trace, this);
        }
    }

    bool init()
    {
        if (table_)
            return true;

        table_ = new Table(js::SystemAllocPolicy());
        JS_AddExtraGCRootsTracer(m_rt->m_rt, ObjectIdCache::Trace, this);
        return table_ && table_->init(32);
    }

    void trace(JSTracer* trc)
    {
        for (typename Table::Enum e(*table_); !e.empty(); e.popFront())
        {
            JSObject* obj = e.front().key();
            JS_CallUnbarrieredObjectTracer(trc, &obj, "ipc-object");
            if (obj != e.front().key())
                e.rekeyFront(obj);
        }
    }

// TODO sweep?

    bool find(JSObject* obj, T& ret)
    {
        typename Table::Ptr p = table_->lookup(obj);
        if (!p)
            return false;
        ret = p->value();
        return true;
    }

    bool add(JSContext* cx, JSObject* obj, T id)
    {
        if (!table_->put(obj, id))
            return false;
        JS_StoreObjectPostBarrierCallback(cx, keyMarkCallback, obj, table_);
        return true;
    }

    void remove(JSObject* obj)
    {
        table_->remove(obj);
    }

// TODO clear?

    bool empty()
    {
        return table_->empty();
    }

    bool has(JSObject* obj)
    {
        return table_->has(obj);
    }

private:
    static void keyMarkCallback(JSTracer* trc, JSObject* key, void* data)
    {
        Table* table = static_cast<Table*>(data);
        JSObject* prior = key;
        JS_CallUnbarrieredObjectTracer(trc, &key, "ObjectIdCache::table_ key");
        table->rekeyIfMoved(prior, key);
    }

    static void Trace(JSTracer* trc, void* data)
    {
        reinterpret_cast<ObjectIdCache*>(data)->trace(trc);
    }

    static void DeleteTable(void* table)
    {
        delete (Table*)table;
    }

    shared_ptr<ScriptRuntime> m_rt;
    Table* table_;
};

#endif // INCLUDED_OBJECTTOIDMAP