gecko/js/ipc/JavaScriptShared.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sw=4 et tw=80:
 *
 * 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/. */

#ifndef mozilla_jsipc_JavaScriptShared_h__
#define mozilla_jsipc_JavaScriptShared_h__

#include "mozilla/dom/DOMTypes.h"
#include "mozilla/jsipc/PJavaScript.h"
#include "nsJSUtils.h"
#include "nsFrameMessageManager.h"

namespace mozilla {
namespace jsipc {

class ObjectId {
  public:
    // Use 47 bits at most, to be safe, since jsval privates are encoded as
    // doubles. See bug 1065811 comment 12 for an explanation.
    static const size_t SERIAL_NUMBER_BITS = 47;
    static const size_t FLAG_BITS = 1;
    static const uint64_t SERIAL_NUMBER_MAX = (uint64_t(1) << SERIAL_NUMBER_BITS) - 1;

    explicit ObjectId(uint64_t serialNumber, bool hasXrayWaiver)
      : serialNumber_(serialNumber), hasXrayWaiver_(hasXrayWaiver)
    {
        if (MOZ_UNLIKELY(serialNumber == 0 || serialNumber > SERIAL_NUMBER_MAX))
            MOZ_CRASH("Bad CPOW Id");
    }

    bool operator==(const ObjectId &other) const {
        bool equal = serialNumber() == other.serialNumber();
        MOZ_ASSERT_IF(equal, hasXrayWaiver() == other.hasXrayWaiver());
        return equal;
    }

    bool isNull() { return !serialNumber_; }

    uint64_t serialNumber() const { return serialNumber_; }
    bool hasXrayWaiver() const { return hasXrayWaiver_; }
    uint64_t serialize() const {
        MOZ_ASSERT(serialNumber(), "Don't send a null ObjectId over IPC");
        return uint64_t((serialNumber() << FLAG_BITS) | ((hasXrayWaiver() ? 1 : 0) << 0));
    }

    static ObjectId nullId() { return ObjectId(); }
    static ObjectId deserialize(uint64_t data) {
        return ObjectId(data >> FLAG_BITS, data & 1);
    }

  private:
    ObjectId() : serialNumber_(0), hasXrayWaiver_(false) {}

    uint64_t serialNumber_ : SERIAL_NUMBER_BITS;
    bool hasXrayWaiver_ : 1;
};

class JavaScriptShared;

class CpowIdHolder : public CpowHolder
{
  public:
    CpowIdHolder(JavaScriptShared *js, const InfallibleTArray<CpowEntry> &cpows)
      : js_(js),
        cpows_(cpows)
    {
    }

    bool ToObject(JSContext *cx, JS::MutableHandleObject objp);

  private:
    JavaScriptShared *js_;
    const InfallibleTArray<CpowEntry> &cpows_;
};

// DefaultHasher<T> requires that T coerce to an integral type. We could make
// ObjectId do that, but doing so would weaken our type invariants, so we just
// reimplement it manually.
struct ObjectIdHasher
{
    typedef ObjectId Lookup;
    static js::HashNumber hash(const Lookup &l) {
        return l.serialize();
    }
    static bool match(const ObjectId &k, const ObjectId &l) {
        return k == l;
    }
    static void rekey(ObjectId &k, const ObjectId& newKey) {
        k = newKey;
    }
};

// Map ids -> JSObjects
class IdToObjectMap
{
    typedef js::HashMap<ObjectId, JS::Heap<JSObject *>, ObjectIdHasher, js::SystemAllocPolicy> Table;

  public:
    IdToObjectMap();

    bool init();
    void trace(JSTracer *trc);
    void sweep();

    bool add(ObjectId id, JSObject *obj);
    JSObject *find(ObjectId id);
    void remove(ObjectId id);

  private:
    Table table_;
};

// Map JSObjects -> ids
class ObjectToIdMap
{
    typedef js::PointerHasher<JSObject *, 3> Hasher;
    typedef js::HashMap<JSObject *, ObjectId, Hasher, js::SystemAllocPolicy> Table;

  public:
    ObjectToIdMap();
    ~ObjectToIdMap();

    bool init();
    void trace(JSTracer *trc);
    void sweep();

    bool add(JSContext *cx, JSObject *obj, ObjectId id);
    ObjectId find(JSObject *obj);
    void remove(JSObject *obj);

  private:
    static void keyMarkCallback(JSTracer *trc, JSObject *key, void *data);

    Table *table_;
};

class Logging;

class JavaScriptShared
{
  public:
    explicit JavaScriptShared(JSRuntime *rt);
    virtual ~JavaScriptShared() {}

    bool init();

    void decref();
    void incref();

    bool Unwrap(JSContext *cx, const InfallibleTArray<CpowEntry> &aCpows, JS::MutableHandleObject objp);
    bool Wrap(JSContext *cx, JS::HandleObject aObj, InfallibleTArray<CpowEntry> *outCpows);

  protected:
    bool toVariant(JSContext *cx, JS::HandleValue from, JSVariant *to);
    bool fromVariant(JSContext *cx, const JSVariant &from, JS::MutableHandleValue to);

    bool fromDescriptor(JSContext *cx, JS::Handle<JSPropertyDescriptor> desc,
                        PPropertyDescriptor *out);
    bool toDescriptor(JSContext *cx, const PPropertyDescriptor &in,
                      JS::MutableHandle<JSPropertyDescriptor> out);

    bool convertIdToGeckoString(JSContext *cx, JS::HandleId id, nsString *to);
    bool convertGeckoStringToId(JSContext *cx, const nsString &from, JS::MutableHandleId id);

    virtual bool toObjectVariant(JSContext *cx, JSObject *obj, ObjectVariant *objVarp) = 0;
    virtual JSObject *fromObjectVariant(JSContext *cx, ObjectVariant objVar) = 0;

    static void ConvertID(const nsID &from, JSIID *to);
    static void ConvertID(const JSIID &from, nsID *to);

    JSObject *findCPOWById(const ObjectId &objId) {
        return cpows_.find(objId);
    }
    JSObject *findObjectById(JSContext *cx, const ObjectId &objId);

    static bool LoggingEnabled() { return sLoggingEnabled; }
    static bool StackLoggingEnabled() { return sStackLoggingEnabled; }

    friend class Logging;

    virtual bool isParent() = 0;

    virtual JSObject *scopeForTargetObjects() = 0;

  protected:
    JSRuntime *rt_;
    uintptr_t refcount_;

    IdToObjectMap objects_;
    IdToObjectMap cpows_;

    uint64_t nextSerialNumber_;

    // CPOW references can be weak, and any object we store in a map may be
    // GCed (at which point the CPOW will report itself "dead" to the owner).
    // This means that we don't want to store any js::Wrappers in the CPOW map,
    // because CPOW will die if the wrapper is GCed, even if the underlying
    // object is still alive.
    //
    // This presents a tricky situation for Xray waivers, since they're normally
    // represented as a special same-compartment wrapper. We have to strip them
    // off before putting them in the id-to-object and object-to-id maps, so we
    // need a way of distinguishing them at lookup-time.
    //
    // For the id-to-object map, we encode waiver-or-not information into the id
    // itself, which lets us do the right thing when accessing the object.
    //
    // For the object-to-id map, we just keep two maps, one for each type.
    ObjectToIdMap unwaivedObjectIds_;
    ObjectToIdMap waivedObjectIds_;
    ObjectToIdMap &objectIdMap(bool waiver) {
        return waiver ? waivedObjectIds_ : unwaivedObjectIds_;
    }

    static bool sLoggingInitialized;
    static bool sLoggingEnabled;
    static bool sStackLoggingEnabled;
};

} // namespace jsipc
} // namespace mozilla

#endif