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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 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 */
#ifndef gc_HashUtil_h
#define gc_HashUtil_h
#include <type_traits>
#include "vm/JSContext.h"
namespace js {
* Used to add entries to a js::HashMap or HashSet where the key depends on a GC
* thing that may be moved by generational or compacting GC between the call to
* lookupForAdd() and relookupOrAdd().
template <class T>
struct DependentAddPtr {
using AddPtr = typename T::AddPtr;
using Entry = typename T::Entry;
template <class Lookup>
DependentAddPtr(const JSContext* cx, T& table, const Lookup& lookup)
: addPtr(table.lookupForAdd(lookup)),
originalGcNumber(cx->runtime()->gc.gcNumber()) {}
DependentAddPtr(DependentAddPtr&& other)
: addPtr(other.addPtr), originalGcNumber(other.originalGcNumber) {}
template <class KeyInput, class ValueInput>
bool add(JSContext* cx, T& table, const KeyInput& key,
const ValueInput& value) {
refreshAddPtr(cx, table, key);
if (!table.relookupOrAdd(addPtr, key, value)) {
return false;
return true;
template <class KeyInput>
void remove(JSContext* cx, T& table, const KeyInput& key) {
refreshAddPtr(cx, table, key);
if (addPtr) {
bool found() const { return addPtr.found(); }
explicit operator bool() const { return found(); }
const Entry& operator*() const { return *addPtr; }
const Entry* operator->() const { return &*addPtr; }
AddPtr addPtr;
const uint64_t originalGcNumber;
template <class KeyInput>
void refreshAddPtr(JSContext* cx, T& table, const KeyInput& key) {
bool gcHappened = originalGcNumber != cx->runtime()->gc.gcNumber();
if (gcHappened) {
addPtr = table.lookupForAdd(key);
DependentAddPtr() = delete;
DependentAddPtr(const DependentAddPtr&) = delete;
DependentAddPtr& operator=(const DependentAddPtr&) = delete;
template <typename T, typename Lookup>
inline auto MakeDependentAddPtr(const JSContext* cx, T& table,
const Lookup& lookup) {
using Ptr = DependentAddPtr<std::remove_reference_t<decltype(table)>>;
return Ptr(cx, table, lookup);
} // namespace js