forked from mirrors/gecko-dev
e8f9ed23ec
Prior to this patch, one would need to manually instantiate a copy of a string from a preference on the main thread in order to access it in a threadsafe manner on another thread. This patch adds support for a `DataMutexString` threadsafe type for mirror: always type StaticPrefs, and works similarly to the existing atomic types. Differential Revision: https://phabricator.services.mozilla.com/D153829
130 lines
3.7 KiB
C++
130 lines
3.7 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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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 file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef DataMutex_h__
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#define DataMutex_h__
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#include <utility>
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#include "mozilla/Mutex.h"
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#include "mozilla/StaticMutex.h"
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namespace mozilla {
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// A template to wrap a type with a mutex so that accesses to the type's
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// data are required to take the lock before accessing it. This ensures
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// that a mutex is explicitly associated with the data that it protects,
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// and makes it impossible to access the data without first taking the
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// associated mutex.
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//
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// This is based on Rust's std::sync::Mutex, which operates under the
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// strategy of locking data, rather than code.
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//
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// Examples:
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//
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// DataMutex<uint32_t> u32DataMutex(1, "u32DataMutex");
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// auto x = u32DataMutex.Lock();
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// *x = 4;
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// assert(*x, 4u);
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//
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// DataMutex<nsTArray<uint32_t>> arrayDataMutex("arrayDataMutex");
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// auto a = arrayDataMutex.Lock();
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// auto& x = a.ref();
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// x.AppendElement(1u);
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// assert(x[0], 1u);
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//
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template <typename T, typename MutexType>
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class DataMutexBase {
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public:
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template <typename V>
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class MOZ_STACK_CLASS AutoLockBase {
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public:
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V* operator->() const& { return &ref(); }
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V* operator->() const&& = delete;
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V& operator*() const& { return ref(); }
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V& operator*() const&& = delete;
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// Like RefPtr, make this act like its underlying raw pointer type
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// whenever it is used in a context where a raw pointer is expected.
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operator V*() const& { return &ref(); }
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// Like RefPtr, don't allow implicit conversion of temporary to raw pointer.
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operator V*() const&& = delete;
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V& ref() const& {
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MOZ_ASSERT(mOwner);
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return mOwner->mValue;
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}
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V& ref() const&& = delete;
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AutoLockBase(AutoLockBase&& aOther) : mOwner(aOther.mOwner) {
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aOther.mOwner = nullptr;
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}
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~AutoLockBase() {
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if (mOwner) {
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mOwner->mMutex.Unlock();
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mOwner = nullptr;
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}
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}
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private:
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friend class DataMutexBase;
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AutoLockBase(const AutoLockBase& aOther) = delete;
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explicit AutoLockBase(DataMutexBase<T, MutexType>* aDataMutex)
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: mOwner(aDataMutex) {
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MOZ_ASSERT(!!mOwner);
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mOwner->mMutex.Lock();
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}
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DataMutexBase<T, MutexType>* mOwner;
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};
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using AutoLock = AutoLockBase<T>;
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using ConstAutoLock = AutoLockBase<const T>;
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explicit DataMutexBase(const char* aName) : mMutex(aName) {}
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DataMutexBase(T&& aValue, const char* aName)
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: mMutex(aName), mValue(std::move(aValue)) {}
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AutoLock Lock() { return AutoLock(this); }
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ConstAutoLock ConstLock() { return ConstAutoLock(this); }
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const MutexType& Mutex() const { return mMutex; }
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private:
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MutexType mMutex;
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T mValue;
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};
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// Craft a version of StaticMutex that takes a const char* in its ctor.
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// We need this so it works interchangeably with Mutex which requires a const
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// char* aName in its ctor.
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class StaticMutexNameless : public StaticMutex {
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public:
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explicit StaticMutexNameless(const char* aName) : StaticMutex() {}
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private:
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// Disallow copy construction, `=`, `new`, and `delete` like BaseStaticMutex.
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#ifdef DEBUG
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StaticMutexNameless(StaticMutexNameless& aOther);
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#endif // DEBUG
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StaticMutexNameless& operator=(StaticMutexNameless* aRhs);
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static void* operator new(size_t) noexcept(true);
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static void operator delete(void*);
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};
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template <typename T>
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using DataMutex = DataMutexBase<T, Mutex>;
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template <typename T>
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using StaticDataMutex = DataMutexBase<T, StaticMutexNameless>;
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} // namespace mozilla
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#endif // DataMutex_h__
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