有人尝试过 C++ 的事务内存吗？

发布于 2024-07-05 14:34:33 字数 121 浏览 8 评论 0原文

我正在查看英特尔的“whatif”网站及其事务内存编译器（每个线程必须进行原子提交或回滚系统内存，就像数据库一样）。

这似乎是一种替代锁和互斥体的有前途的方法，但我找不到很多推荐。这里有人有任何意见吗？

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鱼忆七猫命九 2024-07-12 14:34:33

我基于一些函数式编程思想构建了组合 STM 库。它不需要任何编译器支持（除了它使用 C++17），也不会带来新的语法。一般来说，它采用Haskell的STM库的接口。

所以，我的库有几个很好的属性：

单子组合。每个事务都是名为 STML 的自定义 monad 内的计算。您可以将单子交易组合成更大的单子交易。
事务与数据模型分离。您可以使用事务变量 (TVars) 构建并发数据模型，并对其运行事务。
有重试组合器。它允许您重新运行事务。对于构建简短且易于理解的交易非常有用。
有不同的一元组合器可以快速表达计算。
有上下文。每个计算都应该在某个上下文中运行，而不是在全局运行时中运行。因此，如果您需要多个独立的 STM 集群，则可以拥有许多不同的上下文。
从概念上讲，实现非常简单。至少，Haskell 中的参考实现是这样，但我不得不重新发明几种 C++ 方法由于缺乏函数式编程的良好支持而导致的实现。

即使我们认为它是实验性的，该库也显示出非常好的稳定性和鲁棒性。此外，我的方法为通过性能、功能、全面性等来改进库提供了很多可能性。

为了演示其工作，我解决了Dining Philosophers 任务。您可以在下面的链接中找到该代码。交易示例：

STML<bool> takeFork(const TVar<Fork>& tFork)
{
    STML<bool> alreadyTaken = withTVar(tFork, isForkTaken);
    STML<Unit> takenByUs    = modifyTVar(tFork, setForkTaken);
    STML<bool> success      = sequence(takenByUs, pure(true));
    STML<bool> fail         = pure(false);
    STML<bool> result       = ifThenElse(alreadyTaken, fail, success);
    return result;
};

更新
我写了一个教程，您可以在此处找到它。

I've built the combinatorial STM library on top of some functional programming ideas. It doesn't require any compiler support (except it uses C++17), doesn't bring a new syntax. In general, it adopts the interface of the STM library from Haskell.

So, my library has several nice properties:

Monadically combinatorial. Every transaction is a computation inside the custom monad named STML. You can combine monadic transactions into more big monadic transactions.
Transactions are separated from data model. You construct your concurrent data model with transactional variables (TVars) and run transactions over it.
There is retry combinator. It allows you to rerun the transaction. Very useful to build short and understandable transactions.
There are different monadic combinators to express computations shortly.
There is Context. Every computation should be run in some context, not in the global runtime. So you can have many different contexts if you need several independent STM clusters.
The implementation is quite simple conceptually. At least, the reference implementation in Haskell is so, but I had to reinvent several approaches for C++ implementation due to the lack of a good support of Functional Programming.

The library shows very nice stability and robustness, even if we consider it experimental. Moreover, my approach opens a lot of possibilities to improve the library by performance, features, comprehensiveness, etc.

To demonstrate its work, I've solved the Dining Philosophers task. You can find the code in the links below. Sample transaction:

STML<bool> takeFork(const TVar<Fork>& tFork)
{
    STML<bool> alreadyTaken = withTVar(tFork, isForkTaken);
    STML<Unit> takenByUs    = modifyTVar(tFork, setForkTaken);
    STML<bool> success      = sequence(takenByUs, pure(true));
    STML<bool> fail         = pure(false);
    STML<bool> result       = ifThenElse(alreadyTaken, fail, success);
    return result;
};

UPDATE
I've wrote a tutorial, you can find it here.

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