I wasn't aware of the std::atomic variables but was aware about the std::mutex (weird right!) provided by the standard; however one thing caught my eye: there are two seemingly-same(to me) atomic types provided by the standard, listed below:
我不知道std::原子变量，但知道标准提供的std:::mutex(奇怪的右!)然而，有一件事引起了我的注意:在我看来，标准提供的原子类型有两种:
-
std::atomic<bool>typestd::原子< bool >类型
-
std::atomic_flagtypestd::atomic_flag类型
Also it is mentioned with the example of std::atomic_flag type -
还有一个std::atomic_flag类型-的例子
std::atomic_flag is an atomic boolean type. Unlike all specializations of std::atomic, it is guaranteed to be lock-free. Unlike std::atomic, std::atomic_flag does not provide load or store operations.
atomic_flag是一种布尔类型。与std::atomic的所有专门化不同，它保证是无锁的。不同于std::原子，std::atomic_flag不提供负载或存储操作。
which I fail to understand. Is std::atomic bool type not guaranteed to be lock-free? Then it's not atomic or what?
我不明白。std::原子bool类型不保证是无锁的吗?那么它不是原子还是什么?
So what's the difference between the two and when should I use which?
那么这两者之间的区别是什么?
2 个解决方案
#1
22
std::atomic bool type not guranteed to be lock-free?
原子bool类型不保证无锁?
Correct. std::atomic may be implemented using locks.
正确的。可以使用锁实现原子化。
then it's not atomic or what?
那么它不是原子还是什么?
std::atomic is atomic whether it has been implemented using locks, or without. std::atomic_flag is guaranteed to be implemented without using locks.
原子是原子的，无论是否使用锁实现。std::atomic_flag可以在不使用锁的情况下实现。
So what's the difference b/w two
b/w 2的差是多少
The primary difference besides the lock-free guarantee is:
除了无锁保证外，主要的区别是:
std::atomic_flagdoes not provide load or store operations.atomic_flag不提供加载或存储操作。
and when should I use which?
什么时候用哪个?
Usually, you will want to use std::atomic<bool> when you need an atomic boolean variable. std::atomic_flag is a low level structure that can be used to implement custom atomic structures.
通常，当您需要一个原子布尔变量时，您需要使用std::atomic
#2
18
std::atomic<T> guarantees that accesses to the variable will be atomic. It however does not says how is the atomicity achieved. It can be using lock-free variable, or using a lock. The actual implementation depends on your target architecture and the type T.
原子
std::atomic_flag on the other hand is guaranteed to be implemented using a lock-free technique.
另一方面，atomic_flag保证使用无锁技术来实现。
#1
22
std::atomic bool type not guranteed to be lock-free?
原子bool类型不保证无锁?
Correct. std::atomic may be implemented using locks.
正确的。可以使用锁实现原子化。
then it's not atomic or what?
那么它不是原子还是什么?
std::atomic is atomic whether it has been implemented using locks, or without. std::atomic_flag is guaranteed to be implemented without using locks.
原子是原子的，无论是否使用锁实现。std::atomic_flag可以在不使用锁的情况下实现。
So what's the difference b/w two
b/w 2的差是多少
The primary difference besides the lock-free guarantee is:
除了无锁保证外，主要的区别是:
std::atomic_flagdoes not provide load or store operations.atomic_flag不提供加载或存储操作。
and when should I use which?
什么时候用哪个?
Usually, you will want to use std::atomic<bool> when you need an atomic boolean variable. std::atomic_flag is a low level structure that can be used to implement custom atomic structures.
通常，当您需要一个原子布尔变量时，您需要使用std::atomic
#2
18
std::atomic<T> guarantees that accesses to the variable will be atomic. It however does not says how is the atomicity achieved. It can be using lock-free variable, or using a lock. The actual implementation depends on your target architecture and the type T.
原子
std::atomic_flag on the other hand is guaranteed to be implemented using a lock-free technique.
另一方面，atomic_flag保证使用无锁技术来实现。