How to acquire a lock in C++?

Question

Can any one helps me to understand how to lock variables in c++ in the most simple example, pretending I need to lock 2 variables in a function or a thread

You mean like this: http://en.cppreference.com/w/cpp/thread/lock_guard? — Mike Seymour, Nov 08 '14 at 11:46
example in cppreference is more than enough, it's quite simple. — oblitum, Nov 08 '14 at 11:48
@Arwa196 _"Can I lock a variable of type int ?"_ Did you actually read the sample there? — πάντα ῥεῖ, Nov 08 '14 at 11:51
No, you don't lock just any variable, the lock itself is a variable you use in order to ensure you have ownership of some critical section — Leeor, Nov 08 '14 at 11:51

score 4 · Accepted Answer · answered Nov 08 '14 at 11:49

4

Given:

int a;
int b;
std::mutex mutex;

Just do:

{
    std::lock_guard<decltype(mutex)> lock(mutex);
    ++a; // or whatever you wanna do to a
    b += a; // or whatever you wanna do to b
}

This will release the lock at the } automatically.

If you want to make sure that a lock is acquired before accessing the variables in question, you'll have to write a wrapper.

answered Nov 08 '14 at 11:49

this will lock a and b for the { } scope,Right ? what if I don't need to lock all the variables in that scope ? – Arwa196 Nov 08 '14 at 11:53
No, it locks `mutex`. If you want to be sure the mutex is locked when accessing `a` and `b`, you'll have to write a wrapper as I mentioned in the answer. – Nov 08 '14 at 11:54
You cannot lock arbitrary variables. You can only lock objects that have a `lock` method (see [`BasicLockable`](http://en.cppreference.com/w/cpp/concept/BasicLockable)). – Nov 08 '14 at 11:54

How to acquire a lock in C++?

1 Answers1