what is the use of Csinglelock?

Question

It is mentioned in MSDN, that to lock and Unlock CCriticalSection object, we should use CSingleLock. But CCriticalSection::lock() and CCriticalSection::unlock() does the same thing, doesn't it? Then What is the difference between both the methods?

It's too large a subject for a simple answer, but you should learn about [exception safety](http://en.wikipedia.org/wiki/Exception_safety) and [RAII](http://stackoverflow.com/questions/2321511). What would happen if something threw an exception between `lock` and `unlock`? How is a destructor different from an explicit function call? — Mike Seymour, Feb 03 '15 at 07:28

score 1 · Accepted Answer · answered Feb 03 '15 at 08:07

Using a wrapper will ensure that (almost) no matter what you do from the point where you are locking the lock, when you leave the function, it will unlock.

Consider:

void func()
{
    lock();
    ... plenty of lines ... 
    // x = 8128 happens on a Wednesday, in a month without 
    // r in the name, only if the day is divisible by 7 and 3. 
    if (x == 8128)
       return;
    ... more lines of code ... 
    unlock();
}

So, once every now and again, your application forgets to unlock the lock.

The same applies if you get an exception, use goto, etc.

If you use a wrapper, you are guaranteed that the destructor will be called when the scope of the wrapper ends. This is just as useful for std::string or std::vector as it is for locks.

Of course, it won't help if you use for example longjmp to jump out of the context. But then you shouldn't be using longjmp!

what is the use of Csinglelock?

1 Answers1