How to put mutex lock & unlock for a specific condition in if-else ladder?

Question

In a member function of a class running in a thread I want to protect access to some shared resources in an if-else ladder like following.

if (condition)
{}
// the mutex lock should be here
else if (specific condition)
// the mutex unlock should be here
{}
else ...

I wish to do locking in above manner because apart from accessing the shared resource for evaluating the specific condition I do not access/use it anywhere and all the operations running every if/else block are pretty long running for which I do not want to block other thread from accessing that shared resource.

I am aware of scoped locks and mutexes but I cannot think of a way it can be used in this situation. Question is:

With mutex lock/unlock statement or even with a scoped lock how to achieve a lock/unlock on a specific condition in an if-else ladder?

Also I am looking to find this solution from C++ (03 perhaps) perspective (or for that matter not from languages like Java with implicit mutex support and synchronized blocks). Thanks in advance for all the help.

Answer 1

Wrap up the condition in a function that does the locking:

bool condition() {
    mutex_lock();
    bool result = ...
    mutex_unlock();
    return result;
}

then in the code just use

if () {
...
} else if (condition(...)) {
...
}

Answer 2

It should be work.

if (std::lock_guard{mutex_}, condition) {
...
}