The analyzer has detected a problem. An object of the 'std::scoped_lock' type is constructed without arguments passed to it — i.e., without lockable objects. This can lead to problems in a multithreaded application: race condition, data race, etc.
Since C++17, the standard library has 'std::scoped_lock' class template. It was implemented as a convenient alternative to 'std::lock_guard'. We can use 'std::scoped_lock' when we need to lock an arbitrary number of lockable objects at a time. The class provides an algorithm that prevents deadlocks.
However, the new design has certain disadvantages. Let's see how we can declare one of its constructors:
template <class ...MutexTypes>
class scoped_lock
{
// ....
public:
explicit scoped_lock(MutexTypes &...m);
// ....
};The constructor receives an arbitrary number of arguments of the 'MutexTypes' (parameter pack) type. The parameter pack 'MutexTypes' can be empty. As a result, we can get a RAII object without locks:
void bad()
{
// ....
std::scoped_lock lock;
// ....
}To fix this, we should initialize 'std::scoped_lock' with a lockable object:
std::mutex mtx;
void good()
{
// ....
std::scoped_lock lock { mtx };
// ....
}This diagnostic is classified as:
|