Why is STD mutex not movable?

By design, std::mutex is not movable nor copyable. This means that a class A holding a mutex won’t receive a default move constructor.

Can mutex be copied?

In addition to the answer below, mutex handles cannot be copied at the OS level either. In Windows, you have to create a named mutex and then open a new handle based on that name, for example, intended to be used in a new thread/process and std::mutex never creates named objects.

What is the difference between copy constructor and move constructor?

Move constructor moves the resources in the heap, i.e., unlike copy constructors which copy the data of the existing object and assigning it to the new object move constructor just makes the pointer of the declared object to point to the data of temporary object and nulls out the pointer of the temporary objects.

What happens when mutex is locked?

Mutexes are used to protect shared resources. If the mutex is already locked by another thread, the thread waits for the mutex to become available. The thread that has locked a mutex becomes its current owner and remains the owner until the same thread has unlocked it.

What is STD mutex?

std::mutex The mutex class is a synchronization primitive that can be used to protect shared data from being simultaneously accessed by multiple threads. A calling thread owns a mutex from the time that it successfully calls either lock or try_lock until it calls unlock .

Why is mutex mutable?

The point is that, even in a const object, the mutex must be able to be locked/unlocked. So even in a const object, the mutex must be non-const. Hence, it must be declared mutable.

What does std :: move do?

std::move is used to indicate that an object t may be “moved from”, i.e. allowing the efficient transfer of resources from t to another object. In particular, std::move produces an xvalue expression that identifies its argument t . It is exactly equivalent to a static_cast to an rvalue reference type.

Can another thread unlock mutex?

If a thread attempts to unlock a mutex that it has not locked or a mutex which is unlocked, undefined behavior results. As user562734’s answer says, the answer is no – you cannot unlock a thread that was locked by another thread.

Is mutex movable or copyable?

By design, std::mutex is not movable nor copyable. This means that a class A holding a mutex won’t receive a default move constructor. How would I make this type A movable in a thread-safe way?

What is mutex in stdstd?

std::mutex The mutex class is a synchronization primitive that can be used to protect shared data from being simultaneously accessed by multiple threads. mutex offers exclusive, non-recursive ownership semantics: A calling thread owns a mutex from the time that it successfully calls either lock or try_lock until it calls unlock.

What happens when a mutex is destroyed?

The behavior of a program is undefined if a mutex is destroyed while still owned by any threads, or a thread terminates while owning a mutex. The mutex class satisfies all requirements of Mutex and StandardLayoutType. std::mutex is neither copyable nor movable.

What happens when a thread acquires a mutex in Java?

If a thread acquires a mutex, the second thread that wants to acquire that mutex is suspended until the first thread releases the mutex. This type implements the IDisposable interface. When you have finished using the type, you should dispose of it either directly or indirectly.