std::scoped_lock

 

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std::scoped_lock

Member functions

scoped_lock::scoped_lock

scoped_lock::~scoped_lock

 

Defined in header <mutex>
template< class... MutexTypes > class scoped_lock;		(since C++17)

The class scoped_lock is a mutex wrapper that provides a convenient RAII-style mechanism for owning one or more mutexes for the duration of a scoped block.

When a scoped_lock object is created, it attempts to take ownership of the mutexes it is given. When control leaves the scope in which the scoped_lock object was created, the scoped_lock is destructed and the mutexes are released, in reverse order. If several mutexes are given, deadlock avoidance algorithm is used as if by std::lock.

The scoped_lock class is non-copyable.

Template parameters

MutexTypes

-

the types of the mutexes to lock. The types must meet the Lockable requirements unless sizeof...(MutexTypes)==1, in which case the only type must meet BasicLockable

Member types

Member type	Definition
mutex_type	Mutex

Member functions

(constructor)	constructs a scoped_lock, optionally locking the given mutexes (public member function)
(destructor)	destructs the scoped_lock object, unlocks the underlying mutexes (public member function)
operator= [deleted]	not copy-assignable (public member function)

Example

Run this code

#include <thread>
#include <mutex>
#include <iostream>
 
int g_i = 0;
std::mutex g_i_mutex;  // protects g_i
 
void safe_increment()
{
    std::scoped_lock lock{g_i_mutex};
    ++g_i;
 
    std::cout << std::this_thread::get_id() << ": " << g_i << '\n';
 
    // g_i_mutex is automatically released when lock
    // goes out of scope
}
 
int main()
{
    std::cout << __func__ << ": " << g_i << '\n';
 
    std::thread t1(safe_increment);
    std::thread t2(safe_increment);
 
    t1.join();
    t2.join();
 
    std::cout << __func__ << ": " << g_i << '\n';
}

Possible output:

main: 0
140641306900224: 1
140641298507520: 2
main: 2

See also

unique_lock (C++11)

implements movable mutex ownership wrapper (class template)

lock_guard (C++11)

implements a strictly scope-based mutex ownership wrapper (class template)