std::unique_lock::unique_lock

unique_lock() noexcept;	(1)	(since C++11)
unique_lock( unique_lock&& other ) noexcept;	(2)	(since C++11)
explicit unique_lock( mutex_type& m );	(3)	(since C++11)
unique_lock( mutex_type& m, std::defer_lock_t t ) noexcept;	(4)	(since C++11)
unique_lock( mutex_type& m, std::try_to_lock_t t );	(5)	(since C++11)
unique_lock( mutex_type& m, std::adopt_lock_t t );	(6)	(since C++11)
template< class Rep, class Period > unique_lock( mutex_type& m, const std::chrono::duration<Rep,Period>& timeout_duration );	(7)	(since C++11)
template< class Clock, class Duration > unique_lock( mutex_type& m, const std::chrono::time_point<Clock,Duration>& timeout_time );	(8)	(since C++11)

Constructs a unique_lock, optionally locking the supplied mutex.

1) Constructs a unique_lock with no associated mutex.

2) Move constructor. Initializes the unique_lock with the contents of other. Leaves other with no associated mutex.

3-8) Constructs a unique_lock with m as the associated mutex. Additionally:

3) Locks the associated mutex by calling m.lock(). The behavior is undefined if the current thread already owns the mutex except when the mutex is recursive.

4) Does not lock the associated mutex.

5) Tries to lock the associated mutex without blocking by calling m.try_lock(). The behavior is undefined if the current thread already owns the mutex except when the mutex is recursive.

6) Assumes the calling thread already owns m.

7) Tries to lock the associated mutex by calling m.try_lock_for(timeout_duration). Blocks until specified timeout_duration has elapsed or the lock is acquired, whichever comes first. May block for longer than timeout_duration.

8) Tries to lock the associated mutex by calling m.try_lock_until(timeout_time). Blocks until specified timeout_time has been reached or the lock is acquired, whichever comes first. May block for longer than until timeout_time has been reached.

Parameters

other	-	another `unique_lock` to initialize the state with
m	-	mutex to associate with the lock and optionally acquire ownership of
t	-	tag parameter used to select constructors with different locking strategies
timeout_duration	-	maximum duration to block for
timeout_time	-	maximum time point to block until

Exceptions

Example

Run this code

#include <iostream>
#include <thread>
#include <vector>
#include <mutex>
std::mutex m_a, m_b, m_c;
int a, b, c = 1;
void update()
{
    {   // Note: std::lock_guard or atomic<int> can be used instead
        std::unique_lock<std::mutex> lk(m_a);
        a++;
    }

    { // Note: see std::lock and std::scoped_lock for details and alternatives
      std::unique_lock<std::mutex> lk_b(m_b, std::defer_lock);
      std::unique_lock<std::mutex> lk_c(m_c, std::defer_lock);
      std::lock(lk_b, lk_c);
      b = std::exchange(c, b+c);
   }
}

int main()
{
  std::vector<std::thread> threads;
  for (unsigned i = 0; i < 12; ++i)
    threads.emplace_back(update);

  for (auto& i: threads)
    i.join();

  std::cout << a << "'th and " << a+1 << "'th Fibonacci numbers: "
            << b << " and " << c << '\n';
}

Output:

12'th and 13'th Fibonacci numbers: 144 and 233

Language
Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

Member functions
unique_lock::unique_lock
unique_lock::~unique_lock
unique_lock::operator=
Locking
unique_lock::lock
unique_lock::try_lock
unique_lock::try_lock_for
unique_lock::try_lock_until
unique_lock::unlock
Modifiers
unique_lock::swap
unique_lock::release
Observers
unique_lock::mutex
unique_lock::owns_lock
unique_lock::operator bool
Non-member functions
std::swap