std::shared_lock::shared_lock

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std::shared_lock
 
shared_lock();
 (1) (since C++14)
shared_lock( shared_lock&& other );
 (2) (since C++14)
explicit shared_lock( mutex_type& m );
 (3) (since C++14)
shared_lock( mutex_type& m, std::defer_lock_t t );
 (4) (since C++14)
shared_lock( mutex_type& m, std::try_to_lock_t t );
 (5) (since C++14)
shared_lock( mutex_type& m, std::adopt_lock_t t );
 (6) (since C++14)
template< class Rep, class Period >

shared_lock( mutex_type& m,

             const std::chrono::duration<Rep,Period>& timeout_duration );
 (7) (since C++14)
template< class Clock, class Duration >

shared_lock( mutex_type& m,

             const std::chrono::time_point<Clock,Duration>& timeout_time );
 (8) (since C++14)

Constructs a shared_lock, optionally locking the supplied mutex.

1) Constructs a shared_lock with no associated mutex.
2) Move constructor. Initializes the shared_lock with the contents of other. Leaves other with no associated mutex.
3-8) Constructs a shared_lock with m as the associated mutex. Additionally:
3) Locks the associated mutex in shared mode by calling m.lock_shared(). The behavior is undefined if this thread already owns the mutex in any mode.
4) Does not lock the associated mutex.
5) Tries to lock the associated mutex in shared mode without blocking by calling m.try_lock_shared(). The behavior is undefined if this thread already owns the mutex in any mode.
6) Assumes the calling thread already owns m in shared mode.
7) Tries to lock the associated mutex in shared mode by calling m.try_lock_shared_until(timeout_duration), which blocks until specified timeout_duration has elapsed or the lock is acquired, whichever comes first. May block for longer than timeout_duration. The behavior is undefined if this thread already owns the mutex in any mode.
8) Tries to lock the associated mutex in shared mode by calling m.try_lock_shared_for(timeout_time), which 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. The behavior is undefined if this thread already owns the mutex in any mode.

Parameters

other - another shared_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

1,2,4)
noexcept specification:  
noexcept
  

Example

Run this code
#include <shared_mutex>
#include <iostream>
#include <thread>
#include <chrono>
 
std::shared_timed_mutex m;
int i = 10;
 
void read()
{
   // both the threads get access to the integer i
   std::shared_lock<std::shared_timed_mutex> slk(m);
   std::cout << "read i as " << i << "...\n"; // this is not synchronized
   std::this_thread::sleep_for(std::chrono::milliseconds(10));
   std::cout << "woke up...\n";
}
 
int main()
{
   std::thread r1(read);
   std::thread r2(read);
 
   r1.join();
   r2.join();
   return 0;
}


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