std::shared_lock<Mutex>::shared_lock
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< cpp | thread | shared lock
| shared_lock() noexcept; |
(1) | (since C++14) |
| shared_lock( shared_lock&& other ) noexcept; |
(2) | (since C++14) |
| explicit shared_lock( mutex_type& m ); |
(3) | (since C++14) |
| shared_lock( mutex_type& m, std::defer_lock_t t ) noexcept; |
(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, |
(7) | (since C++14) |
| template< class Clock, class Duration > shared_lock( mutex_type& m, |
(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().
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().
6) Assumes the calling thread already holds a shared lock (i.e., a lock acquired by
lock_shared, try_lock_shared, try_lock_shared_for, or try_lock_shared_until) on m. The behavior is undefined if not so.7) Tries to lock the associated mutex in shared mode by calling m.try_lock_shared_for(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
Mutex does not meet the SharedTimedLockable requirements.8) Tries to lock the associated mutex in shared mode by calling m.try_lock_shared_until(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
Mutex does not meet the SharedTimedLockable requirements.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 |
Example
Run this code
#include <chrono> #include <iostream> #include <shared_mutex> #include <syncstream> #include <thread> std::shared_timed_mutex m; int i = 10; void read_shared_var(int id) { // both the threads get access to the integer i std::shared_lock<std::shared_timed_mutex> slk(m); const int ii = i; // reads global i std::osyncstream(std::cout) << '#' << id << " read i as " << ii << "...\n"; std::this_thread::sleep_for(std::chrono::milliseconds(10)); std::osyncstream(std::cout) << '#' << id << " woke up..." << std::endl; } int main() { std::thread r1{read_shared_var, 1}; std::thread r2{read_shared_var, 2}; r1.join(); r2.join(); }
Possible output:
#2 read i as 10... #1 read i as 10... #2 woke up... #1 woke up...