stdsharedlockstdsharedmutex

stdsharedlockstdsharedmutex refers to the two related components in the C++ standard library that provide shared (read) synchronization: std::shared_lock and std::shared_mutex. They are defined in the header <shared_mutex> and are part of C++17 and later, with earlier equivalents existing in the form of std::shared_timed_mutex in some implementations.

std::shared_mutex is a mutex type that allows multiple threads to hold a shared lock simultaneously (readers), while only one thread can hold an exclusive lock (writer) at a time. It supports operations such as lock(), unlock(), lock_shared(), unlock_shared(), and their try_lock variants. Shared locking enables concurrent reads of protected data, whereas writes are serialized to ensure data integrity. Because the same mutex can be locked in either shared or exclusive mode, careful design is required to avoid deadlocks and to manage lock lifetimes properly.

std::shared_lock is a RAII wrapper that acquires a shared lock on a std::shared_mutex. It is designed for read access and releases the lock upon destruction. A shared_lock is movable and can be used with defer_lock or adopt_lock to integrate with existing locking strategies. In practice, readers acquire a std::shared_lock<std::shared_mutex>, while writers typically use a std::unique_lock<std::shared_mutex> (or, in some cases, a std::lock_guard<std::shared_mutex>) to obtain exclusive access.

Usage patterns commonly arise in read-mostly data structures, where many threads perform reads concurrently and occasional writes require exclusive access. The shared_mutex-based approach can improve throughput in such scenarios compared to exclusive locking alone, but it introduces potential writer starvation and contention under high concurrency. Availability and behavior can vary by standard library implementation, and certain timed operations may require std::shared_timed_mutex in older standards.

See also: std::unique_lock, std::lock_guard, std::shared_timed_mutex.