.. SPDX-FileCopyrightText: 2021 Intel Corporation .. .. SPDX-License-Identifier: CC-BY-4.0

============= rw_mutex

[mutex.rw_mutex]

A rw_mutex is a class that models :doc:ReaderWriterMutex requirement <../named_requirements/mutexes/rw_mutex> using an adaptive approach, it guarantees that the thread that cannot acquire the lock spins before blocking. The rw_mutex class satisfies all of the shared mutex requirements described in the [thread.sharedmutex.requirements] section of the ISO C++ standard. The rw_mutex class is an unfair reader-writer lock with a writer preference.

.. code:: cpp

// Defined in header <oneapi/tbb/rw_mutex.h>

namespace oneapi {
    namespace tbb {
        class rw_mutex {
        public:
            rw_mutex() noexcept;
            ~rw_mutex();

            rw_mutex(const rw_mutex&) = delete;
            rw_mutex& operator=(const rw_mutex&) = delete;

            class scoped_lock;

            // exclusive ownership
            void lock();
            bool try_lock();
            void unlock();

            // shared ownership
            void lock_shared();
            bool try_lock_shared();
            void unlock_shared();

            static constexpr bool is_rw_mutex = true;
            static constexpr bool is_recursive_mutex = false;
            static constexpr bool is_fair_mutex = false;
        };
    }
}

Member classes

.. namespace:: oneapi::tbb::rw_mutex

.. cpp:class:: scoped_lock

The corresponding scoped-lock class. See :doc:`ReaderWriterMutex requirement <../named_requirements/mutexes/rw_mutex>`.

Member functions

.. cpp:function:: rw_mutex()

Constructs an unlocked ``rw_mutex``.

.. cpp:function:: ~rw_mutex()

Destroys an unlocked ``rw_mutex``.

.. cpp:function:: void lock()

Acquires a lock. It uses an adaptive logic for waiting, thus it is blocked after a certain time of busy waiting.

.. cpp:function:: bool try_lock()

Tries to acquire a lock (non-blocking) on write. Returns **true** if succeeded; **false** otherwise.

.. cpp:function:: void unlock()

Releases the write lock held by the current thread.

.. cpp:function:: void lock_shared()

Acquires a lock on read. It uses an adaptive logic for waiting, thus it is blocked after a certain time of busy waiting.

.. cpp:function:: bool try_lock_shared()

Tries to acquire the lock (non-blocking) on read. Returns **true** if succeeded; **false** otherwise.

.. cpp:function:: void unlock_shared()

Releases the read lock held by the current thread.