30 Thread support library [thread]

30.4 Mutual exclusion [thread.mutex]

30.4.1 Mutex requirements [thread.mutex.requirements]

30.4.1.2 Mutex types [thread.mutex.requirements.mutex]

30.4.1.2.2 Class recursive_mutex [thread.mutex.recursive]

namespace std {
  class recursive_mutex {
  public:
    recursive_mutex();
    ~recursive_mutex();

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

    void lock();
    bool try_lock() noexcept;
    void unlock();

    typedef implementation-defined native_handle_type; // See [thread.req.native]
    native_handle_type native_handle();                // See [thread.req.native]
  };
}

The class recursive_mutex provides a recursive mutex with exclusive ownership semantics. If one thread owns a recursive_mutex object, attempts by another thread to acquire ownership of that object will fail (for try_lock()) or block (for lock()) until the first thread has completely released ownership.

The class recursive_mutex shall satisfy all the Mutex requirements ([thread.mutex.requirements]). It shall be a standard-layout class (Clause [class]).

A thread that owns a recursive_mutex object may acquire additional levels of ownership by calling lock() or try_lock() on that object. It is unspecified how many levels of ownership may be acquired by a single thread. If a thread has already acquired the maximum level of ownership for a recursive_mutex object, additional calls to try_lock() shall fail, and additional calls to lock() shall throw an exception of type system_error. A thread shall call unlock() once for each level of ownership acquired by calls to lock() and try_lock(). Only when all levels of ownership have been released may ownership be acquired by another thread.

The behavior of a program is undefined if:

  • it destroys a recursive_mutex object owned by any thread or

  • a thread terminates while owning a recursive_mutex object.