33 Thread support library [thread]

33.4 Mutual exclusion [thread.mutex]

33.4.3 Mutex requirements [thread.mutex.requirements] Mutex types [thread.mutex.requirements.mutex] Class recursive_­mutex [thread.mutex.recursive]

namespace std {
  class recursive_mutex {

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

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

    using native_handle_type = implementation-defined; // 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 of the mutex requirements. It shall be a standard-layout 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: