32 Thread support library [thread]

32.5 Mutual exclusion [thread.mutex]

32.5.3 Mutex requirements [thread.mutex.requirements]

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

32.5.3.2.1 Class mutex [thread.mutex.class]

namespace std {
  class mutex {
  public:
    constexpr mutex() noexcept;
    ~mutex();

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

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

    using native_handle_type = implementation-defined;          // see [thread.req.native]
    native_handle_type native_handle();                         // see [thread.req.native]
  };
}
1
#
The class mutex provides a non-recursive mutex with exclusive ownership semantics.
If one thread owns a mutex object, attempts by another thread to acquire ownership of that object will fail (for try_­lock()) or block (for lock()) until the owning thread has released ownership with a call to unlock().
2
#
[ Note
:
After a thread A has called unlock(), releasing a mutex, it is possible for another thread B to lock the same mutex, observe that it is no longer in use, unlock it, and destroy it, before thread A appears to have returned from its unlock call.
Implementations are required to handle such scenarios correctly, as long as thread A doesn't access the mutex after the unlock call returns.
These cases typically occur when a reference-counted object contains a mutex that is used to protect the reference count.
— end note
 ]
3
#
The class mutex meets all of the mutex requirements ([thread.mutex.requirements]).
It is a standard-layout class ([class.prop]).
4
#
[ Note
:
A program can deadlock if the thread that owns a mutex object calls lock() on that object.
If the implementation can detect the deadlock, a resource_­deadlock_­would_­occur error condition might be observed.
— end note
 ]
5
#
The behavior of a program is undefined if it destroys a mutex object owned by any thread or a thread terminates while owning a mutex object.