结论：

最终std::mutex 会调用pthread_mutex_t 相关接口

1 std::mutex 定义封装关键数据：typedef __gthread_mutex_t

#ifdef _GLIBCXX_HAS_GTHREADS// Common base class for std::mutex and std::timed_mutexclass __mutex_base{protected:typedef __gthread_mutex_t            __native_type;#ifdef __GTHREAD_MUTEX_INIT__native_type  _M_mutex = __GTHREAD_MUTEX_INIT;constexpr __mutex_base() noexcept = default;
#else__native_type  _M_mutex;__mutex_base() noexcept{// XXX EAGAIN, ENOMEM, EPERM, EBUSY(may), EINVAL(may)__GTHREAD_MUTEX_INIT_FUNCTION(&_M_mutex);}~__mutex_base() noexcept { __gthread_mutex_destroy(&_M_mutex); }
#endif__mutex_base(const __mutex_base&) = delete;__mutex_base& operator=(const __mutex_base&) = delete;};/// The standard mutex type.class mutex : private __mutex_base{public:typedef __native_type*             native_handle_type;#ifdef __GTHREAD_MUTEX_INITconstexpr
#endifmutex() noexcept = default;~mutex() = default;mutex(const mutex&) = delete;mutex& operator=(const mutex&) = delete;voidlock(){int __e = __gthread_mutex_lock(&_M_mutex);// EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)if (__e)__throw_system_error(__e);}booltry_lock() noexcept{// XXX EINVAL, EAGAIN, EBUSYreturn !__gthread_mutex_trylock(&_M_mutex);}voidunlock(){// XXX EINVAL, EAGAIN, EPERM__gthread_mutex_unlock(&_M_mutex);}native_handle_typenative_handle() noexcept{ return &_M_mutex; }};#endif // _GLIBCXX_HAS_GTHREADS

typedef pthread_t __gthread_t;
typedef pthread_key_t __gthread_key_t;
typedef pthread_once_t __gthread_once_t;
typedef pthread_mutex_t __gthread_mutex_t;
typedef pthread_mutex_t __gthread_recursive_mutex_t;
typedef pthread_cond_t __gthread_cond_t;
typedef struct timespec __gthread_time_t;

typedef union
{struct __pthread_mutex_s __data;char __size[__SIZEOF_PTHREAD_MUTEX_T];long int __align;
} pthread_mutex_t;

struct __pthread_mutex_s
{int __lock;unsigned int __count;int __owner;
#ifdef __x86_64__unsigned int __nusers;
#endif/* KIND must stay at this position in the structure to maintainbinary compatibility with static initializers.  */int __kind;
#ifdef __x86_64__short __spins;short __elision;__pthread_list_t __list;
# define __PTHREAD_MUTEX_HAVE_PREV      1
#elseunsigned int __nusers;__extension__ union{struct{short __espins;short __eelision;
# define __spins __elision_data.__espins
# define __elision __elision_data.__eelision} __elision_data;__pthread_slist_t __list;};
# define __PTHREAD_MUTEX_HAVE_PREV      0
#endif
};

#  define __SIZEOF_PTHREAD_MUTEX_T 40

编译时候必须指定链接库：-lpthread

caros@caros-Alienware-m15-R6:~/study/C++_std/thread$ g++ mutex.cpp  
/usr/bin/ld: /tmp/ccZoZxMe.o: in function `std::thread::thread<void (&)(int), int, void>(void (&)(int), int&&)':
mutex.cpp:(.text._ZNSt6threadC2IRFviEJiEvEEOT_DpOT0_[_ZNSt6threadC5IRFviEJiEvEEOT_DpOT0_]+0x37): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
caros@caros-Alienware-m15-R6:~/study/C++_std/thread$ g++ mutex.cpp  -lpthread

参考文档：

https://cplusplus.com/reference/mutex/mutex/lock/