找了好久的pthread_mutex_lock函数的实现原理，，现粘贴如下。。。
int
__pthread_mutex_lock (mutex)
pthread_mutex_t *mutex;
{
assert (sizeof (mutex->__size) >= sizeof (mutex->__data));
int oldval;
pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
int retval = 0;
switch (__builtin_expect (mutex->__data.__kind, PTHREAD_MUTEX_TIMED_NP))
{
/* Recursive mutex. */
case PTHREAD_MUTEX_RECURSIVE_NP:
/* Check whether we already hold the mutex. */
if (mutex->__data.__owner == id)
{
/* Just bump the counter. */
if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
/* Overflow of the counter. */
return EAGAIN;
++mutex->__data.__count;
return 0;
}
/* We have to get the mutex. */
LLL_MUTEX_LOCK (mutex->__data.__lock);
assert (mutex->__data.__owner == 0);
mutex->__data.__count = 1;
break;
/* Error checking mutex. */
case PTHREAD_MUTEX_ERRORCHECK_NP:
/* Check whether we already hold the mutex. */
if (__builtin_expect (mutex->__data.__owner == id, 0))
return EDEADLK;
/* FALLTHROUGH */
case PTHREAD_MUTEX_TIMED_NP:
simple:
/* Normal mutex. */
LLL_MUTEX_LOCK (mutex->__data.__lock);
assert (mutex->__data.__owner == 0);
break;
case PTHREAD_MUTEX_ADAPTIVE_NP:
if (! __is_smp)
goto simple;
if (LLL_MUTEX_TRYLOCK (mutex->__data.__lock) != 0)
{
int cnt = 0;
int max_cnt = MIN (MAX_ADAPTIVE_COUNT,
mutex->__data.__spins * 2 + 10);
do
{
if (cnt++ >= max_cnt)
{
LLL_MUTEX_LOCK (mutex->__data.__lock);
break;
}
#ifdef BUSY_WAIT_NOP
BUSY_WAIT_NOP;
#endif
}
while (LLL_MUTEX_TRYLOCK (mutex->__data.__lock) != 0);
mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8;
}
assert (mutex->__data.__owner == 0);
break;
case PTHREAD_MUTEX_ROBUST_RECURSIVE_NP:
case PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP:
case PTHREAD_MUTEX_ROBUST_NORMAL_NP:
case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
&mutex->__data.__list.__next);
oldval = mutex->__data.__lock;
do
{
again:
if ((oldval & FUTEX_OWNER_DIED) != 0)
{
/* The previous owner died. Try locking the mutex. */
int newval = id;
#ifdef NO_INCR
newval |= FUTEX_WAITERS;
#else
newval |= (oldval & FUTEX_WAITERS);
#endif
newval
= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
newval, oldval);
if (newval != oldval)
{
oldval = newval;
goto again;
}
/* We got the mutex. */
mutex->__data.__count = 1;
/* But it is inconsistent unless marked otherwise. */
mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
ENQUEUE_MUTEX (mutex);
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Note that we deliberately exit here. If we fall
through to the end of the function __nusers would be
incremented which is not correct because the old
owner has to be discounted. If we are not supposed
to increment __nusers we actually have to decrement
it here. */
#ifdef NO_INCR
--mutex->__data.__nusers;
#endif
return EOWNERDEAD;
}
/* Check whether we already hold the mutex. */
if (__builtin_expect ((oldval & FUTEX_TID_MASK) == id, 0))
{
if (mutex->__data.__kind
== PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
{
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
NULL);
return EDEADLK;
}
if (mutex->__data.__kind
== PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
{
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
NULL);
/* Just bump the counter. */
if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
/* Overflow of the counter. */
return EAGAIN;
++mutex->__data.__count;
return 0;
}
}
oldval = LLL_ROBUST_MUTEX_LOCK (mutex->__data.__lock, id);
if (__builtin_expect (mutex->__data.__owner
== PTHREAD_MUTEX_NOTRECOVERABLE, 0))
{
/* This mutex is now not recoverable. */
mutex->__data.__count = 0;
lll_mutex_unlock (mutex->__data.__lock);
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return ENOTRECOVERABLE;
}
}
while ((oldval & FUTEX_OWNER_DIED) != 0);
mutex->__data.__count = 1;
ENQUEUE_MUTEX (mutex);
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
break;
case PTHREAD_MUTEX_PI_RECURSIVE_NP:
case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
case PTHREAD_MUTEX_PI_NORMAL_NP:
case PTHREAD_MUTEX_PI_ADAPTIVE_NP:
case PTHREAD_MUTEX_PI_ROBUST_RECURSIVE_NP:
case PTHREAD_MUTEX_PI_ROBUST_ERRORCHECK_NP:
case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP:
case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP:
{
int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
if (robust)
/* Note: robust PI futexes are signaled by setting bit 0. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
(void *) (((uintptr_t) &mutex->__data.__list.__next)
| 1));
oldval = mutex->__data.__lock;
/* Check whether we already hold the mutex. */
if (__builtin_expect ((oldval & FUTEX_TID_MASK) == id, 0))
{
if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
{
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EDEADLK;
}
if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
{
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Just bump the counter. */
if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
/* Overflow of the counter. */
return EAGAIN;
++mutex->__data.__count;
return 0;
}
}
int newval = id;
#ifdef NO_INCR
newval |= FUTEX_WAITERS;
#endif
oldval = atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
newval, 0);
if (oldval != 0)
{
/* The mutex is locked. The kernel will now take care of
everything. */
INTERNAL_SYSCALL_DECL (__err);
int e = INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
FUTEX_LOCK_PI, 1, 0);
if (INTERNAL_SYSCALL_ERROR_P (e, __err)
&& (INTERNAL_SYSCALL_ERRNO (e, __err) == ESRCH
|| INTERNAL_SYSCALL_ERRNO (e, __err) == EDEADLK))
{
assert (INTERNAL_SYSCALL_ERRNO (e, __err) != EDEADLK
|| (kind != PTHREAD_MUTEX_ERRORCHECK_NP
&& kind != PTHREAD_MUTEX_RECURSIVE_NP));
/* ESRCH can happen only for non-robust PI mutexes where
the owner of the lock died. */
assert (INTERNAL_SYSCALL_ERRNO (e, __err) != ESRCH || !robust);
/* Delay the thread indefinitely. */
while (1)
pause_not_cancel ();
}
oldval = mutex->__data.__lock;
assert (robust || (oldval & FUTEX_OWNER_DIED) == 0);
}
if (__builtin_expect (oldval & FUTEX_OWNER_DIED, 0))
{
atomic_and (&mutex->__data.__lock, ~FUTEX_OWNER_DIED);
/* We got the mutex. */
mutex->__data.__count = 1;
/* But it is inconsistent unless marked otherwise. */
mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
ENQUEUE_MUTEX_PI (mutex);
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Note that we deliberately exit here. If we fall
through to the end of the function __nusers would be
incremented which is not correct because the old owner
has to be discounted. If we are not supposed to
increment __nusers we actually have to decrement it here. */
#ifdef NO_INCR
--mutex->__data.__nusers;
#endif
return EOWNERDEAD;
}
if (robust
&& __builtin_expect (mutex->__data.__owner
== PTHREAD_MUTEX_NOTRECOVERABLE, 0))
{
/* This mutex is now not recoverable. */
mutex->__data.__count = 0;
INTERNAL_SYSCALL_DECL (__err);
INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
FUTEX_UNLOCK_PI, 0, 0);
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return ENOTRECOVERABLE;
}
mutex->__data.__count = 1;
if (robust)
{
ENQUEUE_MUTEX_PI (mutex);
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
}
}
break;
case PTHREAD_MUTEX_PP_RECURSIVE_NP:
case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
case PTHREAD_MUTEX_PP_NORMAL_NP:
case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
{
int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
oldval = mutex->__data.__lock;
/* Check whether we already hold the mutex. */
if (mutex->__data.__owner == id)
{
if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
return EDEADLK;
if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
{
/* Just bump the counter. */
if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
/* Overflow of the counter. */
return EAGAIN;
++mutex->__data.__count;
return 0;
}
}
int oldprio = -1, ceilval;
do
{
int ceiling = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
>> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
if (__pthread_current_priority () > ceiling)
{
if (oldprio != -1)
__pthread_tpp_change_priority (oldprio, -1);
return EINVAL;
}
retval = __pthread_tpp_change_priority (oldprio, ceiling);
if (retval)
return retval;
ceilval = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
oldprio = ceiling;
oldval
= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
#ifdef NO_INCR
ceilval | 2,
#else
ceilval | 1,
#endif
ceilval);
if (oldval == ceilval)
break;
do
{
oldval
= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
ceilval | 2,
ceilval | 1);
if ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval)
break;
if (oldval != ceilval)
lll_futex_wait (&mutex->__data.__lock, ceilval | 2);
}
while (atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
ceilval | 2, ceilval)
!= ceilval);
}
while ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval);
assert (mutex->__data.__owner == 0);
mutex->__data.__count = 1;
}
break;
default:
/* Correct code cannot set any other type. */
return EINVAL;
}
/* Record the ownership. */
mutex->__data.__owner = id;
#ifndef NO_INCR
++mutex->__data.__nusers;
#endif
return retval;
}
#ifndef __pthread_mutex_lock
strong_alias (__pthread_mutex_lock, pthread_mutex_lock)
strong_alias (__pthread_mutex_lock, __pthread_mutex_lock_internal)
#endif