glibc/nptl/pthread_mutex_lock.c
Wangyang Guo 8162147872 nptl: Add backoff mechanism to spinlock loop
When mutiple threads waiting for lock at the same time, once lock owner
releases the lock, waiters will see lock available and all try to lock,
which may cause an expensive CAS storm.

Binary exponential backoff with random jitter is introduced. As try-lock
attempt increases, there is more likely that a larger number threads
compete for adaptive mutex lock, so increase wait time in exponential.
A random jitter is also added to avoid synchronous try-lock from other
threads.

v2: Remove read-check before try-lock for performance.

v3:
1. Restore read-check since it works well in some platform.
2. Make backoff arch dependent, and enable it for x86_64.
3. Limit max backoff to reduce latency in large critical section.

v4: Fix strict-prototypes error in sysdeps/nptl/pthread_mutex_backoff.h

v5: Commit log updated for regression in large critical section.

Result of pthread-mutex-locks bench

Test Platform: Xeon 8280L (2 socket, 112 CPUs in total)
First Row: thread number
First Col: critical section length
Values: backoff vs upstream, time based, low is better

non-critical-length: 1
	1	2	4	8	16	32	64	112	140
0	0.99	0.58	0.52	0.49	0.43	0.44	0.46	0.52	0.54
1	0.98	0.43	0.56	0.50	0.44	0.45	0.50	0.56	0.57
2	0.99	0.41	0.57	0.51	0.45	0.47	0.48	0.60	0.61
4	0.99	0.45	0.59	0.53	0.48	0.49	0.52	0.64	0.65
8	1.00	0.66	0.71	0.63	0.56	0.59	0.66	0.72	0.71
16	0.97	0.78	0.91	0.73	0.67	0.70	0.79	0.80	0.80
32	0.95	1.17	0.98	0.87	0.82	0.86	0.89	0.90	0.90
64	0.96	0.95	1.01	1.01	0.98	1.00	1.03	0.99	0.99
128	0.99	1.01	1.01	1.17	1.08	1.12	1.02	0.97	1.02

non-critical-length: 32
	1	2	4	8	16	32	64	112	140
0	1.03	0.97	0.75	0.65	0.58	0.58	0.56	0.70	0.70
1	0.94	0.95	0.76	0.65	0.58	0.58	0.61	0.71	0.72
2	0.97	0.96	0.77	0.66	0.58	0.59	0.62	0.74	0.74
4	0.99	0.96	0.78	0.66	0.60	0.61	0.66	0.76	0.77
8	0.99	0.99	0.84	0.70	0.64	0.66	0.71	0.80	0.80
16	0.98	0.97	0.95	0.76	0.70	0.73	0.81	0.85	0.84
32	1.04	1.12	1.04	0.89	0.82	0.86	0.93	0.91	0.91
64	0.99	1.15	1.07	1.00	0.99	1.01	1.05	0.99	0.99
128	1.00	1.21	1.20	1.22	1.25	1.31	1.12	1.10	0.99

non-critical-length: 128
	1	2	4	8	16	32	64	112	140
0	1.02	1.00	0.99	0.67	0.61	0.61	0.61	0.74	0.73
1	0.95	0.99	1.00	0.68	0.61	0.60	0.60	0.74	0.74
2	1.00	1.04	1.00	0.68	0.59	0.61	0.65	0.76	0.76
4	1.00	0.96	0.98	0.70	0.63	0.63	0.67	0.78	0.77
8	1.01	1.02	0.89	0.73	0.65	0.67	0.71	0.81	0.80
16	0.99	0.96	0.96	0.79	0.71	0.73	0.80	0.84	0.84
32	0.99	0.95	1.05	0.89	0.84	0.85	0.94	0.92	0.91
64	1.00	0.99	1.16	1.04	1.00	1.02	1.06	0.99	0.99
128	1.00	1.06	0.98	1.14	1.39	1.26	1.08	1.02	0.98

There is regression in large critical section. But adaptive mutex is
aimed for "quick" locks. Small critical section is more common when
users choose to use adaptive pthread_mutex.

Signed-off-by: Wangyang Guo <wangyang.guo@intel.com>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
2022-05-09 14:38:40 -07:00

662 lines
20 KiB
C

/* Copyright (C) 2002-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <assert.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/param.h>
#include <not-cancel.h>
#include "pthreadP.h"
#include <atomic.h>
#include <futex-internal.h>
#include <stap-probe.h>
#include <shlib-compat.h>
/* Some of the following definitions differ when pthread_mutex_cond_lock.c
includes this file. */
#ifndef LLL_MUTEX_LOCK
/* lll_lock with single-thread optimization. */
static inline void
lll_mutex_lock_optimized (pthread_mutex_t *mutex)
{
/* The single-threaded optimization is only valid for private
mutexes. For process-shared mutexes, the mutex could be in a
shared mapping, so synchronization with another process is needed
even without any threads. If the lock is already marked as
acquired, POSIX requires that pthread_mutex_lock deadlocks for
normal mutexes, so skip the optimization in that case as
well. */
int private = PTHREAD_MUTEX_PSHARED (mutex);
if (private == LLL_PRIVATE && SINGLE_THREAD_P && mutex->__data.__lock == 0)
mutex->__data.__lock = 1;
else
lll_lock (mutex->__data.__lock, private);
}
# define LLL_MUTEX_LOCK(mutex) \
lll_lock ((mutex)->__data.__lock, PTHREAD_MUTEX_PSHARED (mutex))
# define LLL_MUTEX_LOCK_OPTIMIZED(mutex) lll_mutex_lock_optimized (mutex)
# define LLL_MUTEX_TRYLOCK(mutex) \
lll_trylock ((mutex)->__data.__lock)
# define LLL_ROBUST_MUTEX_LOCK_MODIFIER 0
# define LLL_MUTEX_LOCK_ELISION(mutex) \
lll_lock_elision ((mutex)->__data.__lock, (mutex)->__data.__elision, \
PTHREAD_MUTEX_PSHARED (mutex))
# define LLL_MUTEX_TRYLOCK_ELISION(mutex) \
lll_trylock_elision((mutex)->__data.__lock, (mutex)->__data.__elision, \
PTHREAD_MUTEX_PSHARED (mutex))
# define PTHREAD_MUTEX_LOCK ___pthread_mutex_lock
# define PTHREAD_MUTEX_VERSIONS 1
#endif
#ifndef LLL_MUTEX_READ_LOCK
# define LLL_MUTEX_READ_LOCK(mutex) \
atomic_load_relaxed (&(mutex)->__data.__lock)
#endif
static int __pthread_mutex_lock_full (pthread_mutex_t *mutex)
__attribute_noinline__;
int
PTHREAD_MUTEX_LOCK (pthread_mutex_t *mutex)
{
/* See concurrency notes regarding mutex type which is loaded from __kind
in struct __pthread_mutex_s in sysdeps/nptl/bits/thread-shared-types.h. */
unsigned int type = PTHREAD_MUTEX_TYPE_ELISION (mutex);
LIBC_PROBE (mutex_entry, 1, mutex);
if (__builtin_expect (type & ~(PTHREAD_MUTEX_KIND_MASK_NP
| PTHREAD_MUTEX_ELISION_FLAGS_NP), 0))
return __pthread_mutex_lock_full (mutex);
if (__glibc_likely (type == PTHREAD_MUTEX_TIMED_NP))
{
FORCE_ELISION (mutex, goto elision);
simple:
/* Normal mutex. */
LLL_MUTEX_LOCK_OPTIMIZED (mutex);
assert (mutex->__data.__owner == 0);
}
#if ENABLE_ELISION_SUPPORT
else if (__glibc_likely (type == PTHREAD_MUTEX_TIMED_ELISION_NP))
{
elision: __attribute__((unused))
/* This case can never happen on a system without elision,
as the mutex type initialization functions will not
allow to set the elision flags. */
/* Don't record owner or users for elision case. This is a
tail call. */
return LLL_MUTEX_LOCK_ELISION (mutex);
}
#endif
else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)
== PTHREAD_MUTEX_RECURSIVE_NP, 1))
{
/* Recursive mutex. */
pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
/* Check whether we already hold the mutex. */
if (mutex->__data.__owner == id)
{
/* Just bump the counter. */
if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
/* Overflow of the counter. */
return EAGAIN;
++mutex->__data.__count;
return 0;
}
/* We have to get the mutex. */
LLL_MUTEX_LOCK_OPTIMIZED (mutex);
assert (mutex->__data.__owner == 0);
mutex->__data.__count = 1;
}
else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)
== PTHREAD_MUTEX_ADAPTIVE_NP, 1))
{
if (LLL_MUTEX_TRYLOCK (mutex) != 0)
{
int cnt = 0;
int max_cnt = MIN (max_adaptive_count (),
mutex->__data.__spins * 2 + 10);
int spin_count, exp_backoff = 1;
unsigned int jitter = get_jitter ();
do
{
/* In each loop, spin count is exponential backoff plus
random jitter, random range is [0, exp_backoff-1]. */
spin_count = exp_backoff + (jitter & (exp_backoff - 1));
cnt += spin_count;
if (cnt >= max_cnt)
{
/* If cnt exceeds max spin count, just go to wait
queue. */
LLL_MUTEX_LOCK (mutex);
break;
}
do
atomic_spin_nop ();
while (--spin_count > 0);
/* Prepare for next loop. */
exp_backoff = get_next_backoff (exp_backoff);
}
while (LLL_MUTEX_READ_LOCK (mutex) != 0
|| LLL_MUTEX_TRYLOCK (mutex) != 0);
mutex->__data.__spins += (cnt - mutex->__data.__spins) / 8;
}
assert (mutex->__data.__owner == 0);
}
else
{
pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
assert (PTHREAD_MUTEX_TYPE (mutex) == PTHREAD_MUTEX_ERRORCHECK_NP);
/* Check whether we already hold the mutex. */
if (__glibc_unlikely (mutex->__data.__owner == id))
return EDEADLK;
goto simple;
}
pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
/* Record the ownership. */
mutex->__data.__owner = id;
#ifndef NO_INCR
++mutex->__data.__nusers;
#endif
LIBC_PROBE (mutex_acquired, 1, mutex);
return 0;
}
static int
__pthread_mutex_lock_full (pthread_mutex_t *mutex)
{
int oldval;
pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
switch (PTHREAD_MUTEX_TYPE (mutex))
{
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);
/* We need to set op_pending before starting the operation. Also
see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
oldval = mutex->__data.__lock;
/* This is set to FUTEX_WAITERS iff we might have shared the
FUTEX_WAITERS flag with other threads, and therefore need to keep it
set to avoid lost wake-ups. We have the same requirement in the
simple mutex algorithm.
We start with value zero for a normal mutex, and FUTEX_WAITERS if we
are building the special case mutexes for use from within condition
variables. */
unsigned int assume_other_futex_waiters = LLL_ROBUST_MUTEX_LOCK_MODIFIER;
while (1)
{
/* Try to acquire the lock through a CAS from 0 (not acquired) to
our TID | assume_other_futex_waiters. */
if (__glibc_likely (oldval == 0))
{
oldval
= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
id | assume_other_futex_waiters, 0);
if (__glibc_likely (oldval == 0))
break;
}
if ((oldval & FUTEX_OWNER_DIED) != 0)
{
/* The previous owner died. Try locking the mutex. */
int newval = id;
#ifdef NO_INCR
/* We are not taking assume_other_futex_waiters into accoount
here simply because we'll set FUTEX_WAITERS anyway. */
newval |= FUTEX_WAITERS;
#else
newval |= (oldval & FUTEX_WAITERS) | assume_other_futex_waiters;
#endif
newval
= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
newval, oldval);
if (newval != oldval)
{
oldval = newval;
continue;
}
/* We got the mutex. */
mutex->__data.__count = 1;
/* But it is inconsistent unless marked otherwise. */
mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
/* We must not enqueue the mutex before we have acquired it.
Also see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
ENQUEUE_MUTEX (mutex);
/* We need to clear op_pending after we enqueue the mutex. */
__asm ("" ::: "memory");
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 (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
{
int kind = PTHREAD_MUTEX_TYPE (mutex);
if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
{
/* We do not need to ensure ordering wrt another memory
access. Also see comments at ENQUEUE_MUTEX. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
NULL);
return EDEADLK;
}
if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
{
/* We do not need to ensure ordering wrt another memory
access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
NULL);
/* Just bump the counter. */
if (__glibc_unlikely (mutex->__data.__count + 1 == 0))
/* Overflow of the counter. */
return EAGAIN;
++mutex->__data.__count;
return 0;
}
}
/* We cannot acquire the mutex nor has its owner died. Thus, try
to block using futexes. Set FUTEX_WAITERS if necessary so that
other threads are aware that there are potentially threads
blocked on the futex. Restart if oldval changed in the
meantime. */
if ((oldval & FUTEX_WAITERS) == 0)
{
int val = atomic_compare_and_exchange_val_acq
(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
if (val != oldval)
{
oldval = val;
continue;
}
oldval |= FUTEX_WAITERS;
}
/* It is now possible that we share the FUTEX_WAITERS flag with
another thread; therefore, update assume_other_futex_waiters so
that we do not forget about this when handling other cases
above and thus do not cause lost wake-ups. */
assume_other_futex_waiters |= FUTEX_WAITERS;
/* Block using the futex and reload current lock value. */
futex_wait ((unsigned int *) &mutex->__data.__lock, oldval,
PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
oldval = mutex->__data.__lock;
}
/* We have acquired the mutex; check if it is still consistent. */
if (__builtin_expect (mutex->__data.__owner
== PTHREAD_MUTEX_NOTRECOVERABLE, 0))
{
/* This mutex is now not recoverable. */
mutex->__data.__count = 0;
int private = PTHREAD_ROBUST_MUTEX_PSHARED (mutex);
lll_unlock (mutex->__data.__lock, private);
/* FIXME This violates the mutex destruction requirements. See
__pthread_mutex_unlock_full. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return ENOTRECOVERABLE;
}
mutex->__data.__count = 1;
/* We must not enqueue the mutex before we have acquired it.
Also see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
ENQUEUE_MUTEX (mutex);
/* We need to clear op_pending after we enqueue the mutex. */
__asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
break;
/* The PI support requires the Linux futex system call. If that's not
available, pthread_mutex_init should never have allowed the type to
be set. So it will get the default case for an invalid type. */
#ifdef __NR_futex
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, robust;
{
/* See concurrency notes regarding __kind in struct __pthread_mutex_s
in sysdeps/nptl/bits/thread-shared-types.h. */
int mutex_kind = atomic_load_relaxed (&(mutex->__data.__kind));
kind = mutex_kind & PTHREAD_MUTEX_KIND_MASK_NP;
robust = mutex_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));
/* We need to set op_pending before starting the operation. Also
see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
}
oldval = mutex->__data.__lock;
/* Check whether we already hold the mutex. */
if (__glibc_unlikely ((oldval & FUTEX_TID_MASK) == id))
{
if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
{
/* We do not need to ensure ordering wrt another memory
access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return EDEADLK;
}
if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
{
/* We do not need to ensure ordering wrt another memory
access. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
/* Just bump the counter. */
if (__glibc_unlikely (mutex->__data.__count + 1 == 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. */
int private = (robust
? PTHREAD_ROBUST_MUTEX_PSHARED (mutex)
: PTHREAD_MUTEX_PSHARED (mutex));
int e = __futex_lock_pi64 (&mutex->__data.__lock, 0 /* ununsed */,
NULL, private);
if (e == ESRCH || e == EDEADLK)
{
assert (e != 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 (e != ESRCH || !robust);
/* Delay the thread indefinitely. */
while (1)
__futex_abstimed_wait64 (&(unsigned int){0}, 0,
0 /* ignored */, NULL, private);
}
oldval = mutex->__data.__lock;
assert (robust || (oldval & FUTEX_OWNER_DIED) == 0);
}
if (__glibc_unlikely (oldval & FUTEX_OWNER_DIED))
{
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;
/* We must not enqueue the mutex before we have acquired it.
Also see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
ENQUEUE_MUTEX_PI (mutex);
/* We need to clear op_pending after we enqueue the mutex. */
__asm ("" ::: "memory");
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;
futex_unlock_pi ((unsigned int *) &mutex->__data.__lock,
PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
/* To the kernel, this will be visible after the kernel has
acquired the mutex in the syscall. */
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
return ENOTRECOVERABLE;
}
mutex->__data.__count = 1;
if (robust)
{
/* We must not enqueue the mutex before we have acquired it.
Also see comments at ENQUEUE_MUTEX. */
__asm ("" ::: "memory");
ENQUEUE_MUTEX_PI (mutex);
/* We need to clear op_pending after we enqueue the mutex. */
__asm ("" ::: "memory");
THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
}
}
break;
#endif /* __NR_futex. */
case PTHREAD_MUTEX_PP_RECURSIVE_NP:
case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
case PTHREAD_MUTEX_PP_NORMAL_NP:
case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
{
/* See concurrency notes regarding __kind in struct __pthread_mutex_s
in sysdeps/nptl/bits/thread-shared-types.h. */
int kind = atomic_load_relaxed (&(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 (__glibc_unlikely (mutex->__data.__count + 1 == 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;
}
int 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)
futex_wait ((unsigned int * ) &mutex->__data.__lock,
ceilval | 2,
PTHREAD_MUTEX_PSHARED (mutex));
}
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
LIBC_PROBE (mutex_acquired, 1, mutex);
return 0;
}
#if PTHREAD_MUTEX_VERSIONS
libc_hidden_ver (___pthread_mutex_lock, __pthread_mutex_lock)
# ifndef SHARED
strong_alias (___pthread_mutex_lock, __pthread_mutex_lock)
# endif
versioned_symbol (libpthread, ___pthread_mutex_lock, pthread_mutex_lock,
GLIBC_2_0);
# if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_34)
compat_symbol (libpthread, ___pthread_mutex_lock, __pthread_mutex_lock,
GLIBC_2_0);
# endif
#endif /* PTHREAD_MUTEX_VERSIONS */
#ifdef NO_INCR
void
__pthread_mutex_cond_lock_adjust (pthread_mutex_t *mutex)
{
/* See concurrency notes regarding __kind in struct __pthread_mutex_s
in sysdeps/nptl/bits/thread-shared-types.h. */
int mutex_kind = atomic_load_relaxed (&(mutex->__data.__kind));
assert ((mutex_kind & PTHREAD_MUTEX_PRIO_INHERIT_NP) != 0);
assert ((mutex_kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP) == 0);
assert ((mutex_kind & PTHREAD_MUTEX_PSHARED_BIT) == 0);
/* Record the ownership. */
pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
mutex->__data.__owner = id;
if (mutex_kind == PTHREAD_MUTEX_PI_RECURSIVE_NP)
++mutex->__data.__count;
}
#endif