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/* Low-level lock implementation, x86 version.
Copyright (C) 2019 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
<http://www.gnu.org/licenses/>. */
#ifndef _X86_64_LOWLEVELLOCK_H
#define _X86_64_LOWLEVELLOCK_H 1
#ifndef __ASSEMBLER__
#include <sysdeps/nptl/lowlevellock.h>
#include <single-thread.h>
/* The lll_trylock, lll_lock, and lll_unlock implements a single-thread
optimization using the cmpxchgl instruction. It checks if the process
is single thread and avoid a more expensive atomic instruction. */
/* The single-thread optimization only works for libc itself, we need
atomicity for libpthread in case of shared futexes. */
#if !IS_IN(libc)
# define is_single_thread 0
#else
# define is_single_thread SINGLE_THREAD_P
#endif
/* In the __lllc_as we simply return the value in %eax after the cmpxchg
instruction. In case the operation succeeded this value is zero. In case
the operation failed, the cmpxchg instruction has loaded the current value
of the memory work which is guaranteed to be nonzero. */
static inline int
__attribute__ ((always_inline))
__lll_cas_lock (int *futex)
{
int ret;
asm volatile ("cmpxchgl %2, %1"
: "=a" (ret), "=m" (*futex)
: "r" (1), "m" (*futex), "0" (0)
: "memory");
return ret;
}
#undef lll_trylock
#define lll_trylock(lock) \
({ \
int __ret; \
if (is_single_thread) \
__ret = __lll_cas_lock (&(lock)); \
else \
__ret = __lll_trylock (&(lock)); \
__ret; \
})
#undef lll_lock
#define lll_lock(lock, private) \
((void) \
({ \
if (is_single_thread) \
__lll_cas_lock (&(lock)); \
else \
__lll_lock (&(lock), private); \
}))
#undef lll_unlock
#define lll_unlock(lock, private) \
((void) \
({ \
if (is_single_thread) \
(lock)--; \
else \
__lll_unlock (&(lock), private); \
}))
extern int __lll_timedlock_elision (int *futex, short *adapt_count,
const struct timespec *timeout,
int private) attribute_hidden;
#define lll_timedlock_elision(futex, adapt_count, timeout, private) \
__lll_timedlock_elision(&(futex), &(adapt_count), timeout, private)
extern int __lll_lock_elision (int *futex, short *adapt_count, int private)
attribute_hidden;
extern int __lll_unlock_elision (int *lock, int private)
attribute_hidden;
extern int __lll_trylock_elision (int *lock, short *adapt_count)
attribute_hidden;
#define lll_lock_elision(futex, adapt_count, private) \
__lll_lock_elision (&(futex), &(adapt_count), private)
#define lll_unlock_elision(futex, adapt_count, private) \
__lll_unlock_elision (&(futex), private)
#define lll_trylock_elision(futex, adapt_count) \
__lll_trylock_elision (&(futex), &(adapt_count))
#endif /* !__ASSEMBLER__ */
#endif /* lowlevellock.h */
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