diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/x86/lowlevellock.h')
| -rw-r--r-- | sysdeps/unix/sysv/linux/x86/lowlevellock.h | 110 |
1 files changed, 110 insertions, 0 deletions
diff --git a/sysdeps/unix/sysv/linux/x86/lowlevellock.h b/sysdeps/unix/sysv/linux/x86/lowlevellock.h new file mode 100644 index 0000000000..8a78dcff47 --- /dev/null +++ b/sysdeps/unix/sysv/linux/x86/lowlevellock.h @@ -0,0 +1,110 @@ +/* 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 */ |