/* POSIX spinlock implementation. x86 version.
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/* POSIX spinlock implementation. x86 version.
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Copyright (C) 2000 Free Software Foundation, Inc.
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Copyright (C) 2000 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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License along with the GNU C Library; see the file COPYING.LIB. If not,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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Boston, MA 02111-1307, USA. */
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Boston, MA 02111-1307, USA. */
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#include <errno.h>
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#include <errno.h>
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#include <pthread.h>
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#include <pthread.h>
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#include "internals.h"
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#include "internals.h"
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/* This implementation is similar to the one used in the Linux kernel.
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/* This implementation is similar to the one used in the Linux kernel.
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But the kernel is byte instructions for the memory access. This is
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But the kernel is byte instructions for the memory access. This is
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faster but unusable here. The problem is that only 128
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faster but unusable here. The problem is that only 128
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threads/processes could use the spinlock at the same time. If (by
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threads/processes could use the spinlock at the same time. If (by
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a design error in the program) a thread/process would hold the
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a design error in the program) a thread/process would hold the
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spinlock for a time long enough to accumulate 128 waiting
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spinlock for a time long enough to accumulate 128 waiting
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processes, the next one will find a positive value in the spinlock
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processes, the next one will find a positive value in the spinlock
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and assume it is unlocked. We cannot accept that. */
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and assume it is unlocked. We cannot accept that. */
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int
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int
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__pthread_spin_lock (pthread_spinlock_t *lock)
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__pthread_spin_lock (pthread_spinlock_t *lock)
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{
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{
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asm volatile
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asm volatile
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("\n"
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("\n"
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"1:\n\t"
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"1:\n\t"
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"lock; decl %0\n\t"
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"lock; decl %0\n\t"
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"js 2f\n\t"
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"js 2f\n\t"
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".section .text.spinlock,\"ax\"\n"
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".section .text.spinlock,\"ax\"\n"
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"2:\n\t"
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"2:\n\t"
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"cmpl $0,%0\n\t"
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"cmpl $0,%0\n\t"
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"rep; nop\n\t"
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"rep; nop\n\t"
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"jle 2b\n\t"
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"jle 2b\n\t"
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"jmp 1b\n\t"
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"jmp 1b\n\t"
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".previous"
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".previous"
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: "=m" (*lock));
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: "=m" (*lock));
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return 0;
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return 0;
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}
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}
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weak_alias (__pthread_spin_lock, pthread_spin_lock)
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weak_alias (__pthread_spin_lock, pthread_spin_lock)
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int
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int
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__pthread_spin_trylock (pthread_spinlock_t *lock)
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__pthread_spin_trylock (pthread_spinlock_t *lock)
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{
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{
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int oldval;
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int oldval;
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asm volatile
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asm volatile
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("xchgl %0,%1"
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("xchgl %0,%1"
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: "=r" (oldval), "=m" (*lock)
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: "=r" (oldval), "=m" (*lock)
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: "0" (0));
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: "0" (0));
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return oldval > 0 ? 0 : EBUSY;
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return oldval > 0 ? 0 : EBUSY;
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}
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}
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weak_alias (__pthread_spin_trylock, pthread_spin_trylock)
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weak_alias (__pthread_spin_trylock, pthread_spin_trylock)
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int
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int
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__pthread_spin_unlock (pthread_spinlock_t *lock)
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__pthread_spin_unlock (pthread_spinlock_t *lock)
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{
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{
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asm volatile
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asm volatile
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("movl $1,%0"
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("movl $1,%0"
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: "=m" (*lock));
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: "=m" (*lock));
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return 0;
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return 0;
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}
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}
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weak_alias (__pthread_spin_unlock, pthread_spin_unlock)
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weak_alias (__pthread_spin_unlock, pthread_spin_unlock)
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int
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int
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__pthread_spin_init (pthread_spinlock_t *lock, int pshared)
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__pthread_spin_init (pthread_spinlock_t *lock, int pshared)
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{
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{
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/* We can ignore the `pshared' parameter. Since we are busy-waiting
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/* We can ignore the `pshared' parameter. Since we are busy-waiting
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all processes which can access the memory location `lock' points
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all processes which can access the memory location `lock' points
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to can use the spinlock. */
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to can use the spinlock. */
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*lock = 1;
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*lock = 1;
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return 0;
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return 0;
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}
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}
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weak_alias (__pthread_spin_init, pthread_spin_init)
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weak_alias (__pthread_spin_init, pthread_spin_init)
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int
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int
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__pthread_spin_destroy (pthread_spinlock_t *lock)
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__pthread_spin_destroy (pthread_spinlock_t *lock)
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{
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{
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/* Nothing to do. */
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/* Nothing to do. */
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return 0;
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return 0;
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}
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}
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weak_alias (__pthread_spin_destroy, pthread_spin_destroy)
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weak_alias (__pthread_spin_destroy, pthread_spin_destroy)
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