| yuezonghe | 824eb0c | 2024-06-27 02:32:26 -0700 | [diff] [blame] | 1 | /* POSIX spinlock implementation. x86 version. |
| 2 | Copyright (C) 2000, 2002, 2006 Free Software Foundation, Inc. |
| 3 | This file is part of the GNU C Library. |
| 4 | |
| 5 | The GNU C Library is free software; you can redistribute it and/or |
| 6 | modify it under the terms of the GNU Lesser General Public License as |
| 7 | published by the Free Software Foundation; either version 2.1 of the |
| 8 | License, or (at your option) any later version. |
| 9 | |
| 10 | The GNU C Library is distributed in the hope that it will be useful, |
| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 13 | Lesser General Public License for more details. |
| 14 | |
| 15 | You should have received a copy of the GNU Lesser General Public |
| 16 | License along with the GNU C Library; see the file COPYING.LIB. If not, |
| 17 | write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
| 18 | Boston, MA 02111-1307, USA. */ |
| 19 | |
| 20 | #include <errno.h> |
| 21 | #include <pthread.h> |
| 22 | #include "internals.h" |
| 23 | #include <bits/kernel-features.h> |
| 24 | |
| 25 | |
| 26 | /* This implementation is similar to the one used in the Linux kernel. |
| 27 | But the kernel is byte instructions for the memory access. This is |
| 28 | faster but unusable here. The problem is that only 128 |
| 29 | threads/processes could use the spinlock at the same time. If (by |
| 30 | a design error in the program) a thread/process would hold the |
| 31 | spinlock for a time long enough to accumulate 128 waiting |
| 32 | processes, the next one will find a positive value in the spinlock |
| 33 | and assume it is unlocked. We cannot accept that. */ |
| 34 | |
| 35 | int |
| 36 | __pthread_spin_lock (pthread_spinlock_t *lock) |
| 37 | { |
| 38 | __asm__ __volatile__ |
| 39 | ("\n" |
| 40 | "1:\n\t" |
| 41 | "lock; decl %0\n\t" |
| 42 | "js 2f\n\t" |
| 43 | ".section .text.spinlock,\"ax\"\n" |
| 44 | "2:\n\t" |
| 45 | "cmpl $0,%0\n\t" |
| 46 | "rep; nop\n\t" |
| 47 | "jle 2b\n\t" |
| 48 | "jmp 1b\n\t" |
| 49 | ".previous" |
| 50 | : "=m" (*lock)); |
| 51 | return 0; |
| 52 | } |
| 53 | weak_alias (__pthread_spin_lock, pthread_spin_lock) |
| 54 | |
| 55 | |
| 56 | int |
| 57 | __pthread_spin_trylock (pthread_spinlock_t *lock) |
| 58 | { |
| 59 | int oldval; |
| 60 | |
| 61 | __asm__ __volatile__ |
| 62 | ("xchgl %0,%1" |
| 63 | : "=r" (oldval), "=m" (*lock) |
| 64 | : "0" (0)); |
| 65 | return oldval > 0 ? 0 : EBUSY; |
| 66 | } |
| 67 | weak_alias (__pthread_spin_trylock, pthread_spin_trylock) |
| 68 | |
| 69 | |
| 70 | int |
| 71 | __pthread_spin_unlock (pthread_spinlock_t *lock) |
| 72 | { |
| 73 | __asm__ __volatile__ |
| 74 | ("movl $1,%0" |
| 75 | : "=m" (*lock)); |
| 76 | return 0; |
| 77 | } |
| 78 | weak_alias (__pthread_spin_unlock, pthread_spin_unlock) |
| 79 | |
| 80 | |
| 81 | int |
| 82 | __pthread_spin_init (pthread_spinlock_t *lock, int pshared) |
| 83 | { |
| 84 | /* We can ignore the `pshared' parameter. Since we are busy-waiting |
| 85 | all processes which can access the memory location `lock' points |
| 86 | to can use the spinlock. */ |
| 87 | *lock = 1; |
| 88 | return 0; |
| 89 | } |
| 90 | weak_alias (__pthread_spin_init, pthread_spin_init) |
| 91 | |
| 92 | |
| 93 | int |
| 94 | __pthread_spin_destroy (pthread_spinlock_t *lock) |
| 95 | { |
| 96 | /* Nothing to do. */ |
| 97 | return 0; |
| 98 | } |
| 99 | weak_alias (__pthread_spin_destroy, pthread_spin_destroy) |
| 100 | |
| 101 | #ifndef __ASSUME_SET_THREAD_AREA_SYSCALL |
| 102 | int __have_no_set_thread_area; |
| 103 | #endif |