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0f550417 | 1 | /* POSIX spinlock implementation. x86 version. |
0950889b | 2 | Copyright (C) 2000, 2002 Free Software Foundation, Inc. |
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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 | |
cc7375ce RM |
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 | |
0f550417 UD |
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 | |
cc7375ce | 13 | Lesser General Public License for more details. |
0f550417 | 14 | |
cc7375ce | 15 | You should have received a copy of the GNU Lesser General Public |
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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> | |
27ee0a55 | 22 | #include "internals.h" |
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23 | #include "kernel-features.h" |
24 | ||
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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) | |
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100 | |
101 | #ifndef __ASSUME_SET_THREAD_AREA_SYSCALL | |
102 | int __have_no_set_thread_area; | |
103 | #endif |