projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| a334319f | 1 | /* Copyright (C) 2002 Free Software Foundation, Inc. |
| 76a50749 UD |
2 | This file is part of the GNU C Library. |
| 3 | Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. | |
| 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 | |
| 7 | License as published by the Free Software Foundation; either | |
| 8 | version 2.1 of the 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; if not, write to the Free | |
| 17 | Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA | |
| 18 | 02111-1307 USA. */ | |
| 19 | ||
| 20 | #include <atomic.h> | |
| 21 | ||
| 22 | ||
| 23 | /* Implement generic mutex. Basic futex syscall support is required: | |
| 24 | ||
| 25 | lll_futex_wait(futex, value) - call sys_futex with FUTEX_WAIT | |
| 26 | and third parameter VALUE | |
| 27 | ||
| 28 | lll_futex_wake(futex, value) - call sys_futex with FUTEX_WAKE | |
| 29 | and third parameter VALUE | |
| 30 | */ | |
| 31 | ||
| 32 | ||
| 33 | /* Mutex lock counter: | |
| 34 | bit 31 clear means unlocked; | |
| 35 | bit 31 set means locked. | |
| 36 | ||
| 37 | All code that looks at bit 31 first increases the 'number of | |
| 38 | interested threads' usage counter, which is in bits 0-30. | |
| 39 | ||
| 40 | All negative mutex values indicate that the mutex is still locked. */ | |
| 41 | ||
| 42 | ||
| 43 | static inline void | |
| 44 | __generic_mutex_lock (int *mutex) | |
| 45 | { | |
| 46 | unsigned int v; | |
| 47 | ||
| 48 | /* Bit 31 was clear, we got the mutex. (this is the fastpath). */ | |
| 49 | if (atomic_bit_test_set (mutex, 31) == 0) | |
| 50 | return; | |
| 51 | ||
| 52 | atomic_increment (mutex); | |
| 53 | ||
| 54 | while (1) | |
| 55 | { | |
| 56 | if (atomic_bit_test_set (mutex, 31) == 0) | |
| 57 | { | |
| 58 | atomic_decrement (mutex); | |
| 59 | return; | |
| 60 | } | |
| 61 | ||
| 62 | /* We have to wait now. First make sure the futex value we are | |
| 63 | monitoring is truly negative (i.e. locked). */ | |
| 64 | v = *mutex; | |
| 65 | if (v >= 0) | |
| 66 | continue; | |
| 67 | ||
| 68 | lll_futex_wait (mutex, v); | |
| 69 | } | |
| 70 | } | |
| 71 | ||
| 72 | ||
| 73 | static inline void | |
| 74 | __generic_mutex_unlock (int *mutex) | |
| 75 | { | |
| 76 | /* Adding 0x80000000 to the counter results in 0 if and only if | |
| 77 | there are not other interested threads - we can return (this is | |
| 78 | the fastpath). */ | |
| a334319f | 79 | if (atomic_add_zero (0x80000000, mutex)) |
| 76a50749 UD |
80 | return; |
| 81 | ||
| 82 | /* There are other threads waiting for this mutex, wake one of them | |
| 83 | up. */ | |
| 84 | lll_futex_wake (mutex, 1); | |
| 85 | } | |
| 86 | ||
| 87 | ||
| 88 | #define lll_mutex_lock(futex) __generic_mutex_lock (&(futex)) | |
| 89 | #define lll_mutex_unlock(futex) __generic_mutex_unlock (&(futex)) |