| yuezonghe | 824eb0c | 2024-06-27 02:32:26 -0700 | [diff] [blame^] | 1 | /* Low level locking macros used in NPTL implementation. Stub version. |
| 2 | Copyright (C) 2002, 2007 Free Software Foundation, Inc. |
| 3 | This file is part of the GNU C Library. |
| 4 | Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. |
| 5 | |
| 6 | The GNU C Library is free software; you can redistribute it and/or |
| 7 | modify it under the terms of the GNU Lesser General Public |
| 8 | License as published by the Free Software Foundation; either |
| 9 | version 2.1 of the License, or (at your option) any later version. |
| 10 | |
| 11 | The GNU C Library is distributed in the hope that it will be useful, |
| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 14 | Lesser General Public License for more details. |
| 15 | |
| 16 | You should have received a copy of the GNU Lesser General Public |
| 17 | License along with the GNU C Library; if not, write to the Free |
| 18 | Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
| 19 | 02111-1307 USA. */ |
| 20 | |
| 21 | #include <atomic.h> |
| 22 | |
| 23 | |
| 24 | /* Mutex lock counter: |
| 25 | bit 31 clear means unlocked; |
| 26 | bit 31 set means locked. |
| 27 | |
| 28 | All code that looks at bit 31 first increases the 'number of |
| 29 | interested threads' usage counter, which is in bits 0-30. |
| 30 | |
| 31 | All negative mutex values indicate that the mutex is still locked. */ |
| 32 | |
| 33 | |
| 34 | static inline void |
| 35 | __generic_mutex_lock (int *mutex) |
| 36 | { |
| 37 | unsigned int v; |
| 38 | |
| 39 | /* Bit 31 was clear, we got the mutex. (this is the fastpath). */ |
| 40 | if (atomic_bit_test_set (mutex, 31) == 0) |
| 41 | return; |
| 42 | |
| 43 | atomic_increment (mutex); |
| 44 | |
| 45 | while (1) |
| 46 | { |
| 47 | if (atomic_bit_test_set (mutex, 31) == 0) |
| 48 | { |
| 49 | atomic_decrement (mutex); |
| 50 | return; |
| 51 | } |
| 52 | |
| 53 | /* We have to wait now. First make sure the futex value we are |
| 54 | monitoring is truly negative (i.e. locked). */ |
| 55 | v = *mutex; |
| 56 | if (v >= 0) |
| 57 | continue; |
| 58 | |
| 59 | lll_futex_wait (mutex, v, |
| 60 | // XYZ check mutex flag |
| 61 | LLL_SHARED); |
| 62 | } |
| 63 | } |
| 64 | |
| 65 | |
| 66 | static inline void |
| 67 | __generic_mutex_unlock (int *mutex) |
| 68 | { |
| 69 | /* Adding 0x80000000 to the counter results in 0 if and only if |
| 70 | there are not other interested threads - we can return (this is |
| 71 | the fastpath). */ |
| 72 | if (atomic_add_zero (mutex, 0x80000000)) |
| 73 | return; |
| 74 | |
| 75 | /* There are other threads waiting for this mutex, wake one of them |
| 76 | up. */ |
| 77 | lll_futex_wake (mutex, 1, |
| 78 | // XYZ check mutex flag |
| 79 | LLL_SHARED); |
| 80 | } |
| 81 | |
| 82 | |
| 83 | #define lll_mutex_lock(futex) __generic_mutex_lock (&(futex)) |
| 84 | #define lll_mutex_unlock(futex) __generic_mutex_unlock (&(futex)) |