| yuezonghe | 824eb0c | 2024-06-27 02:32:26 -0700 | [diff] [blame] | 1 | /* Copyright (C) 2002, 2007, 2009 Free Software Foundation, Inc. |
| 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 "pthreadP.h" |
| 21 | #include <bits/kernel-features.h> |
| 22 | #include <string.h> |
| 23 | |
| 24 | static const struct pthread_rwlockattr default_attr = |
| 25 | { |
| 26 | .lockkind = PTHREAD_RWLOCK_DEFAULT_NP, |
| 27 | .pshared = PTHREAD_PROCESS_PRIVATE |
| 28 | }; |
| 29 | |
| 30 | |
| 31 | int |
| 32 | __pthread_rwlock_init ( |
| 33 | pthread_rwlock_t *rwlock, |
| 34 | const pthread_rwlockattr_t *attr) |
| 35 | { |
| 36 | const struct pthread_rwlockattr *iattr; |
| 37 | |
| 38 | iattr = ((const struct pthread_rwlockattr *) attr) ?: &default_attr; |
| 39 | |
| 40 | memset (rwlock, '\0', sizeof (*rwlock)); |
| 41 | |
| 42 | rwlock->__data.__flags |
| 43 | = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP; |
| 44 | |
| 45 | /* The __SHARED field is computed to minimize the work that needs to |
| 46 | be done while handling the futex. There are two inputs: the |
| 47 | availability of private futexes and whether the rwlock is shared |
| 48 | or private. Unfortunately the value of a private rwlock is |
| 49 | fixed: it must be zero. The PRIVATE_FUTEX flag has the value |
| 50 | 0x80 in case private futexes are available and zero otherwise. |
| 51 | This leads to the following table: |
| 52 | |
| 53 | | pshared | result |
| 54 | | shared private | shared private | |
| 55 | ------------+-----------------+-----------------+ |
| 56 | !avail 0 | 0 0 | 0 0 | |
| 57 | avail 0x80 | 0x80 0 | 0 0x80 | |
| 58 | |
| 59 | If the pshared value is in locking functions XORed with avail |
| 60 | we get the expected result. */ |
| 61 | #ifdef __ASSUME_PRIVATE_FUTEX |
| 62 | rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE |
| 63 | ? 0 : FUTEX_PRIVATE_FLAG); |
| 64 | #else |
| 65 | rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE |
| 66 | ? 0 |
| 67 | : THREAD_GETMEM (THREAD_SELF, |
| 68 | header.private_futex)); |
| 69 | #endif |
| 70 | |
| 71 | return 0; |
| 72 | } |
| 73 | strong_alias (__pthread_rwlock_init, pthread_rwlock_init) |