| 1 | /* |
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| 2 | * rwlock.h - kernel read/write lock definition. |
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| 3 | * |
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| 4 | * Author Alain Greiner (2016) |
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| 5 | * |
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| 6 | * Copyright (c) UPMC Sorbonne Universites |
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| 7 | * |
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| 8 | * This file is part of ALMOS-MKH. |
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| 9 | * |
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| 10 | * ALMOS-MKH is free software; you can redistribute it and/or modify it |
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| 11 | * under the terms of the GNU General Public License as published by |
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| 12 | * the Free Software Foundation; version 2.0 of the License. |
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| 13 | * |
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| 14 | * ALMOS-MKH is distributed in the hope that it will be useful, but |
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| 15 | * WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 16 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 17 | * General Public License for more details. |
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| 18 | * |
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| 19 | * You should have received a copy of the GNU General Public License |
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| 20 | * along with ALMOS-kernel; if not, write to the Free Software Foundation, |
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| 21 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA |
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| 22 | */ |
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| 23 | |
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| 24 | #ifndef _RWLOCK_H_ |
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| 25 | #define _RWLOCK_H_ |
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| 26 | |
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| 27 | #include <almos_config.h> |
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| 28 | #include <hal_types.h> |
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| 29 | |
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| 30 | /******************************************************************************************* |
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| 31 | * This structure defines a local rwlock, that supports several simultaneous read |
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| 32 | * accesses, but only one write access. It implements a ticket based allocation policy. |
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| 33 | * Both readers and writers must take a ticket before doing anything else, and access |
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| 34 | * are done in same order as requests (for both read an write ). |
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| 35 | * - A reader take the lock to atomically increments the registered readers count. |
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| 36 | * Then it release the lock and access the protected structure. It atomically decrement |
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| 37 | * the readers count without taking the lock when access is completed. |
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| 38 | * - A writer take the lock and keep it, but must wait completion of all current read |
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| 39 | * accesses before starting its own access. |
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| 40 | * As this local lock is only accessed by the local threads, if the lock is taken, |
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| 41 | * the new-comers use a busy waiting policy with a delay between retry. |
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| 42 | ******************************************************************************************/ |
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| 43 | |
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| 44 | /**** Forward declarations ****/ |
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| 45 | |
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| 46 | struct thread_s; |
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| 47 | |
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| 48 | /******************************************************************************************* |
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| 49 | * This structure defines a local rwlock. |
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| 50 | ******************************************************************************************/ |
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| 51 | |
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| 52 | typedef struct rwlock_s |
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| 53 | { |
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| 54 | uint32_t ticket; /*! first free ticket index */ |
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| 55 | uint32_t current; /*! ticket index of current owner */ |
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| 56 | uint32_t count; /*! number of simultaneous readers threads */ |
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| 57 | struct thread_s * owner; /*! pointer on curent writer thread */ |
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| 58 | } |
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| 59 | rwlock_t; |
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| 60 | |
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| 61 | /******************************************************************************************* |
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| 62 | * This function initializes a local rwlock. |
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| 63 | ******************************************************************************************* |
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| 64 | * @ lock : pointer on rwlock |
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| 65 | ******************************************************************************************/ |
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| 66 | void rwlock_init( rwlock_t * lock ); |
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| 67 | |
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| 68 | /******************************************************************************************* |
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| 69 | * This function get access to a local rwlock for a reader. |
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| 70 | ******************************************************************************************* |
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| 71 | * @ lock : pointer on rwlock |
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| 72 | ******************************************************************************************/ |
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| 73 | void rwlock_rd_lock( rwlock_t * lock ); |
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| 74 | |
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| 75 | /******************************************************************************************* |
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| 76 | * This function get access to a local rwlock for a writer. |
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| 77 | ******************************************************************************************* |
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| 78 | * @ lock : pointer on rwlock |
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| 79 | ******************************************************************************************/ |
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| 80 | void rwlock_wr_lock( rwlock_t * lock ); |
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| 81 | |
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| 82 | /******************************************************************************************* |
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| 83 | * This function unlocks a local rwlock for a reader. |
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| 84 | ******************************************************************************************* |
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| 85 | * @ lock : pointer on rwlock |
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| 86 | ******************************************************************************************/ |
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| 87 | void rwlock_rd_unlock( rwlock_t * lock ); |
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| 88 | |
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| 89 | /******************************************************************************************* |
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| 90 | * This function unlocks a local rwlock for a writer. |
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| 91 | ******************************************************************************************* |
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| 92 | * @ lock : pointer on rwlock |
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| 93 | ******************************************************************************************/ |
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| 94 | void rwlock_wr_unlock( rwlock_t * lock ); |
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| 95 | |
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| 96 | |
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| 97 | #endif /* _RWLOCK_H_ */ |
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