| 1 | /* |
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| 2 | * readlock.h - kernel readlock 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 _READLOCK_H_ |
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| 25 | #define _READLOCK_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 readlock, that supports several simultaneous read |
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| 32 | * accesses, but only one write access. |
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| 33 | * - A reader does not take the exclusive ownership of the lock, but it must atomically |
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| 34 | * increment the registered readers count in the readlock_t structure before starting |
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| 35 | * access and decrement it when access is completed. |
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| 36 | * - A writer must take exclusive ownership before access, and must wait completion |
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| 37 | * of all current read access before starting its own access. |
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| 38 | * TODO : add a "list" field to register a taken lock in the owner thread list. |
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| 39 | ******************************************************************************************/ |
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| 40 | |
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| 41 | /**** Forward declarations ****/ |
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| 42 | |
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| 43 | struct thread_s; |
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| 44 | |
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| 45 | /******************************************************************************************* |
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| 46 | * This structure defines a local readlock. |
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| 47 | ******************************************************************************************/ |
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| 48 | |
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| 49 | typedef struct readlock_s |
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| 50 | { |
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| 51 | volatile uint32_t taken; /*! state : free if zero / taken if non zero */ |
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| 52 | volatile uint32_t count; /*! current number of readers */ |
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| 53 | struct thread_s * owner; /*! pointer on curent owner thread */ |
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| 54 | } |
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| 55 | readlock_t; |
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| 56 | |
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| 57 | /******************************************************************************************* |
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| 58 | * This function initializes a local readlock. |
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| 59 | ******************************************************************************************* |
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| 60 | * @ lock : pointer on readlock |
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| 61 | ******************************************************************************************/ |
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| 62 | void readlock_init( readlock_t * lock ); |
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| 63 | |
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| 64 | /******************************************************************************************* |
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| 65 | * This function get access to a local readlock for a reader. |
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| 66 | ******************************************************************************************* |
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| 67 | * @ lock : pointer on readlock |
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| 68 | ******************************************************************************************/ |
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| 69 | void readlock_rd_lock( readlock_t * lock ); |
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| 70 | |
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| 71 | /******************************************************************************************* |
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| 72 | * This function get access to a local readlock for a writer. |
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| 73 | ******************************************************************************************* |
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| 74 | * @ lock : pointer on readlock |
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| 75 | ******************************************************************************************/ |
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| 76 | void readlock_wr_lock( readlock_t * lock ); |
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| 77 | |
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| 78 | /******************************************************************************************* |
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| 79 | * This function unlocks a local readlock for a reader. |
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| 80 | ******************************************************************************************* |
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| 81 | * @ lock : pointer on readlock |
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| 82 | ******************************************************************************************/ |
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| 83 | void readlock_rd_unlock( readlock_t * lock ); |
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| 84 | |
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| 85 | /******************************************************************************************* |
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| 86 | * This function unlocks a local readlock for a writer. |
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| 87 | ******************************************************************************************* |
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| 88 | * @ lock : pointer on readlock |
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| 89 | ******************************************************************************************/ |
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| 90 | void readlock_wr_unlock( readlock_t * lock ); |
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| 91 | |
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| 92 | |
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| 93 | #endif /* _READLOCK_H_ */ |
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