| 1 | /* |
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| 2 | * remote_rwlock.h - kernel remote_rwlock definition. |
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| 3 | * |
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| 4 | * Authors 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-MKH; 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 _REMOTE_RWLOCK_H_ |
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| 25 | #define _REMOTE_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 | #include <xlist.h> |
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| 30 | |
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| 31 | /*************************************************************************************** |
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| 32 | * This structure defines a remote rwdlock,that supports several simultaneous read |
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| 33 | * accesses, but only one write access. It implements a ticket based allocation policy. |
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| 34 | * It can be used to synchronize threads running in different clusters, because |
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| 35 | * all access functions use remote pointers. |
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| 36 | * - A reader take the lock to atomically increments the registered readers count. |
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| 37 | * Then it release the lock and access the protected structure. It atomically |
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| 38 | * decrements the readers count without taking the lock when access is completed. |
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| 39 | * - A writer take the lock and keep it, but must wait completion of all current read |
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| 40 | * accesses before starting its own access. |
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| 41 | * When the lock is taken by another thread, the new-comers use a busy waiting policy. |
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| 42 | * |
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| 43 | * TODO This could be replaced by a descheduling policy and a threads waiting queue |
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| 44 | * implemented in the lock itself: each thread releasing the lock (i.e. incrementing |
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| 45 | * the current field) activates the first waiting thread... |
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| 46 | **************************************************************************************/ |
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| 47 | |
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| 48 | typedef struct remote_rwlock_s |
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| 49 | { |
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| 50 | uint32_t ticket; /*! first free ticket index */ |
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| 51 | uint32_t current; /*! ticket index of current owner */ |
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| 52 | uint32_t count; /*! current number of reader threads */ |
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| 53 | xptr_t owner; /*! extended pointer on writer thread */ |
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| 54 | } |
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| 55 | remote_rwlock_t; |
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| 56 | |
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| 57 | /*************************************************************************************** |
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| 58 | * This function initializes a remote rwlock. |
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| 59 | *************************************************************************************** |
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| 60 | * @ lock_xp : extended pointer on the remote rwlock |
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| 61 | **************************************************************************************/ |
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| 62 | void remote_rwlock_init( xptr_t lock_xp ); |
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| 63 | |
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| 64 | /*************************************************************************************** |
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| 65 | * This blocking function get access to a remote rwlock for a reader. |
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| 66 | * It increments the calling thread locks count when the lock has been taken. |
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| 67 | *************************************************************************************** |
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| 68 | * @ lock_xp : extended pointer on the remote rwlock |
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| 69 | **************************************************************************************/ |
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| 70 | void remote_rwlock_rd_lock( xptr_t lock_xp ); |
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| 71 | |
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| 72 | /*************************************************************************************** |
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| 73 | * This function releases a remote rwlock for a reader. |
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| 74 | * It decrements the calling thread locks count when the lock has been released. |
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| 75 | *************************************************************************************** |
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| 76 | * @ lock_xp : extended pointer on the remote rwlock |
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| 77 | **************************************************************************************/ |
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| 78 | void remote_rwlock_rd_unlock( xptr_t lock_xp ); |
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| 79 | |
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| 80 | /*************************************************************************************** |
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| 81 | * This blocking function get access to a remote rwlock for a writer. |
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| 82 | * It increments the calling thread locks count when the lock has been taken. |
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| 83 | *************************************************************************************** |
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| 84 | * @ lock_xp : extended pointer on the remote rwlock |
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| 85 | **************************************************************************************/ |
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| 86 | void remote_rwlock_wr_lock( xptr_t lock_xp ); |
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| 87 | |
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| 88 | /*************************************************************************************** |
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| 89 | * This function releases a remote rwlock for a writer. |
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| 90 | * It decrements the calling thread locks count when the lock has been released. |
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| 91 | *************************************************************************************** |
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| 92 | * @ lock_xp : extended pointer on the remote rwlock |
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| 93 | **************************************************************************************/ |
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| 94 | void remote_rwlock_wr_unlock( xptr_t lock_xp ); |
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| 95 | |
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| 96 | #endif |
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