source: trunk/kernel/libk/rwlock.h @ 424

Last change on this file since 424 was 423, checked in by alain, 7 years ago

cosmetic
File size: 4.9 KB
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1/*
2 * rwlock.h - kernel read/write lock definition.
3 *
4 * Author   Alain Greiner    (2016)
5 *
6 * Copyright (c) UPMC Sorbonne Universites
7 *
8 * This file is part of ALMOS-MKH.
9 *
10 * ALMOS-MKH is free software; you can redistribute it and/or modify it
11 * under the terms of the GNU General Public License as published by
12 * the Free Software Foundation; version 2.0 of the License.
13 *
14 * ALMOS-MKH is distributed in the hope that it will be useful, but
15 * WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
17 * General Public License for more details.
18 *
19 * You should have received a copy of the GNU General Public License
20 * along with ALMOS-kernel; if not, write to the Free Software Foundation,
21 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
22 */
23
24#ifndef _RWLOCK_H_
25#define _RWLOCK_H_
26
27#include <kernel_config.h>
28#include <hal_types.h>
29#include <list.h>
30
31/*******************************************************************************************
32 * This structure defines a local rwlock, that supports several simultaneous read
33 * accesses, but only one write access. It implements a ticket based allocation policy.
34 * Both readers and writers must take a ticket before doing anything else, and access
35 * are done in same order as requests (for both read an write ).
36 * - A reader take the lock to atomically increments the registered readers count.
37 *   Then it release the lock and access the protected structure. It atomically decrement
38 *   the readers count without taking the lock when access is completed.
39 * - A writer take the lock and keep it, but must wait completion of all current read
40 *   accesses before starting its own access.
41 * As this local lock is only accessed by the local threads, if the lock is taken,
42 * the new-comers use a busy waiting policy with a delay between retry.
43 * TODO : Introduce the rwlocks in the list of locks taken by a given thread for debug.
44 ******************************************************************************************/
45
46/****     Forward declarations    ****/
47
48struct thread_s;
49
50/*******************************************************************************************
51 * This structure defines a local rwlock.
52 * The "owner" and "list" fields are used for debug.
53 ******************************************************************************************/
54
55typedef struct rwlock_s
56{
57        uint32_t            ticket;           /*! first free ticket index                     */
58    uint32_t            current;          /*! ticket index of current owner               */
59    uint32_t            count;            /*! number of simultaneous readers threads      */
60
61#if CONFIG_LOCKS_DEBUG
62        struct thread_s   * owner;            /*! pointer on curent writer thread             */
63    list_entry_t        list;             /*! member of list of locks taken by owner      */
64#endif
65
66}
67rwlock_t;
68
69/*******************************************************************************************
70 * This function initializes a local rwlock.
71 *******************************************************************************************
72 * @ lock       : pointer on rwlock
73 ******************************************************************************************/
74void rwlock_init( rwlock_t * lock );
75
76/*******************************************************************************************
77 * This function get access to a local rwlock for a reader.
78 *******************************************************************************************
79 * @ lock       : pointer on rwlock
80 ******************************************************************************************/
81void rwlock_rd_lock( rwlock_t * lock );
82
83/*******************************************************************************************
84 * This function get access to a local rwlock for a writer.
85 *******************************************************************************************
86 * @ lock       : pointer on rwlock
87 ******************************************************************************************/
88void rwlock_wr_lock( rwlock_t * lock );
89
90/*******************************************************************************************
91 * This function unlocks a local rwlock for a reader.
92 *******************************************************************************************
93 * @ lock       : pointer on rwlock
94 ******************************************************************************************/
95void rwlock_rd_unlock( rwlock_t * lock );
96
97/*******************************************************************************************
98 * This function unlocks a local rwlock for a writer.
99 *******************************************************************************************
100 * @ lock       : pointer on rwlock
101 ******************************************************************************************/
102void rwlock_wr_unlock( rwlock_t * lock );
103
104
105#endif  /* _RWLOCK_H_ */
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