source: trunk/kernel/libk/busylock.h

Last change on this file was 666, checked in by alain, 13 months ago

Cosmetic.

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[563]1/*
2 * busylock.h: local kernel busy-waiting lock definition.     
3 *
[666]4 * Authors  Alain Greiner (2016,2017,2018,2019,2020)
[563]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 _BUSYLOCK_H_
25#define _BUSYLOCK_H_
26
27#include <kernel_config.h>
28#include <hal_kernel_types.h>
29#include <hal_shared_types.h>
30#include <xlist.h>
31
32/*******************************************************************************************
33 * This synchronisation object sequencializes all concurrent read or write accesses to
34 * a shared object located in a given cluster, made by thread(s) running in same cluster.
35 * It uses a busy waiting policy when the lock is taken by another thread, and should
[624]36 * be used to execute very short actions, such as accessing basic allocators or higher
[623]37 * level synchronisation objects (barriers, queuelocks, or rwlocks).
[563]38 *
39 * - To acquire the lock, we use a ticket policy to avoid starvation: the calling thread
40 *   makes an atomic increment on a "ticket" allocator, and keep polling the "current"
41 *   value  until current == ticket.
42 *
[624]43 * - To release the lock, the owner thread increments the "current" value.
[563]44 *
[624]45 * - When a thread takes a busylock, it enters a critical section: the acquire()
[563]46 *   function disables the IRQs, takes the lock, increments the thread busylocks counter,
[624]47 *   save the SR in lock descriptor and returns.
[563]48 *
[624]49 * - The release() function releases the lock, decrements the thread busylock
50 *   counter, restores the SR to exit the critical section, and returns.
[563]51 *
[624]52 * WARNING: a thread cannot yield when it is holding a busylock (local or remote).
53 *
54 * This rule is checked by all functions containing a thread_yield() AND by the scheduler,
55 * thanks to the busylocks counter stored in the calling thread descriptor.
56 * 1) all functions call "thread_assert_can_yield()" before calling "thread_yield()".
57 * 2) The scheduler checks that the calling thread does not hold any busylock.
58 * In case of violation the core goes to sleep after a [PANIC] message on TXT0.
[563]59 ******************************************************************************************/
60
61/*******************************************************************************************
62 * This structure defines a busylock.
[624]63 * The <xlist> field is only used when DEBUG_BUSYLOCK is set.
64 * The <type> field defines the lock usage as detailed in the kernel_config.h file.
[563]65******************************************************************************************/
66
67typedef struct busylock_s
68{
69        uint32_t            ticket;      /*! next free ticket index                           */
70    volatile uint32_t   current;     /*! current owner index                              */
71    uint32_t            type;        /*! lock type for debug                              */
72    reg_t               save_sr;     /*! SR value                                         */
73
[666]74#if DEBUG_BUSYLOCK_TYPE
[563]75    xlist_entry_t       xlist;       /*! member of list of locks taken by same thread     */
76#endif
77
78}
79busylock_t;
80
81/*******************************************************************************************
82 * This function initializes a busylock.
83 *******************************************************************************************
84 * @ lock    : local pointer on busylock.
85 * @ type    : lock  type for debug.
86 ******************************************************************************************/
87void busylock_init( busylock_t * lock,
88                    uint32_t    type );
89
90/*******************************************************************************************
91 * This blocking function uses a busy waiting strategy to acquire a busylock.
92 * It makes an atomic increment on the "ticket" field to get a ticket value and increment
93 * the ticket allocator.
94 * Then it polls the "current" field until (current == ticket), and returns.
95 *******************************************************************************************
96 * @ lock    : local pointer on busylock.
97 ******************************************************************************************/
98void busylock_acquire( busylock_t * lock );
99
100/*******************************************************************************************
101 * This function releases a busylock by incrementing the "current" field.
102 *******************************************************************************************
103 * @ lock    : local pointer on busylock.
104 ******************************************************************************************/
105void busylock_release( busylock_t * lock );
106
107#endif  /* _BUSYLOCK_H_ */
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