1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
|
/**
* @file
*
* @ingroup RTEMSScoreFutex
*
* @brief This source file contains the implementation of
* _Futex_Wait() and _Futex_Wake().
*/
/*
* Copyright (c) 2015, 2016 embedded brains GmbH. All rights reserved.
*
* embedded brains GmbH
* Dornierstr. 4
* 82178 Puchheim
* Germany
* <rtems@embedded-brains.de>
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.org/license/LICENSE.
*/
/**
* @defgroup RTEMSScoreFutex Futex Handler
*
* @ingroup RTEMSScore
*
* @brief This group contains the Futex Handler implementation.
*
* The behaviour of the futex operations is defined by Linux, see also:
*
* https://man7.org/linux/man-pages/man2/futex.2.html
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <sys/lock.h>
#include <errno.h>
#include <rtems/score/atomic.h>
#include <rtems/score/chainimpl.h>
#include <rtems/score/threadimpl.h>
#include <rtems/score/threadqimpl.h>
#define FUTEX_TQ_OPERATIONS &_Thread_queue_Operations_FIFO
typedef struct {
Thread_queue_Syslock_queue Queue;
} Futex_Control;
RTEMS_STATIC_ASSERT(
offsetof( Futex_Control, Queue )
== offsetof( struct _Futex_Control, _Queue ),
FUTEX_CONTROL_QUEUE
);
RTEMS_STATIC_ASSERT(
sizeof( Futex_Control ) == sizeof( struct _Futex_Control ),
FUTEX_CONTROL_SIZE
);
static Futex_Control *_Futex_Get( struct _Futex_Control *_futex )
{
return (Futex_Control *) _futex;
}
static Thread_Control *_Futex_Queue_acquire_critical(
Futex_Control *futex,
Thread_queue_Context *queue_context
)
{
Thread_Control *executing;
executing = _Thread_Executing;
_Thread_queue_Queue_acquire_critical(
&futex->Queue.Queue,
&executing->Potpourri_stats,
&queue_context->Lock_context.Lock_context
);
return executing;
}
static void _Futex_Queue_release(
Futex_Control *futex,
ISR_Level level,
Thread_queue_Context *queue_context
)
{
_Thread_queue_Queue_release_critical(
&futex->Queue.Queue,
&queue_context->Lock_context.Lock_context
);
_ISR_Local_enable( level );
}
/**
* @brief Performs the ``FUTEX_WAIT`` operation.
*
* @param[in, out] _futex is the futex object.
*
* @param[in] uaddr is the address to the futex state.
*
* @param val is the expected futex state value.
*
* @retval 0 Returns zero if the futex state is equal to the expected value.
* In this case the calling thread is enqueued on the thread queue of the
* futex object.
*
* @retval EAGAIN Returns EAGAIN if the futex state is not equal to the
* expected value.
*/
int _Futex_Wait( struct _Futex_Control *_futex, int *uaddr, int val )
{
Futex_Control *futex;
ISR_Level level;
Thread_queue_Context queue_context;
Thread_Control *executing;
int eno;
futex = _Futex_Get( _futex );
_Thread_queue_Context_initialize( &queue_context );
_Thread_queue_Context_ISR_disable( &queue_context, level );
executing = _Futex_Queue_acquire_critical( futex, &queue_context );
if ( *uaddr == val ) {
_Thread_queue_Context_set_thread_state(
&queue_context,
STATES_WAITING_FOR_FUTEX
);
_Thread_queue_Context_set_enqueue_do_nothing_extra( &queue_context );
_Thread_queue_Context_set_ISR_level( &queue_context, level );
_Thread_queue_Enqueue(
&futex->Queue.Queue,
FUTEX_TQ_OPERATIONS,
executing,
&queue_context
);
eno = 0;
} else {
_Futex_Queue_release( futex, level, &queue_context );
eno = EAGAIN;
}
return eno;
}
typedef struct {
Thread_queue_Context Base;
int count;
} Futex_Context;
static Thread_Control *_Futex_Flush_filter(
Thread_Control *the_thread,
Thread_queue_Queue *queue,
Thread_queue_Context *queue_context
)
{
Futex_Context *context;
context = (Futex_Context *) queue_context;
if ( context->count <= 0 ) {
return NULL;
}
--context->count;
return the_thread;
}
/**
* @brief Performs the ``FUTEX_WAKE`` operation.
*
* @param[in, out] _futex is the futex object.
*
* @param count is the maximum count of threads to wake up.
*
* @return Returns the count of woken up threads.
*/
int _Futex_Wake( struct _Futex_Control *_futex, int count )
{
Futex_Control *futex;
ISR_Level level;
Futex_Context context;
futex = _Futex_Get( _futex );
_Thread_queue_Context_initialize( &context.Base );
_Thread_queue_Context_ISR_disable( &context.Base, level );
_Futex_Queue_acquire_critical( futex, &context.Base );
/*
* For some synchronization objects like barriers the _Futex_Wake() must be
* called in the fast path. Normally there are no threads on the queue, so
* check this condition early.
*/
if ( RTEMS_PREDICT_TRUE( _Thread_queue_Is_empty( &futex->Queue.Queue ) ) ) {
_Futex_Queue_release( futex, level, &context.Base );
return 0;
}
context.count = count;
_Thread_queue_Context_set_ISR_level( &context.Base, level );
return (int) _Thread_queue_Flush_critical(
&futex->Queue.Queue,
FUTEX_TQ_OPERATIONS,
_Futex_Flush_filter,
&context.Base
);
}
|
