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
|
/*
* File : lf_ring_buffer.c
* Author : Jérémy Zurcher <jeremy@asynk.ch>
* Date : 05/01/010
* License :
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
*/
#include "lf_ringbuffer.h"
#include "lf_portable_cas.h"
#include <stdlib.h>
#include <string.h>
#include <time.h>
//#define DEBUG_LFRB_KO 1
//#define DEBUG_LFRB_CAS 1
//#define DEBUG_LFRB 1
#ifdef DEBUG_LFRB
#include <stdio.h>
#define _LOG_KO_( ... ) fprintf(stdout,__VA_ARGS__)
#define _LOG_CAS_( ... )fprintf(stdout,__VA_ARGS__)
#elif defined DEBUG_LFRB_CAS
#include <stdio.h>
#define _LOG_KO_( ... )
#define _LOG_CAS_( ... )fprintf(stdout,__VA_ARGS__)
#elif defined DEBUG_LFRB_KO
#include <stdio.h>
#define _LOG_KO_( ... ) fprintf(stdout,__VA_ARGS__)
#define _LOG_CAS_( ... )
#else
#define _LOG_KO_( ... )
#define _LOG_CAS_( ... )
#endif
#define BACKOFF_NANO_SLEEP 10
#define USHORTMAX 0xffff
/* An unsigned int (indexes) is used to store both read_from and write_to indexes
* so that 32 bits compare and swap may be used to update both in one atomic instruction call.
* To be able to differenciate an empty buffer from a full buffer,
* read_from part of indexes is set to 0xffff (USHORTMAX) when the buffer is empty.
* Thus the maximum size of the buffer is 0xffff-1 = 65534 elements
*/
/* initialize an empty lf_ringbuffer struct */
lf_ringbuffer_t* lf_ringbuffer_create( size_t n_buf ) {
if(n_buf>=USHORTMAX) {
return NULL;
}
/* alloc ringbuffer struct */
lf_ringbuffer_t *r = malloc(sizeof(lf_ringbuffer_t));
if(r==NULL) return NULL;
/* alloc buffer */
r->buffer = malloc(LFRB_BUFFER_SIZE*n_buf);
if(r->buffer==NULL) {
free(r);
return NULL;
}
memset(r->buffer,0,LFRB_BUFFER_SIZE*n_buf);
r->n_buf = n_buf;
r->indexes = (unsigned int)(USHORTMAX<<16) | (unsigned int)0;
return r;
}
/* destroy an lf_ringbuffer strcture */
void lf_ringbuffer_destroy( lf_ringbuffer_t *r ) {
free(r->buffer);
free(r);
}
/* return 1 if is empty */
int lf_ringbuffer_empty( lf_ringbuffer_t *r ) { return (r->indexes>>16)==USHORTMAX; }
/* write data into the ring buffer */
int lf_ringbuffer_write( lf_ringbuffer_t *r, void *data, int flags ) {
unsigned int current, next;
unsigned int write_to, read_from;
struct timespec backoff;
int backoff_time = BACKOFF_NANO_SLEEP;
/* reserve a buffer */
for(;;){
/* copy indexes and split it */
current = r->indexes;
write_to = current&0xffff;
read_from = current>>16;
/*
* check if the buffer is available,
* if read_from==write_to the buffer is full
* if it is available and full, it means that a writer thread which reserved this buffer
* hadn't had enough CPU cycles to call MARK_AS_FILLED
*/
if( LFRB_IS_AVAILABLE( r->buffer[write_to] ) && read_from!=write_to ) {
next = write_to+1;
if (next==r->n_buf) next=0;
/* set read_from to write_to if needed */
if (read_from==USHORTMAX) {
next |= write_to<<16;
} else {
next |= read_from<<16;
}
/* try to update indexes */
_LOG_CAS_( "write: CAS %u %u %u\n", r->indexes, current, next );
if( CompareAndSwapInt( &r->indexes, current, next ) ) break;
} else {
_LOG_KO_("write: impossible : wt:%d rf:%d wa:%d\n",write_to,read_from,LFRB_IS_AVAILABLE(r->buffer[write_to]));
if(IS_NOT_BLOCKING(flags)) return -1;
}
/* sleep */
backoff.tv_sec = 0;
backoff.tv_nsec = backoff_time;
nanosleep(&backoff,NULL);
backoff_time += BACKOFF_NANO_SLEEP;
}
/* fill this buffer and mark it as filled */
memcpy( LFRB_DATA_PTR(r->buffer[write_to]), data, LFRB_DATA_SIZE );
LFRB_MARK_AS_FILLED( r->buffer[write_to] );
return 0;
}
/* read data from the ring buffer */
int lf_ringbuffer_read( lf_ringbuffer_t *r, void *data, int flags ) {
unsigned int current, next;
unsigned int write_to, read_from, tmp;
struct timespec backoff;
int backoff_time = BACKOFF_NANO_SLEEP;
for(;;) {
/* copy indexes and split it */
current = r->indexes;
write_to = current&0xffff;
read_from = current>>16;
/*
* the buffer may be non empty but available if a writer thread hadn't had enough CPU cycles to mark the buffer as filled
*/
if( read_from==USHORTMAX || LFRB_IS_AVAILABLE( r->buffer[read_from] ) ) {
_LOG_KO_("read : impossible : wt:%d rf:%d ra:%d\n",write_to,read_from,LFRB_IS_AVAILABLE(r->buffer[read_from]));
if(IS_NOT_BLOCKING(flags)) return -1;
} else {
tmp = read_from +1;
if (tmp==r->n_buf) tmp=0;
/* set the buffer empty if needed */
if (tmp==write_to) {
tmp = USHORTMAX;
}
next = tmp<<16 | write_to;
/* try to update indexes */
_LOG_CAS_( "read: CAS %u %u %u\n", r->indexes, current, next );
if( CompareAndSwapInt( &r->indexes, current , next ) ) break;
}
/* sleep */
backoff.tv_sec = 0;
backoff.tv_nsec = backoff_time;
nanosleep(&backoff,NULL);
backoff_time += BACKOFF_NANO_SLEEP;
}
/* copy this buffer and mark it as read */
memcpy( data, LFRB_DATA_PTR(r->buffer[read_from]), LFRB_DATA_SIZE );
LFRB_MARK_AS_READ( r->buffer[read_from] );
return 0;
}
|
