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
|
/****************************************************************************
NAME
libgps_shm.c - reasder access to shared-memory export
DESCRIPTION
This is a very lightweight alternative to JSON-over-sockets. Clients
won't be able to filter by device, and won't get device activation/deactivation
notifications. But both client and daemon will avoid all the marshalling and
unmarshalling overhead.
PERMISSIONS
This file is Copyright (c) 2010 by the GPSD project
BSD terms apply: see the file COPYING in the distribution root for details.
***************************************************************************/
#include "gpsd_config.h"
#ifdef SHM_EXPORT_ENABLE
#include <stddef.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/time.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include "gpsd.h"
#include "libgps.h"
/*@-matchfields@*/
struct privdata_t
{
void *shmseg;
int tick;
};
/*@+matchfields@*/
int gps_shm_open(/*@out@*/struct gps_data_t *gpsdata)
/* open a shared-memory connection to the daemon */
{
int shmid;
/*@-nullpass@*/
int shmkey = getenv("GPSD_SHM_KEY") ? atoi(getenv("GPSD_SHM_KEY")) : GPSD_KEY;
/*@+nullpass@*/
libgps_debug_trace((DEBUG_CALLS, "gps_shm_open()\n"));
gpsdata->privdata = NULL;
shmid = shmget((key_t)shmkey, sizeof(struct gps_data_t), 0);
if (shmid == -1) {
/* daemon isn't running or failed to create shared segment */
return -1;
}
gpsdata->privdata = (void *)malloc(sizeof(struct privdata_t));
if (gpsdata->privdata == NULL)
return -1;
PRIVATE(gpsdata)->shmseg = shmat(shmid, 0, 0);
if ((int)(long)gpsdata->privdata == -1) {
/* attach failed for sume unknown reason */
return -2;
}
#ifndef USE_QT
gpsdata->gps_fd = SHM_PSEUDO_FD;
#else
gpsdata->gps_fd = (void *)(intptr_t)SHM_PSEUDO_FD;
#endif /* USE_QT */
return 0;
}
bool gps_shm_waiting(const struct gps_data_t *gpsdata, int timeout)
/* check to see if new data has been written */
{
volatile struct shmexport_t *shared = (struct shmexport_t *)PRIVATE(gpsdata)->shmseg;
timestamp_t basetime = timestamp();
/* busy-waiting sucks, but there's not really an alternative */
for (;;) {
bool newdata = false;
memory_barrier();
if (shared->bookend1 == shared->bookend2 && shared->bookend1 > PRIVATE(gpsdata)->tick)
newdata = true;
memory_barrier();
if (newdata || (timestamp() - basetime >= (double)timeout))
break;
}
return true;
}
int gps_shm_read(struct gps_data_t *gpsdata)
/* read an update from the shared-memory segment */
{
/*@ -compdestroy */
if (gpsdata->privdata == NULL)
return -1;
else
{
int before, after;
void *private_save = gpsdata->privdata;
volatile struct shmexport_t *shared = (struct shmexport_t *)PRIVATE(gpsdata)->shmseg;
struct gps_data_t noclobber;
/*
* Following block of instructions must not be reordered,
* otherwise havoc will ensue. The memory_barrier() call
* should prevent reordering of the data accesses.
*
* This is a simple optimistic-concurrency technique. We wrote
* the second bookend first, then the data, then the first bookend.
* Reader copies what it sees in normal order; that way, if we
* start to write the segment during the read, the second bookend will
* get clobbered first and the data can be detected as bad.
*/
before = shared->bookend1;
memory_barrier();
(void)memcpy((void *)&noclobber,
(void *)&shared->gpsdata,
sizeof(struct gps_data_t));
memory_barrier();
after = shared->bookend2;
if (before != after)
return 0;
else {
(void)memcpy((void *)gpsdata,
(void *)&noclobber,
sizeof(struct gps_data_t));
/*@i1@*/gpsdata->privdata = private_save;
PRIVATE(gpsdata)->tick = after;
if ((gpsdata->set & REPORT_IS)!=0) {
if (gpsdata->fix.mode >= 2)
gpsdata->status = STATUS_FIX;
else
gpsdata->status = STATUS_NO_FIX;
gpsdata->set = STATUS_SET;
}
return (int)sizeof(struct gps_data_t);
}
}
/*@ +compdestroy */
}
void gps_shm_close(struct gps_data_t *gpsdata)
{
if (PRIVATE(gpsdata)->shmseg != NULL)
(void)shmdt((const void *)PRIVATE(gpsdata)->shmseg);
}
int gps_shm_mainloop(struct gps_data_t *gpsdata, int timeout UNUSED,
void (*hook)(struct gps_data_t *gpsdata))
/* run a shm main loop with a specified handler */
{
for (;;) {
if (!gps_shm_waiting(gpsdata, timeout)) {
return -1;
} else {
int status = gps_shm_read(gpsdata);
if (status == -1)
return -1;
if (status > 0)
(*hook)(gpsdata);
}
}
//return 0;
}
#endif /* SHM_EXPORT_ENABLE */
/* end */
|
