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
|
// Copyright (C) Alan W. Irwin, 2016
// Copyright (C) Michael Kerrisk, 2016
//
// This program is free software. You may use, modify, and redistribute it
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 3 or (at your option) any
// later version. This program is distributed without any warranty. See
// the file COPYING.gpl-v3 for details.
// pshm_read.c
// Usage: pshm_read
// Read shared memory object created by pshm_write under unnamed
// semaphore control and dump the results to stdout.
#include <sys/types.h> // Type definitions used by many programs
#include <stdio.h> // Standard I/O functions
#include <stdlib.h> // Prototypes of commonly used library functions,
// plus EXIT_SUCCESS and EXIT_FAILURE constants
#include <unistd.h> // Prototypes for many system calls
#include <errno.h> // Declares errno and defines error constants
#include <string.h> // Commonly used string-handling functions
#include <semaphore.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include "pshm.h"
int
main(int argc, char *argv[])
{
int fd;
shmbuf *shmp;
int xfrs, bytes;
if (argc != 1)
{
fprintf(stderr, "%s should have no arguments because it only writes output to stdout\n", argv[0]);
exit(EXIT_FAILURE);
}
// Open existing shared object already created by pshm_write.
fd = shm_open(SHM_PATH, O_RDWR, 0);
if (fd == -1)
{
fprintf(stderr, "shm-open\n");
exit(EXIT_FAILURE);
}
shmp = mmap(NULL, sizeof(shmbuf), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (shmp == MAP_FAILED)
{
fprintf(stderr, "mmap\n");
exit(EXIT_FAILURE);
}
// 'fd' is no longer needed
if (close(fd) == -1)
{
fprintf(stderr, "close\n");
exit(EXIT_FAILURE);
}
for (xfrs = 0, bytes = 0; ; xfrs++, bytes += shmp->cnt)
{
// Wait for our turn
if(sem_wait(&shmp->rsem) == -1)
{
fprintf(stderr, "sem_wait\n");
exit(EXIT_FAILURE);
}
// pshm_write encountered an EOF.
if(shmp->cnt == 0)
break;
write(STDOUT_FILENO, shmp->buf, shmp->cnt);
// Give pshm_write a turn
if(sem_post(&shmp->wsem) == -1)
{
fprintf(stderr, "sem_post\n");
exit(EXIT_FAILURE);
}
}
// Let pshm_write know we are finished.
if(sem_post(&shmp->wsem) == -1)
{
fprintf(stderr, "sem_post\n");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
|
