Main code — shm-master.c
#include "posixver.h"
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <unistd.h>
#include "so-stderr.h"
enum { DEFAULT_SHM_SIZE = 65536 };
enum { DEFAULT_FTOK_ID = 0 };
static const char default_filename[] = "/etc/passwd";
static const char usestr[] = "[-adx][-f file][-s size][-i id]";
static const char optstr[] = "adf:s:x";
int main(int argc, char **argv)
{
int aflag = 0;
int xflag = 0;
int dflag = 0;
int id = DEFAULT_FTOK_ID;
size_t size = DEFAULT_SHM_SIZE;
const char *file = default_filename;
int opt;
err_setarg0(argv[0]);
while ((opt = getopt(argc, argv, optstr)) != -1)
{
switch (opt)
{
case 'a':
aflag = 1;
break;
case 'd':
dflag = 1;
break;
case 'f':
file = optarg;
break;
case 'i':
id = atoi(optarg);
break;
case 's':
size = strtoull(optarg, 0, 0);
if (size == 0)
err_error("Invalid size (%s) evaluates to zero\n", optarg);
break;
case 'x':
xflag = 1;
break;
default:
err_usage(usestr);
}
}
if (aflag + dflag + xflag > 1)
err_error("%d of 3 mutually exclusive options -a, -d and -x specified\n", aflag + dflag + xflag);
printf("ID: %d, File: %s\n", id, file);
key_t key = ftok(file, id);
printf("Key: 0x%.8" PRIX64 "\n", (uint64_t)key);
int shmflg = S_IRUSR | S_IWUSR;
if (!aflag && !dflag)
shmflg |= IPC_CREAT;
if (xflag)
shmflg |= IPC_EXCL;
int shmid = shmget(key, size, shmflg);
if (shmid < 0)
err_syserr("Failed to get shared memory ID: ");
printf("ShmID: %d\n", shmid);
if (dflag)
{
struct shmid_ds buf;
int rc = shmctl(shmid, IPC_RMID, &buf);
if (rc < 0)
err_syserr("Failed to delete shared memory: ");
printf("Shared memory removed\n");
}
else
{
void *space = shmat(shmid, 0, 0);
if (space == (void *)-1)
err_syserr("Failed to attach to shared memory: ");
printf("Shared memory allocated at 0x%" PRIXPTR "\n", (uintptr_t)space);
memset(space, '\0', size);
int rc = shmdt(space);
if (rc != 0)
err_syserr("Failed to detach from shared memory: ");
printf("Detached from shared memory\n");
}
return 0;
}
Library code — so-stderr.h
#ifndef SO_STDERR_H_INCLUDED
#define SO_STDERR_H_INCLUDED
extern void err_setarg0(const char *arg0);
extern void err_error(const char *fmt, ...);
extern void err_syserr(const char *fmt, ...);
#endif
Library code — so-stderr.c
#include "so-stderr.h"
#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static const char *argv0 = "**undefined**";
void err_setarg0(const char *arg0)
{
argv0 = arg0;
}
void err_error(const char *fmt, ...)
{
fprintf(stderr, "%s: ", argv0);
va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
exit(EXIT_FAILURE);
}
void err_syserr(const char *fmt, ...)
{
int errnum = errno;
fprintf(stderr, "%s: ", argv0);
va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
if (errnum != 0)
fprintf(stderr, "(%d: %s)", errnum, strerror(errnum));
putc('\n', stderr);
exit(EXIT_FAILURE);
}
配置头文件 — posixver.h
在许多系统上,您可以将更高的版本号调整为700(适用于POSIX 2008/2013),但即使在10.10.3 Yosemite下,也不建议在Mac OS X上这样做。
#ifndef JLSS_ID_POSIXVER_H
#define JLSS_ID_POSIXVER_H
#if !defined(_XOPEN_SOURCE) && !defined(_POSIX_C_SOURCE)
#if __STDC_VERSION__ >= 199901L
#define _XOPEN_SOURCE 600
#else
#define _XOPEN_SOURCE 500
#endif
#endif
在所有情况下,“真实”的代码包括(少量)注释和其他说明。生产环境中的stderr.h
和stderr.c
比所示的最小版本更复杂,但对于许多目的而言,所示内容与生产版本相当。
运行示例
$ ./shm-master -H
./shm-master: invalid option -- 'H'
Usage: ./shm-master [-adx][-f file][-s size][-i id]
$ ./shm-master -ax
./shm-master: 2 of 3 mutually exclusive options -a, -d and -x specified
$ ./shm-master -dx
./shm-master: 2 of 3 mutually exclusive options -a, -d and -x specified
$ ./shm-master -da
./shm-master: 2 of 3 mutually exclusive options -a, -d and -x specified
$ ./shm-master -dax
./shm-master: 3 of 3 mutually exclusive options -a, -d and -x specified
$ ipcs -m | grep -v '^0x00000000 '
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x620010f7 0 root 660 557920 4
0x63002725 32769 root 666 82164 3
$ ./shm-master -x
ID: 0, File: /etc/passwd
Key: 0x0000009F
ShmID: 44793901
Shared memory allocated at 0x7F29AC43A000
Detached from shared memory
$ ipcs -m | grep -v '^0x00000000 '
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x620010f7 0 root 660 557920 4
0x63002725 32769 root 666 82164 3
0x0000009f 44793901 jleffler 600 65536 0
$ ./shm-master -d
ID: 0, File: /etc/passwd
Key: 0x0000009F
ShmID: 44793901
Shared memory removed
$ ipcs -m
$ grep -v '^0x00000000 '
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x620010f7 0 root 660 557920 4
0x63002725 32769 root 666 82164 3
$ ./shm-master -f /home/jleffler/soq/shm-master -a
./shm-master: Failed to get shared memory ID: (2: No such file or directory)
ID: 0, File: /home/jleffler/soq/shm-master
Key: 0x00010FB9
$ ./shm-master -f /home/jleffler/soq/shm-master -d
./shm-master: Failed to get shared memory ID: (2: No such file or directory)
ID: 0, File: /home/jleffler/soq/shm-master
Key: 0x00010FB9
$ ./shm-master -f /home/jleffler/soq/shm-master -x
ID: 0, File: /home/jleffler/soq/shm-master
Key: 0x00010FB9
ShmID: 44826669
Shared memory allocated at 0x7FA1488CA000
Detached from shared memory
$ ./shm-master -f /home/jleffler/soq/shm-master -d
ID: 0, File: /home/jleffler/soq/shm-master
Key: 0x00010FB9
ShmID: 44826669
Shared memory removed
$ ./shm-master -f /home/jleffler/soq/shm-master -x
ID: 0, File: /home/jleffler/soq/shm-master
Key: 0x00010FB9
ShmID: 44859437
Shared memory allocated at 0x7F93005EC000
Detached from shared memory
$ shmid=$(./shm-master -f /home/jleffler/soq/shm-master -a sed -n '/ShmID: /s///p')
$ ipcs -m -i $shmid
Shared memory Segment shmid=44859437
uid=199484 gid=5000 cuid=199484 cgid=5000
mode=0600 access_perms=0600
bytes=65536 lpid=31202 cpid=31200 nattch=0
att_time=Fri Apr 17 11:37:06 2015
det_time=Fri Apr 17 11:37:06 2015
change_time=Fri Apr 17 11:37:06 2015
$ ./shm-master -f /home/jleffler/soq/shm-master -d
ID: 0, File: /home/jleffler/soq/shm-master
Key: 0x00010FB9
ShmID: 44859437
Shared memory removed
$
顺便提一下,
ipcs
选项
-i id
是Linux在
ipcs
的POSIX规范上做的扩展,在其他操作系统比如Mac OS X(BSD)上不可用。最接近的等效方法是
ipcs -m -a | grep "$shmid"
,但这并不完美。
grep -v '^0x00000000 '
操作排除了私有共享内存段(在我测试的机器上有很多)。
malloc()
及其相关函数的返回值进行强制转换。 - Sourav Ghoshwhile (!feof(file))
is always wrong。这不是正确的做法:while (fscanf(file, "%d", &i) == 1) insertArray(&numbers, i);
才是正确的方法。 - Jonathan Leffler/dev/shm
上进行fread
和fwrite
操作。 - David Ranieriftok()
函数要求两个进程就文件名达成一致。或者父进程可以向执行后的子进程传递一个字符串来标识共享内存段(作为段ID、文件名等)。利用shmget()
、shmat()
、shmdt()
、shmctl()
函数实现。 - Jonathan Leffler