[Linux] linux使用共享内存通信的进程同步退出问题

struct shmid_ds {
struct ipc_perm shm_perm; /* Ownership and permissions */
size_t shm_segsz; /* Size of segment (bytes) */
time_t shm_atime; /* Last attach time */
time_t shm_dtime; /* Last detach time */
time_t shm_ctime; /* Last change time */
pid_t shm_cpid; /* PID of creator */
pid_t shm_lpid; /* PID of last shmat(2)/shmdt(2) */
shmatt_t shm_nattch; /* No. of current attaches */
...
};

/* shm_open - open a shared memory file */</p> <p>/* Copyright 2002, Red Hat Inc. */</p> <p>#include <sys/types.h>
#include <sys/mman.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <limits.h></p> <p>int
shm_open (const char *name, int oflag, mode_t mode)
{
int fd;
char shm_name[PATH_MAX+20] = "/dev/shm/";</p> <p> /* skip opening slash */
if (*name == '/')
++name;</p> <p> /* create special shared memory file name and leave enough space to
cause a path/name error if name is too long */
strlcpy (shm_name + 9, name, PATH_MAX + 10);</p> <p> fd = open (shm_name, oflag, mode);</p> <p> if (fd != -1)
{
/* once open we must add FD_CLOEXEC flag to file descriptor */
int flags = fcntl (fd, F_GETFD, 0);</p> <p> if (flags >= 0)
{
flags |= FD_CLOEXEC;
flags = fcntl (fd, F_SETFD, flags);
}</p> <p> /* on failure, just close file and give up */
if (flags == -1)
{
close (fd);
fd = -1;
}
}</p> <p> return fd;
}

/* shm_unlink - remove a shared memory file */</p> <p>/* Copyright 2002, Red Hat Inc. */</p> <p>#include <sys/types.h>
#include <sys/mman.h>
#include <unistd.h>
#include <string.h>
#include <limits.h></p> <p>int
shm_unlink (const char *name)
{
int rc;
char shm_name[PATH_MAX+20] = "/dev/shm/";</p> <p> /* skip opening slash */
if (*name == '/')
++name;</p> <p> /* create special shared memory file name and leave enough space to
cause a path/name error if name is too long */
strlcpy (shm_name + 9, name, PATH_MAX + 10);</p> <p> rc = unlink (shm_name);</p> <p> return rc;
}

xzc@xzc-HP-ProBook-4446s:/dev/shm$ stat abc
文件："abc"
大小：4 块：8 IO 块：4096 普通文件
设备：15h/21d Inode：5743159 硬链接：1
权限：(0664/-rw-rw-r--) Uid：( 1000/ xzc) Gid：( 1000/ xzc)
最近访问：2015-01-25 21:27:00.961053098 +0800
最近更改：2015-01-25 21:27:00.961053098 +0800
最近改动：2015-01-25 21:27:00.961053098 +0800
创建时间：-
xzc@xzc-HP-ProBook-4446s:/dev/shm$