UNIX 如果查询一个共享内存已经被IPCRM了

[pengxn]

先启动了一个进程，进程中连接了一个共享内存，并保存了SHM_id，
然后手工删除这块共享内存，使用IPCRM命令

请问如何在该进程中，根据命令查询这块内存已经申请删除了。通过shmctl似乎不行

[wqkjj]

if( msgget( Queue_Key, perms ) == -1 ) && errno == ENOENT )

[wqkjj]

汗，写成消息队列的了,再写一个
if( shmget(shmkey,size,shmflag) == -1 && errno == EEXIST )

[pengxn]

[Quote=引用 2 楼 wqkjj 的回复:]
汗，写成消息队列的了,再写一个
if( shmget(shmkey,size,shmflag) == -1 && errno == EEXIST )
[/Quote]

NO NO NO

[wqkjj]

[Quote=引用 3 楼 pengxn 的回复:]
引用 2 楼 wqkjj 的回复:
汗，写成消息队列的了,再写一个
if( shmget(shmkey,size,shmflag) == -1 && errno == EEXIST )


NO NO NO
[/Quote]

哦，EEXIST不能识别这种情况。
那就自己写一个函数也很简单:
popen("ipcs -m".....);
然后读输出结果，判断你的shmid或者shmkey是否存在。

[mymtom]

进程内可以用根据ipc_perm的mode成员SHM_DEST位进行判断

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#include <stdio.h>

int main(void)
{
    key_t key;
    int id;
    size_t size;
    void *addr;
    int ch;
    struct shmid_ds buf;
    unsigned int mode;

    key = ftok("shm.key", 1);
    size = 1024;
    id = shmget(key, size, SHM_R | SHM_W | IPC_CREAT);
    addr =  shmat(id, NULL, 0);

    while ((ch = getchar()) != EOF) {
        shmctl(id, IPC_STAT, &buf);
        mode = buf.shm_perm.mode;
        (void)printf("%o\n", (unsigned short)mode);
#ifdef SHM_DEST
        if (SHM_DEST & mode)
            (void)printf("%s\n", "destroy segment when # attached = 0");
#endif
    }

    shmdt(addr);
    shmctl(id, IPC_RMID, NULL);

    return 0;
}

用ipcs -m命令进行检查，如果在MODE列有D标志，表示已被其他进程删除。

IPC status from /dev/mem as of Tue Jun 29 20:37:31 BEIST 2010
T        ID     KEY        MODE       OWNER    GROUP
Shared Memory:
m         0 0x580022ed --rw-rw-rw-     root   system
m   1048577 0x0d000553 --rw-rw----     root   system
m   1048578 0xffffffff --rw-rw----     root   system
m   1048579 0x78000004 --rw-rw-rw-     root   system
m         4 0x00001515 --rw-rw-rw-  hsh1985   member
m         5 0xffffffff --rw-rw-r-- friedric   member
m         6 0xffffffff --rw-rw-r-- friedric   member
m         7 0xffffffff --rw-rw-r-- friedric   member
m         8 0xffffffff --rw-rw-r-- friedric   member
m   7340042 0xff2b0a63 --rw-rw-r-- friedric   member
m        11 0xff2b0a60 --rw-rw-r-- friedric   member
m        12 0xff2b0a5f --rw-rw-r-- friedric   member
m        13 0xff2b0a61 --rw-rw-r-- friedric   member
m  15728655 0xff2b0491 --rw-rw-r-- friedric   member
m  23068688 0xffffffff D-rw-------   mymtom   member

MODE
(all) the facility access modes and flags. The mode consists of 11 characters that are interpreted as follows:

The first two characters can be the following:
R
If a process is waiting on a msgrcv system call.
S
If a process is waiting on a msgsnd system call.
D
If the associated shared memory segment has been removed. It disappears when the last process attached
to the segment detaches it.
C
If the associated shared memory segment is to be cleared when the first attach is run.
-
If the corresponding special flag is not set.