c - 使用 ipcrm 删除共享内存 linux

Question

我正在使用共享内存在 C 上编写一个简单的应用程序，但我无法再运行它，因为它说:

shmat:无法分配内存

我正在使用 this脚本来释放我的内存，但似乎不起作用。

这是我的流程截图:

这是应用程序代码:

/* Shared Memory IPC creates a mamory space and send contendt to it while the other process can read from it.
Our implementation works like this:
    1. First run the application by passing as a argument the value you want to send to the shared memory. Example: ./ipc_sharedmem.o 4
    2. Run the appliation again to read from the shared memory (which is a new process, of course) wihout sending any arguments. Exmaple: ./ipc_sharedmem.o
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#define SHM_SIZE 1024  /* make it a 1K shared memory segment */

int main(int argc, char *argv[])
{
    key_t key;
    int shared_mem_mid;
    char *data;

    struct timeval t1, t2, t3, t4;

    if (argc > 2) {
        fprintf(stderr, "usage: shmdemo [data_to_write]\n");
        exit(1);
    }

    /* make the key: */
    if ((key = ftok("mach.c", 'R')) == -1) {
        perror("ftok");
        exit(1);
    }

    /* connect to (and possibly create) the segment: */
    if ((shared_mem_mid = shmget(key, SHM_SIZE, 0644 | IPC_CREAT)) == -1) {
        perror("shmget");
        exit(1);
    }

    /* attach to the segment to get a pointer to it: */
    gettimeofday(&t1, NULL);
    data = (char *) shmat(shared_mem_mid, (void *)0, 0);
    gettimeofday(&t2, NULL);
    if (data == (char *)(-1)) {
        perror("shmat");
        exit(1);
    }

    printf("Time to read the message from sharem memory: %g \n", (t2.tv_sec + t2.tv_usec/1000000.0)-(t1.tv_sec + t1.tv_usec/1000000.0));

    /* read or modify the segment, based on the command line: */
    if (argc == 2) {
        printf("writing to segment: \"%s\"\n", argv[1]);
        gettimeofday(&t3, NULL);
        strncpy(data, argv[1], SHM_SIZE);
        gettimeofday(&t4, NULL);
        printf("Time to send data to shared memory: %g \n", (t4.tv_sec + t4.tv_usec/1000000.0)-(t3.tv_sec + t3.tv_usec/1000000.0));
    } else{

        printf("segment contains: \"%s\"\n", data);
    }
    /* detach from the segment: */
    if (shmdt(data) == -1) {
        perror("shmdt");
        exit(1);
    }

    return 0;
}

有什么想法吗？

Answer 1

您的共享内存段被标记为已销毁，但仍附加有进程。

根据 source code ，nattach 列为 2，status 为“dest”，这意味着共享内存段有 2 个附件，一旦最后一个附加进程与段。

您需要让附加到段的进程调用 shmdt() 以从共享内存段分离，或者您需要终止这些进程。一旦你这样做，这些片段将被销毁。