所以我一直在努力学习更多关于共享内存的知识。我正在我的主人中创建一个共享内存结构并 fork child 。然后每个 child 都使用 execv 创建一个新进程。当我尝试从新进程更改共享内存的值时,父进程看不到该更改。我也期待 parent 与 child 交错执行。例如
Child 1 exec
parent
child 2 exec
parent
child 3 exec
parent
但是我得到了
child 1 exec
child 2 exec
child 3 exec
parent
parent
parent
这是我的代码
模拟.c
# include <unistd.h>
# include <sys/types.h>
# include <sys/stat.h>
# include <fcntl.h>
# include <time.h>
# include <stdlib.h>
# include <dirent.h>
# include <stdio.h>
# include <string.h>
# include <getopt.h>
# include <stdbool.h>
# include <ctype.h>
# include <sys/wait.h>
# include <signal.h>
# include <sys/mman.h>
# include <sys/time.h>
# include <stdint.h>
# include <fcntl.h>
# include <sys/shm.h>
struct sharedregion{
volatile int seconds;
volatile int sharedmsg;
};
struct sharedregion *mystruct;
void spawnchild()
{
int fd = shm_open("sharedmemory", O_CREAT | O_RDWR, S_IRUSR | S_IWUSR | S_IRWXG | S_IRWXU);
if (fd == -1)
perror("Error in opening");
if (ftruncate(fd, sizeof(struct sharedregion)) == -1)
perror("Unable to truncate");
mystruct = mmap(NULL, sizeof(struct sharedregion),PROT_READ | PROT_WRITE, MAP_SHARED| MAP_ANONYMOUS, fd, 0);
if (mystruct == MAP_FAILED)
perror("mapping failed");
mystruct->seconds=0;
mystruct->sharedmsg=0;
int i;
for(i=0;i<4;i++)
{
pid_t pID = fork();
if (pID == 0)
{
static char *args[]={"./child",NULL};
execv(args[0], args);
perror("failed to execv");
exit(EXIT_FAILURE);
}
else if (pID < 0) // failed to fork
{
perror(" Failed to fork:");
exit(EXIT_FAILURE);
}
else if(pID>0)
{
printf("\nfrom parent= %d",mystruct->sharedmsg);
mystruct->seconds=mystruct->seconds+1;
if(mystruct->seconds==1000000000)
{
mystruct->seconds=1;
}
}
}
}
int main(int argc, char **argv)
{
spawnchild();
}
child.c
# include <unistd.h>
# include <sys/types.h>
# include <sys/stat.h>
# include <fcntl.h>
# include <time.h>
# include <stdlib.h>
# include <dirent.h>
# include <stdio.h>
# include <string.h>
# include <getopt.h>
# include <stdbool.h>
# include <ctype.h>
# include <sys/wait.h>
# include <signal.h>
# include <sys/mman.h>
# include <sys/time.h>
# include <stdint.h>
# include <fcntl.h>
# include <sys/shm.h>
struct sharedregion{
volatile int seconds;
volatile int sharedmsg;
};
struct sharedregion *mystruct;
int main(int argc, char **argv)
{
int memFd = shm_open("sharedmemory", O_RDWR, S_IRUSR | S_IWUSR | S_IRWXG | S_IRWXU);
if (memFd == -1)
{
perror("Can't open file");
return 1;
}
mystruct = mmap(NULL, sizeof (struct sharedregion), PROT_READ | PROT_WRITE, MAP_SHARED| MAP_ANONYMOUS, memFd, 0);
printf("\nhello from exec");
mystruct->sharedmsg=8;
printf("buffer %d",mystruct->sharedmsg);
return 0;
}
我的输出
hello from execbuffer 8
hello from execbuffer 8
hello from execbuffer 8
hello from execbuffer 8
hello from execbuffer 8
from parent= 0
from parent= 0
from parent= 0
from parent= 0
from parent= 0
最佳答案
移除标志 MAP_ANONYMOUS
根据手册:
MAP_ANONYMOUS [...] The fd argument is ignored;
因此它会忽略你的共享内存
关于c - 共享内存不更新,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58223001/