进程通信之共享内存篇

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

#define BUFFER_SIZE 2048

int main()
{
pid_t pid;
int shmid;
char* shm_addr;
char flag[] = "WROTE";
char buff[BUFFER_SIZE];

/* 创建共享内存 */
if((shmid = shmget(IPC_PRIVATE, BUFFER_SIZE, 0666)) < 0)
{
perror("shmget");
exit(1);
}
else
{
printf("Create share-memory: %d\n", shmid);
}

/* 显示共享内存情况 */
system("ipcs -m");

pid = fork();
if(pid == -1)
{
perror("fork");
exit(1);
}
else
if( pid == 0 )    /* 子进程处理 */
{
/* 映射共享内存 */
if((shm_addr = shmat(shmid, 0, 0)) == (void*)-1)
{
perror("Child: shmat");
exit(1);
}
else
{
printf("Child: Attach shared-memory: %p\n", shm_addr);
}
system("ipcs -m");

/* 通过检查在共享内存的头部是否是标志字符串WROTE来确认
父进程已经向共享内存写入有效数据 */
while( strncmp(shm_addr, flag, strlen(flag)) )
{
printf("Child: Wait for enable data...\n");
sleep(5);
}

/* 获取共享内存的有效数据并显示 */
strcpy(buff, shm_addr + strlen(flag));
printf("Child: Shared-memory : %s \n",buff);

/* 解除共享内存映射 */
if((shmdt(shm_addr)) < 0)
{
perror("shmdt");
exit(1);
}
else
{
printf("Child: Deattach shared-memory\n");
}
system("ipcs -m");

/* 删除共享内存 */
if(shmctl(shmid, IPC_RMID, NULL) == -1)
{
perror("Child: shmctl(IPC_RMID) \n");
exit(1);
}
else
{
printf("Delete shared-memory\n");
}

system("ipcs -m");
}
else    /* 父进程处理 */
{
/* 映射共享内存 */
if((shm_addr = shmat(shmid, 0, 0)) == (void*)-1)
{
perror("Parent: shmat");
exit(1);
}
else
{
printf("Parent: Attach shared-memory: %p\n", shm_addr);
}

sleep(1);
printf("\n Input some string: \n");
fgets(buff, BUFFER_SIZE, stdin);
strncpy(shm_addr + strlen(flag), buff, strlen(buff));
strncpy(shm_addr, flag, strlen(flag));

/* 解除共享内存映射 */
if((shmdt(shm_addr)) < 0)
{
perror("Parent: shmdt");
exit(1);
}
else
{
printf("Parent: Deattach shared-memory\n");
}
system("ipcs -m");

waitpid(pid, NULL, 0);
printf("Finished\n");
}
return 0;
}