进程间通信：共享内存2

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#ifndef T_DESC
#define T_DESC(x, y)   (y)
#endif

#define TEXT_SZ 256  
  
struct shared_use_st  
{  
    int  written;//作为一个标志，非0：表示可读，0表示可写  
    char text[TEXT_SZ];//记录写入和读取的文本  
};  


#if T_DESC("TU1", 1)

int tu1_proc()
{
    int running = 1;//程序是否继续运行的标志
    void *shm = NULL;//分配的共享内存的原始首地址
    struct shared_use_st *shared;//指向shm
    int shmid;//共享内存标识符
    
    //创建共享内存
    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666|IPC_CREAT);
    if(shmid == -1)
    {
        fprintf(stderr, "shmget failed\n");
        exit(EXIT_FAILURE);
    }
    
    //将共享内存连接到当前进程的地址空间
    shm = shmat(shmid, 0, 0);
    if(shm == (void*)-1)
    {
        fprintf(stderr, "shmat failed\n");
        exit(EXIT_FAILURE);
    }
    printf("\nMemory attached at 0x%x\n", (int)shm);
    
    //设置共享内存
    shared = (struct shared_use_st*)shm;
    
    shared->written = 0;
    while(running)//读取共享内存中的数据
    {
        if(shared->written == 0) 
            sleep(1); //没有数据可读取
        else
        {
            printf("read data: %s", shared->text);
            sleep(1);
            shared->written = 0;
            
            //输入了end，退出循环（程序）
            if(strncmp(shared->text, "end", 3) == 0)
                running = 0;
        }
    }
    
    //把共享内存从当前进程中分离
    if(shmdt(shm) == -1)
    {
        fprintf(stderr, "shmdt failed\n");
        exit(EXIT_FAILURE);
    }
    
    //删除共享内存
    if(shmctl(shmid, 0, 0) == -1)
    {
        fprintf(stderr, "shmctl(IPC_RMID) failed\n");
        exit(EXIT_FAILURE);
    }
    
    exit(EXIT_SUCCESS);
}

int tu2_proc()
{
    int running = 1;
    void *shm = NULL;
    struct shared_use_st *shared = NULL;
    char buffer[BUFSIZ + 1];//用于保存输入的文本
    int shmid;
    
    //创建共享内存
    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666|IPC_CREAT);
    if(shmid == -1)
    {
        fprintf(stderr, "shmget failed\n");
        exit(EXIT_FAILURE);
    }
    
    //将共享内存连接到当前进程的地址空间
    shm = shmat(shmid, (void*)0, 0);
    if(shm == (void*)-1)
    {
        fprintf(stderr, "shmat failed\n");
        exit(EXIT_FAILURE);
    }
    printf("Memory attached at 0x%x\n", (int)shm);
    
    //设置共享内存
    shared = (struct shared_use_st*)shm;
    while(running)//向共享内存中写数据
    {
        //数据还没有被读取，则等待数据被读取,不能向共享内存中写入文本
        while(shared->written == 1)
        {
            sleep(1);
            printf("Waiting...\n");
        }
        
        //向共享内存中写入数据
        printf("Enter some text: ");
        fgets(buffer, BUFSIZ, stdin);
        strncpy(shared->text, buffer, TEXT_SZ);
        
        //写完数据，设置written使共享内存段可读
        shared->written = 1;
        
        //输入了end，退出循环（程序）
        if(strncmp(buffer, "end", 3) == 0)
            running = 0;
    }
    
    //把共享内存从当前进程中分离
    if(shmdt(shm) == -1)
    {
        fprintf(stderr, "shmdt failed\n");
        exit(EXIT_FAILURE);
    }
    
    sleep(2);
    exit(EXIT_SUCCESS);
}

#endif

#if T_DESC("global", 1)
void usage()
{
    printf("\n Usage: <cmd> <tu> <p1> <...>");
    printf("\n   1 -- create task 1");
    printf("\n   2 -- create task 2");
    printf("\n");
}

int main(int argc, char **argv)
{
    int ret;
    
    if(argc < 2) {
        usage();
        return 0;
    }

    int tu = atoi(argv[1]);
    if (tu == 1) ret = tu1_proc();
    if (tu == 2) ret = tu2_proc();
    
    return ret;
}
#endif