Linux网络编程--进程间通信（一）

//管道的性质就是，一个进程的输出作为另一个进程的输入
//那么我们可以关闭一个进程读端使之作为输入端，
//另一个进程关闭写端，读取数据，接收数据作为管道输出端

//FIFO命名管道
//文件系统中，命名管道是特殊文件的方式存在的
//不同进程可以通过命名管道共享数据

//命名管道一直是阻塞方式的，且必须是显示的通过open建立连接到管道的通道
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>

#include<sys/types.h>

int main()
{
    int result = 1;
    int fd[2];
    pid_t pid;
    int *write_fd = &fd[1];        //写文件描述
    int *read_fd = &fd[0];        //读文件描述
    
    int nbytes;
    char str[] = "管道，你好\n";    
    char readBuffer[80];
    memset(readBuffer,0,sizeof(readBuffer));

    result = pipe(fd);        //创建管道
    if(-1==result)
    {
        printf("管道创建失败！\n");
        return -1;
    }
    
    pid = fork();            //进程创建分叉程序
    if(-1 == pid)
    {
        printf("fork失败");
        return -1;
    }

    if(0==pid)            //子进程关闭读端，写入字符
    {
        close(*read_fd);
        result = write(*write_fd,str,strlen(str));
        printf("写入%d个数据\n",result);
    }
    else                //父进程关闭写端，读取数据
    {
        close(*write_fd);
        nbytes = read(*read_fd,readBuffer,sizeof(readBuffer));
        printf("接收到%d个数据，内容为%s",nbytes,readBuffer);
    }
    return 0;
}

//file： msg.h
/* message buffer for msgsnd and msgrcv calls */
struct msgbuf {
    __kernel_long_t mtype;          /* type of message */
    char mtext[1];                  /* message text */
};

/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct msqid_ds {
    struct ipc_perm msg_perm;
    struct msg *msg_first;        /* first message on queue,unused  */
    struct msg *msg_last;        /* last message in queue,unused */
    __kernel_time_t msg_stime;    /* last msgsnd time */
    __kernel_time_t msg_rtime;    /* last msgrcv time */
    __kernel_time_t msg_ctime;    /* last change time */
    unsigned long  msg_lcbytes;    /* Reuse junk fields for 32 bit */
    unsigned long  msg_lqbytes;    /* ditto */
    unsigned short msg_cbytes;    /* current number of bytes on queue */
    unsigned short msg_qnum;    /* number of messages in queue */
    unsigned short msg_qbytes;    /* max number of bytes on queue */
    __kernel_ipc_pid_t msg_lspid;    /* pid of last msgsnd */
    __kernel_ipc_pid_t msg_lrpid;    /* last receive pid */
};

//filename
/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct ipc_perm
{
    __kernel_key_t    key;　　//函数msgget()使用的键值　　
    __kernel_uid_t    uid;　　//用户UID
    __kernel_gid_t    gid;　　//用户GID
    __kernel_uid_t    cuid;　　//创建者UID
    __kernel_gid_t    cgid;　　//创建者GID
    __kernel_mode_t    mode; 　　//权限
    unsigned short    seq;　　//序列号
};

//filename sys/sem.h
/* arg for semctl system calls. */
union semun {
    int val;            /* value for SETVAL */
    struct semid_ds *buf;    /* buffer for IPC_STAT & IPC_SET */
    unsigned short *array;    /* 数组结构 */
    struct seminfo *__buf;    /* 信号量内部结构 */
    void *__pad;
};

#include<stdio.h>
#include<unistd.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<sys/types.h>

typedef int sem_t;
union semun
{
    int val;
    struct semid_ds * buf;
    unsigned short *array;
}arg;

sem_t CreateSem(key_t key, int value)
{
    union semun sem;
    sem_t semid;
    sem.val = value;
    
    semid = semget(key,0,IPC_CREAT);
    if(-1 == semid)
    {
        printf("create semaphore error\n");
        return -1;
    }
    
    semctl(semid,0,SETVAL,sem);
    
    return semid;
}

int Sem_P(sem_t semid)
{
struct sembuf sops = {0,+1,IPC_NOWAIT};
return (semop(semid,&sops,1));
}

int Sem_V(sem_t semid)
{
    struct sembuf sops = {0,-1,IPC_NOWAIT};
    return (semop(semid,&sops,1));
}

void SetvalueSem(sem_t semid , int value)
{
    union semun sem;
    sem.val = value;
    semctl(semid,0,SETVAL,sem);
}

int GetvalueSem(sem_t semid)
{
    union semun sem;
    return semctl(semid,0,GETVAL,sem);
}

void DestroySem(sem_t semid)
{
    union semun sem;
    sem.val = 0;
    semctl(semid,0,IPC_RMID,sem);
}
int main()
{
    key_t key;
    int semid;
    char i;
    int value = 0;
    key = ftok("/ipc/sem",‘a‘);
    
    semid = CreateSem(key,100);
    for( i = 0;i <= 3;++i)
    {
        Sem_P(semid);
        Sem_V(semid);    
    }
    value = GetvalueSem(semid);    
    
    DestroySem(semid);    
    return 0;
}