linux操作系統編程——共享內存的讀寫（採用信號機制進行同步互斥）

程序要求：

   創建一個寫端和一個讀端，寫端寫入數據後讀端纔開始讀，讀端讀完數據後，寫端纔可以開始寫，這樣的同步採用信號機制實現，並且寫端與讀端打開順序不同也能實現功能；

程序如下：

（1）、write.c（寫端）

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

typedef struct
{
    pid_t pid;
    char buf[1024];
}memory;

void write_func(int sig_no)
{
    return ;
}

int main(int argc, const char *argv[])
{
    key_t key;
    memory *p = NULL;
    int shmid;
    pid_t pid;
    int create_flag = 0;

    signal(SIGUSR1, write_func);

    if ((key = ftok(".", 'a')) < 0)
    {
        perror("failed to get key");
        exit(-1);
    }

    if ((shmid = shmget(key, sizeof(memory), 0666 | IPC_CREAT | IPC_EXCL)) < 0)
    {
        if (errno == EEXIST)
        {       
            if ((shmid = shmget(key, sizeof(memory), 0666)) < 0)
            {
                perror("failed to shmget memory");
                exit(-1);
            }

            if ((p = shmat(shmid, NULL, 0)) == (void *)(-1))
            {
                perror("failed to shmat share memory");
                exit(-1);
            }

            pid = p->pid;
            p->pid = getpid();
            kill(pid, SIGUSR1);
        }
        else
        {
            perror("failed to shmget");
            exit(-1);
        }
    }
    else
    {
        create_flag = 1;

        if ((p = shmat(shmid, NULL, 0)) == (void *)(-1))
        {
            perror("failed to shmat memory");
            exit(-1);
        }

        p->pid = getpid();
        pause();
        pid = p->pid;
    }

    while(1)
    {
        printf(">");
        fgets(p->buf, sizeof(p->buf), stdin);
        p->buf[strlen(p->buf) - 1] = 0;

        kill(pid, SIGUSR1);

        if (strncmp(p->buf, "quit", 4) == 0)
            break;
    }

    if (create_flag == 1)
    {
        if (shmdt(p) < 0)
        {
            perror("failed to shmdt memory");
            exit(-1);
        }

        if (shmctl(shmid, IPC_RMID, NULL) == -1)
        {   
            perror("failed to delete share memory");
            exit(-1);
        }
    }

    return 0;
}

（2）、read.c（讀端）

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

typedef struct
{
    pid_t pid;
    char buf[1024];
}memory;

void read_func(int sig_no)
{
    return ;
}

int main(int argc, const char *argv[])
{
    int pid;
    key_t key;
    int shmid;
    memory *p = NULL;
    int create_flag = 0;

    signal(SIGUSR1, read_func);

    if ((key = ftok(".", 'a')) < 0)
    {
        perror("failed to get key");
        exit(-1);
    }

    if ((shmid = shmget(key, sizeof(memory), 0666 | IPC_CREAT | IPC_EXCL)) < 0)
    {
        if (errno == EEXIST)
        {
            if ((shmid = shmget(key, sizeof(memory), 0666)) < 0)
            {
                perror("failed to create share memory");
                exit(-1);
            }
            
            if ((p = shmat(shmid, NULL, 0)) == (void *)(-1))
            {
                perror("failed to shmat");
                exit(-1);
            }

            pid = p->pid;
            p->pid = getpid();
            kill(pid , SIGUSR1);
        }
        else
        {
            perror("failed to shmget");
            exit(-1);
        }
    }
    else
    {
        create_flag = 1;

        if ((p = shmat(shmid, NULL, 0)) == (void *)(-1))
        {
            perror("failed to shmat");
            exit(-1);
        }

        p->pid = getpid();
        pause();
        pid = p->pid;
    }
    
    while(1)
    {
        pause();

        if (strncmp(p->buf, "quit", 4) == 0)
            break;

        printf("recv: %s\n", p->buf);

    }

    if (create_flag == 1)
    {
        if (shmdt(p) < 0)
        {
            perror("failed to shmdt");
            exit(-1);
        }

        if (shmctl(shmid, IPC_RMID, NULL) == -1)
        {
            perror("failed to delete share memory");
            exit(-1);
        }
    }

    return 0;
}