Linux程序设计：进程通信

 

日期：忘了。

关键词：Linux程序设计；System-V；进程通信；共享内存；消息队列。

一、共享内存

 

1.1 基本知识

（待补充）

 

1.2 代码

一个基于share memory实现的客户-服务模型。

• shm_comm.h

#define TEXT_SZ 2048

struct shared_use_st

{

    int written_by_you;

    char some_text[TEXT_SZ];

};

typedef
struct shared_use_st shared_use_st;

• shm1.c

 

#include <unistd.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/shm.h>

#include "shm_com.h"

 

int main()

{

    int running = 1;

    void *shm_ptr = NULL;

    struct shared_use_st *shared_stuff;

    int shmid;

 

    srand((unsigned
int)getpid());

 

    shmid = shmget((key_t)1234, sizeof(shared_use_st), 0666 | IPC_CREAT);

    printf("shmid = %x\n", shmid);

    if (shmid == -1)

    {

        fprintf(stderr, "shmget fail\n");

        exit(EXIT_FAILURE);

    }

    shm_ptr = shmat(shmid, NULL, 0);

    //该值应该是shm在当前进程空间中的虚拟地址，而不是shm真实的物理地址

    //所以shm1和shm2的返回值不一样

 

    if (shm_ptr == (void *)-1)

    {

        fprintf(stderr, "shmat failed\n");

        exit(EXIT_FAILURE);

    }

 

    printf("Memory attached at %p\n", shm_ptr);

 

    shared_stuff = (struct shared_use_st *)shm_ptr;

    shared_stuff->written_by_you = 0;

    while (running)

    {

        if (shared_stuff->written_by_you)

        {

            printf("You wrote %s\n", shared_stuff->some_text);

            sleep(5);

            shared_stuff->written_by_you = 0;

            if (strncmp(shared_stuff->some_text, "end", 3) == 0)

            {

                running = 0;

            }

        }

    }

 

    if(shmdt(shm_ptr) == -1)

    {

        fprintf(stderr, "shmdt failed\n");

        exit(EXIT_FAILURE);

    }

 

    if(shmctl(shmid, IPC_RMID, NULL) == -1)

    {

        fprintf(stderr, "shmctl(IPC_RMID) failed\n");

        exit(EXIT_FAILURE);

    }

    exit(EXIT_SUCCESS);

}

 

• shm2.c

 

#include <unistd.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/shm.h>

#include "shm_com.h"

 

int main()

{

    int running = 1;

    void *shm_ptr = NULL;

    struct shared_use_st *share_stuff;

    char buff[TEXT_SZ];

    int shmid;

 

    shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666|IPC_CREAT);

    printf("shmid = %x\n", shmid);

    if(shmid == -1)

    {

        fprintf(stderr, "shmget failed\n");

        exit(EXIT_FAILURE);

    }

 

    shm_ptr = shmat(shmid, NULL, 0);

    if(shm_ptr == (void *)-1)

    {

        fprintf(stderr, "shmat failed\n");

        exit(EXIT_FAILURE);

    }

    printf("Memory attached at %p\n", shm_ptr);

 

    share_stuff = (struct shared_use_st*)shm_ptr;

 

    while(running)

    {

        if(share_stuff->written_by_you == 1)

        {

            sleep(1);

            printf("waiting for client\n");

        }

        printf("Enter texts:");

        fgets(buff, TEXT_SZ, stdin);

        strncpy(share_stuff->some_text, buff, TEXT_SZ);

        share_stuff->written_by_you = 1;

        
 

        if(strncmp(share_stuff->some_text, "end", 3) == 0)

        {

            running = 0;

        }

    }

 

    if(shmdt(shm_ptr) == -1)

    {

        fprintf(stderr, "shmdt failed\n");

        exit(EXIT_FAILURE);

    }

    exit(EXIT_SUCCESS);

 

}

• 运行结果

  

二、消息队列

2.1 基本知识

待补充。

2.2 代码

• msg1.c

 

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <errno.h>

#include <unistd.h>

 

#include <sys/msg.h>

struct msg_t

{

    long
int msg_type;

    char content[BUFSIZ];

};

 

int main()

{

    int running = 1;

    int msgid;

    long
表示获取队列第一个可用消息

    struct msg_t msg;

 

    msgid = msgget((key_t)1234, 0666 | IPC_CREAT);

    printf("msgid = %d\n", msgid);

    if (msgid == -1)

    {

        fprintf(stderr, "msgget failed\n");

        exit(EXIT_FAILURE);

    }

 

    while (running)

    {

        if (msgrcv(msgid, (void *)&msg, BUFSIZ, msg_to_receive, 0) == -1)

        {

            fprintf(stderr, "msgrcv failde\n");

            exit(EXIT_FAILURE);

        }

        printf("You wrote %s", msg.content);

        if(strncmp(msg.content, "end", 3) == 0)

            running = 0;

    }

    if (msgctl(msgid, IPC_RMID, 0) == -1)

    {

        fprintf(stderr, "msgcntl failed\n");

        exit(EXIT_FAILURE);

    }

    exit(EXIT_SUCCESS);

 

}

 

 

• msg2.c

 

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <errno.h>

#include <unistd.h>

#include <sys/msg.h>

#define MAX_TEXT 512

struct msg_t

{

    long
int msg_type;

    char content[BUFSIZ];

};

 

int main()

{

    int running = 1;

    struct msg_t msg;

    int msgid;

    char buffer[BUFSIZ];

 

    msgid = msgget((key_t)1234, 0666 | IPC_CREAT);

    printf("msgid = %d\n", msgid);

 

    if (msgid == -1)

    {

        fprintf(stderr, "msgget failed\n");

        exit(EXIT_FAILURE);

    }

 

    while (running)

    {

        printf("Enter texts:");

        fgets(buffer, BUFSIZ, stdin);

        msg.msg_type = 1;

        strcpy(msg.content, buffer);

 

        if(msgsnd(msgid, (void *)&msg, BUFSIZ, 0) == -1)

        {

            fprintf(stderr, "msgsnd failed\n");

            exit(EXIT_FAILURE);

        }

        if(strncmp(msg.content, "end", 3) == 0)

        {

            running = 0;

        }

    }

 

    exit(EXIT_SUCCESS);

}

 

三、信号量

3.1 基本知识

待补充。

3.2 代码

• semun.h

 

#if defined(__GNU_LIBRARY__) &&
!defined(_SEM_SEMUN_UNDEFINED)

    /* union semun is defined by including <sys/sem.h> */

#else

    /* according to X/OPEN we have to define it ourselves */

    union semun {

        int val; /* value for SETVAL */

        struct semid_ds *buf; /* buffer for IPC_STAT, IPC_SET */

        unsigned
short
int *array; /* array for GETALL, SETALL */

        struct seminfo *__buf; /* buffer for IPC_INFO */

    };

#endif

 

 

• sema.c

#include <stdio.h>

#include <unistd.h>

#include <stdlib.h>

#include <sys/sem.h>

#include "semun.h"

 

static
int sem_id;

static
int set_semvalue()

{

    union semun sem_union;

    sem_union.val = 1;

    if (semctl(sem_id, 0, SETVAL, sem_union) == -1)

        return
0;

    return
1;

}

static
void del_semvalue()

{

    union semun sem_union;

    if (semctl(sem_id, 0, IPC_RMID, sem_union) == -1)

        fprintf(stderr, "Fail to delete semaphore\n");

}

static
int sema_p()

{

    struct sembuf sem_b;

    sem_b.sem_num = 0;//信号量编号，除非是一组信号量，否则0

    sem_b.sem_op = -1;//-1操作

    sem_b.sem_flg = SEM_UNDO;//与操作系统对信号量的操作相关，一般是UNDO

    if (semop(sem_id, &sem_b, 1) == -1)

    {

        fprintf(stderr, "sema_p failed\n");

        return
0;

    }

    return
1;

}

static
int sema_v()

{

    struct sembuf sem_b;

    sem_b.sem_num = 0;

    sem_b.sem_op = 1;

    sem_b.sem_flg = SEM_UNDO;

    if (semop(sem_id, &sem_b, 1) == -1)

    {

        fprintf(stderr, "sema_v failed\n");

        return
0;

    }

    return
1;

}

 

int main(int argc, char *argv[])

{

    int i;

    int pause_time;

    char op_char = 'O';

    srand((unsigned
int)getpid());

    sem_id = semget((key_t)1234, 1, 0666 | IPC_CREAT);

    if (argc > 1)

    {

        if(set_semvalue() == 0)

        {

            fprintf(stderr, "init fail\n");

            exit(EXIT_FAILURE);

        }

        op_char = 'X';

        sleep(2);

    }

 

    for (i = 0; i < 10; i++)

    {

        if (sema_p() == 0)

            exit(EXIT_FAILURE);

        printf("%c", op_char);

        fflush(stdout);

 

        pause_time = rand() % 3;

        sleep(pause_time);

        printf("%c", op_char);

        fflush(stdout);

 

        if (!sema_v())

            exit(EXIT_FAILURE);

        pause_time = rand() % 2;

        sleep(pause_time);

    }

    printf("\n%d - finished\n", getpid());

    if (argc > 1)

    {

        sleep(10);

        del_semvalue();

    }

    exit(EXIT_SUCCESS);

}