Linux信号量同步共享内存实验.

简述

本文主要内容是自己对信号量和共享内存系统函数的整理,及简单使用,以方便以后可能再次使用的情况.也可以为比较熟悉信号量和共享内存的人方便的回忆使用方法. 

实验简述. 
1.本实验程序有两个进程,一个写,一个读. 
2.写进程不断向创建的共享内存写数据. 
3.读进程通过getchar()共享内存的最新数据. 
4.读写共享内存时通过信号量同步.

程序流程

信号量和共享内存的系统函数

信号量系统函数及接口

#include "sem.h" 
#include "debug.h" 

#define IPCKEY_PATH "/" 
#define SEM_NUMS 1 
#define SEM_OPS_NUM 1 
#define ACCESS_BIT 0666 

#define TAG "SemInterface" 

int sem_new(unsigned char projid, int init_val) 
{ 
    key_t key; 
    int semid; 
    union semun sem_union; 

    key = ftok(IPCKEY_PATH, projid); 
    if(key < 0) 
    { 
        LOG_E("ftok error: %s\n", strerror(errno)); 
        return SEM_FAILURE; 
    } 

    semid = semget(key, SEM_NUMS, ACCESS_BIT|IPC_CREAT|IPC_EXCL); 
    if(semid < 0) 
    { 
        if(errno == EEXIST) 
        { 
        LOG_E("sem exist: %s\n", strerror(errno)); 
        return SEM_EXIST; 
        } 
        LOG_E("create sme error: %s\n", strerror(errno)); 
        return SEM_FAILURE; 
    } 

    sem_union.val = init_val; 
    if((semctl(semid, 0, SETVAL, sem_union)) < 0) 
    { 
        LOG_E("set sem val error: %s\n", strerror(errno)); 
        return SEM_FAILURE; 
    } 

    return semid; 
} 


int sem_get(unsigned char proj_id) 
{ 
    key_t key; 
    int semid; 
    union semun sem_union; 

    key = ftok(IPCKEY_PATH, proj_id); 
    if(key < 0) 
    { 
        LOG_E("ftok error: %s\n", strerror(errno)); 
        return SEM_FAILURE; 
    } 

    semid = semget(key, SEM_NUMS, ACCESS_BIT); 
    if(semid < 0) 
    { 
        LOG_E("create sme error: %s\n", strerror(errno)); 
        return SEM_FAILURE; 
    } 

    return semid; 
} 


int sem_p(int semid) 
{ 
    struct sembuf sem_buf; 
    sem_buf.sem_num = 0; 
    sem_buf.sem_op = -1; 
    sem_buf.sem_flg = SEM_UNDO; 

    if(semop(semid, &sem_buf, SEM_OPS_NUM) < 0) 
    { 
        LOG_E("sem P opration error: %s", strerror(errno)); 
        return SEM_FAILURE; 
    } 

    return SEM_SUCCESS; 
} 


int sem_v(int semid) 
{ 
    struct sembuf sem_buf; 
    sem_buf.sem_num = 0; 
    sem_buf.sem_op = 1; 
    sem_buf.sem_flg = SEM_UNDO; 

    if(semop(semid, &sem_buf, SEM_OPS_NUM) < 0) 
    { 
        LOG_E("sem V opration error: %s", strerror(errno)); 
        return SEM_FAILURE; 
    } 

    return SEM_SUCCESS; 
} 


int sem_del(int semid) 
{ 
    union semun sem_union; 
    if(semctl(semid, 0, IPC_RMID, sem_union) < 0)   
    { 
        LOG_E("remove sem error: %s\n", strerror(errno)); 
        return SEM_FAILURE; 
    } 

    return SEM_SUCCESS; 
} 

共享内存系统函数及接口

#include "shmem.h" 
#include "debug.h" 

#define IPCKEY_PATH "/" 
#define ACCESS_BIT 0666 

#define TAG "ShareMem" 

int shm_new(unsigned char PROJID, size_t size) 
{ 
    int shmid; 
    key_t key; 

    key = ftok(IPCKEY_PATH, PROJID); 
    if(key < 0) 
    { 
        LOG_E("get IPC key error: %s\n", strerror(errno)); 
        return SHM_FAILURE; 
    } 

    shmid = shmget(key, size, ACCESS_BIT|IPC_CREAT); 
    if(shmid < 0) 
    { 
        LOG_E("get share mem error: %s\n", strerror(errno)); 
        return SHM_FAILURE; 
    } 

    return shmid; 
} 

char *shem_get_addr(int shmid) 
{ 
    char *p; 

    if((p = (shmat(shmid, NULL, 0))) == (char *)-1) 
    { 
        LOG_E("get share mem addr error: %s\n", strerror(errno)); 
        return NULL; 
    } 

    return p;  
} 

int shm_del(int shmid) 
{    
    if(shmctl(shmid, IPC_RMID, NULL) < 0) 
    { 
        LOG_E("remove share mem error: %s\n", strerror(errno)); 
        return SHM_FAILURE; 
    } 

    return SHM_SUCCESS; 
} 

int shm_detach(char *shmaddr) 
{ 
    if(shmdt(shmaddr) < 0) 
    { 
        LOG_E("share mem detach error: %s\n", strerror(errno)); 
        return SHM_FAILURE; 
    } 
    return SHM_SUCCESS; 
} 

void shm_read(char *buf, char *shmaddr) 
{    
    strncpy(buf, shmaddr, strlen(shmaddr) + 1); 
} 

void shm_write(char *shmaddr, char *buf) 
{    
    strncpy(shmaddr, buf, strlen(buf) + 1); 
} 

void shm_data_init(char *shmaddr) 
{ 
    memset(shmaddr, 0, SHM_SIZE);    
    //strncpy(shmaddr, INIT_DATA, strlen(INIT_DATA) + 1); 
} 

写程序

写进程通过fgets()模拟输入,从终端读取数据写入共享内存,遇到exit时退出程序.

#include <stdlib.h> 
#include <stdio.h> 
#include <unistd.h> 
#include "debug.h" 
#include "sem.h" 
#include "shmem.h" 

#define SEM_PROJID '*' 
#define SHM_PROJID '-' 
#define TAG "SemServer" 
//#define ENDOFSTR '\0' 

#define SHM_SIZE 0x1F4000 


int main() 
{ 
    int semid; 
    int shmid; 
    char *shmaddr; 
    char buf[SHM_SIZE]; 

    semid = sem_new(SEM_PROJID, 1); 
    if(SEM_FAILURE == semid) 
    { 
        exit(-1); 
    } else if(SEM_EXIST == semid) 
    { 
        if((semid = sem_get(SEM_PROJID)) < 0) 
        { 
            exit(-1); 
        } 
        LOG_D("get sem success\n"); 
    } 
    else LOG_D("get new sem success\n"); 

    shmid = shm_new(SHM_PROJID, SHM_SIZE); 
    if(SEM_FAILURE == shmid) 
    { 
        exit(-1); 
    } 

    LOG_D("get share mem success\n"); 

    shmaddr = shem_get_addr(shmid); 
    if(NULL == shmaddr) 
    { 
        exit(-1); 
    } 

    shm_data_init(shmaddr); 
    while(1) 
    { 
        if(fgets(buf, SHM_SIZE, stdin) == NULL) 
        { 
            LOG_E("get std input error: %s", strerror(errno)); 
            exit(-1); 
        } 
        buf[strlen(buf) - 1] = '\0'; 

        sem_p(semid); 
        shm_write(shmaddr, buf); 
        LOG_D("you write : %s\n",buf); 
        sem_v(semid); 

        if(strncmp(buf, "exit", 4) == 0) 
        { 
            LOG_D("process finish exit\n"); 
            break; 
        } 
    } 

    if(shm_detach(shmaddr) == SHM_FAILURE) 
    { 
        exit(-1); 
    } 

    LOG_D("process exit\n"); 

    return 0; 
} 

读程序

读进程通过getchar(),输入回车后, 开始读取共享内存中最新一次的数据.遇到exit后退出程序.

#include <stdlib.h> 
#include <stdio.h> 
#include <unistd.h> 
#include "debug.h" 
#include "sem.h" 
#include "shmem.h" 

#define SEM_PROJID '*' 
#define SHM_PROJID '-' 
#define TAG "SemServer" 

#define SHM_SIZE 0x1F4000 


int main() 
{ 
    int semid; 
    int shmid; 
    char *shmaddr; 
    char buf[SHM_SIZE]; 

    semid = sem_new(SEM_PROJID, 1); 
    if(SEM_FAILURE == semid) 
    { 
        exit(-1); 
    } else if(SEM_EXIST == semid) 
    { 
        if((semid = sem_get(SEM_PROJID)) < 0) 
        { 
            exit(-1); 
        } 
        LOG_D("get sem success\n"); 
    } 
    else LOG_D("get new sem success\n"); 

    shmid = shm_new(SHM_PROJID, SHM_SIZE); 
    if(SEM_FAILURE == shmid) 
    { 
        exit(-1); 
    } 

    LOG_D("get share mem success\n"); 

    shmaddr = shem_get_addr(shmid); 
    if(NULL == shmaddr) 
    { 
        exit(-1); 
    } 

    while(1) 
    { 
        getchar(); 
        sem_p(semid); 
        shm_read(buf, shmaddr); 
        LOG_D("you read : %s\n",buf); 
        sem_v(semid); 

        if(strncmp(buf, "exit", 4) == 0) 
        { 
            LOG_D("process finish exit\n"); 
            break; 
        }    
    } 

    if(shm_del(shmid) == SHM_FAILURE) 
    { 
        exit(-1); 
    } 

    LOG_D("process exit\n"); 

    return 0; 
} 

程序测试: