进程锁 读写文件的小例子 C++代码

代码

#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <cassert>
#include <pthread.h>
#include <cstdio>
#include <cstdlib>
#include <fstream>
#include <iostream>
#include <sstream>
#include <cstring>
#include <sys/wait.h>

/**
 *  返回一片共享内存标识符，用于后续获取该共享内存，以及销毁该共享内存
 */
        class mutex_function{
        public:
            mutex_function() = default;
            // 定义进程锁结构体
            typedef struct mutex_struct{
                pthread_rwlock_t lock;
                pthread_rwlockattr_t lock_attr;
                int memory_addr;
            }mutex_struct_t;

            int create_share_memory_id(const int index_of_key,size_t md5){
                const char* file_path = "./";
                key_t id = ftok(file_path,md5);
                const int share_memory_id = shmget(id,md5,IPC_CREAT | 0666);
                if (share_memory_id == -1){
                    std::cout << "share_memory_id error!\n" << std::endl;
                    exit(EXIT_FAILURE);
                }else{
                    return share_memory_id;
                }
            }

            // 初始化进程锁结构体
            int init_mutex_struct(mutex_struct_t* mutex_ptr){
                pthread_rwlockattr_init(&(mutex_ptr->lock_attr));
                pthread_rwlockattr_setpshared(&(mutex_ptr->lock_attr),PTHREAD_PROCESS_SHARED);
                pthread_rwlock_init(&(mutex_ptr->lock),&(mutex_ptr->lock_attr));
                return 0;
            }
            // 在共享内存上定义进程锁结构体并且返回其位置
            mutex_struct_t* mutex_struct_addr(const int index){
                int memory_id = create_share_memory_id(index,sizeof (mutex_struct_t));
                mutex_struct_t * share_ptr = (mutex_struct_t* )shmat(memory_id, 0, 0);
                if (share_ptr == (void *)-1){
                    std::cout << "share_ptr error!\n" << std::endl;
                    exit(EXIT_FAILURE);
                }
                share_ptr->memory_addr = memory_id;
                assert(init_mutex_struct(share_ptr)== 0);
                return share_ptr;
            }

            // 销毁进程锁结构体，利用其memory_addr变量索引到其占用的共享内存并销毁
            const int destroy_mutex_memory(mutex_struct_t * mutex_struct){
                pthread_rwlock_destroy(&(mutex_struct->lock));
                pthread_rwlockattr_destroy(&(mutex_struct->lock_attr));
                assert(shmctl(mutex_struct->memory_addr,IPC_RMID, nullptr) == 0);
                return 0;
            }
        public:
            mutex_struct_t* mutex_struct_ptr;
        };

//read file
void read_file(const std::string file_name,int id){
    std::ifstream fp(file_name,std::ios::binary);
    std::stringstream ss;
    ss << fp.rdbuf();

    std::cout << "线程"<< id << "抢占了资源,输出:" << ss.str() << std::endl;
    sleep(3);
    std::cout << "线程"<< id << "释放了资源...\n" << std::endl;
    fp.close();
}
//write file
void write_file(const char *file_name,char *str,int id){
    FILE *fd = fopen(file_name,"a+");
    if (fd == nullptr){
        printf("fd is nullptr and open file fail\n");
    } else{
        std::cout <<"线程"<< id << "抢占了资源" << std::endl;
        fwrite(str,strlen(str),1,fd);
        char *next = "\0";
        fwrite(next,strlen(next),1,fd);
        sleep(5);
        std::cout << "线程"<< id << "释放了资源...\n" << std::endl;

    }
    fclose(fd);
}
int main(){
    std::string file_name = "/home/gsc/Projects/1.txt";
    char * str1 = "progress 1\n";
    char * str2 = "progress 2\n";

    // 创建自定义进程锁
    hsm::hal::mutex_function mutex_function_object;
    mutex_function_object.mutex_struct_ptr = mutex_function_object.mutex_struct_addr(111);
    
    pid_t c_pid = fork();

    if (c_pid == -1) {
        perror("fork");
        exit(EXIT_FAILURE);
    } else if (c_pid > 0) {
        std::cout << "Parent process " << getpid() << std::endl;
//            pthread_rwlock_rdlock(&(mutex_function_object.mutex_struct_ptr->lock));
//            read_file(file_name,getpid());
//            pthread_rwlock_unlock(&(mutex_function_object.mutex_struct_ptr->lock));

        pthread_rwlock_wrlock(&(mutex_function_object.mutex_struct_ptr->lock));
        write_file(file_name.c_str(),str1,getpid());
        pthread_rwlock_unlock(&(mutex_function_object.mutex_struct_ptr->lock));

        wait(nullptr);
    } else {
        std::cout << "Child process " << getpid() << std::endl;

        pthread_rwlock_rdlock(&(mutex_function_object.mutex_struct_ptr->lock));
        read_file(file_name,getpid());
        pthread_rwlock_unlock(&(mutex_function_object.mutex_struct_ptr->lock));

//        pthread_rwlock_wrlock(&(mutex_function_object.mutex_struct_ptr->lock));
//        write_file(file_name.c_str(),str2,getpid());
//        pthread_rwlock_unlock(&(mutex_function_object.mutex_struct_ptr->lock));

        exit(EXIT_SUCCESS);
    }

    return 0;
}