linux进阶练习题

### 高级 Linux 练习题及答案

#### 进程与线程编程挑战

对于希望深入理解Linux进程和线程机制的人来说，下面是一些具有代表性的练习题：

1. **创建守护进程**
编写一段C代码来创建一个守护进程，在后台持续记录系统的当前时间到指定的日志文件中。该程序应该能够处理SIGTERM信号并优雅退出。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <fcntl.h>

void sigterm_handler(int signum){
    printf("Received SIGTERM\n");
    exit(0);
}

int main(){
    pid_t pid;
    
    /* Fork off the parent process */
    pid = fork();
    
    if (pid < 0) {
        fprintf(stderr, "fork failed!\n");
        exit(EXIT_FAILURE);
    }
        
    // We got a good PID, now detach from terminal.
    if(pid > 0){
        exit(EXIT_SUCCESS);  
    }

    umask(0);

    // Create new SID for child process
    sid = setsid();
    if(sid < 0){
        exit(EXIT_FAILURE);
    } 

    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);

    signal(SIGCHLD,SIG_IGN);
    signal(SIGHUP,SIG_IGN);
    signal(SIGTERM,sigterm_handler);

    while(true){
        FILE *fp=fopen("/var/log/mydaemon.log","a+");
        time_t rawtime;
        struct tm *info;
        char buffer[80];
      
        time(&rawtime);
        info=localtime(&rawtime);
        strftime(buffer,sizeof(buffer),"%Y-%m-%d %H:%M:%S",info);
        fprintf(fp,"%s\n",buffer);
        fclose(fp);
        sleep(60);
    }
}

2. **多线程矩阵乘法**

编写一个多线程应用程序执行两个大尺寸浮点数矩阵相乘操作。每个工作线程负责计算结果矩阵的一行或多行。确保正确同步访问共享资源以防止竞争条件的发生[^1]。

#include <iostream>
#include <pthread.h>
using namespace std;

#define N 4 // Matrix size

float A[N][N], B[N][N], C[N][N];

struct v { int row; }; // Used as argument to thread function

// Function that will be executed by each thread
void* multiply(void* arg){
    struct v *data=(struct v*)arg;
    int sum=0;
    for(int i=0;i<N;++i)
       for(int j=0;j<N;++j)
          C[data->row][j]+=A[data->row][i]*B[i][j];
    pthread_exit(NULL);
}

int main(){
    srand(time(NULL));
    pthread_t threads[N];
    struct v vec[N];

    // Initialize matrices with random values between 0 and 9
    for(int i=0;i<N;++i)
      for(int j=0;j<N;++j){
         A[i][j]=rand()%10;
         B[i][j]=rand()%10;
         C[i][j]=0;
      }

    // Create one thread per matrix row
    for(long t=0;t<N;++t){
       vec[t].row=t;
       pthread_create(&threads[t],NULL,multiply,(void*)&vec[t]);
    }

    // Wait until all threads have completed their work
    for(long t=0;t<N;++t++)
       pthread_join(threads[t], NULL);

    cout << "\nResultant Matrix:\n";
    for(int i=0;i<N;++i){
       for(int j=0;j<N;++j)
           cout<<C[i][j]<<" ";
       cout<<"\n";
    }
    return 0;
}