父母與子女之間的溝通

Question

我必須編寫一個簡單的C應用程序來創建一個進程和一個子進程（fork（）），我必須執行一個操作。父母初始化值和子計算。我寫這個：

#include <stdlib.h> 
#include <signal.h> 
#include <fcntl.h> 
#include <stdio.h> 
#include <unistd.h> 

typedef struct { 
    int op1; 
    char op; 
    int op2; 
} Operation; 

Operation *varOP; 

void finalResult() 
{ 
    float result = 0; 
    if(varOP->op == '+') result = (varOP->op1 + varOP->op2); 
    if(varOP->op == '-') result = (varOP->op1 - varOP->op2); 
    if(varOP->op == '*') result = (varOP->op1 * varOP->op2); 
    if(varOP->op == '+') result = (varOP->op1/varOP->op2) 
    printf("%f",result); 
} 

int main() { 
    int p; 
    varOP = (Operation *)malloc(sizeof(Operation)); 
    p = fork(); 
    if(p == 0) // If child 
    { 
     signal(SIGUSR1, finalResult); 
     pause(); 
    } 

    if(p > 0) // If parent 
    { 
     varOP->op = '+'; 
     varOP->op1 = 2; 
     varOP->op2 = 3; 
     kill(p, SIGUSR1); 
     wait(NULL); 
    } 
    return 0; 
} 

但我的孩子從來沒有被稱爲。我的代碼有問題嗎？ 感謝您的幫助！

Answer 1

你的示例代碼也有一個更基本的問題：每個進程都有自己的數據空間，所以你通過堆向孩子發送信息的技術將不起作用。一種解決方案是使用管道。這隻增加了四行代碼：

typedef struct { 
    int op1; 
    char op; 
    int op2; 
}Operation; 

Operation *varOP; 

static int pipe_fds[2]; /* <-- added */ 

static void finalResult(void) 
{ 
    float result = 0; 
    read(pipe_fds[0], varOP, sizeof(Operation)); /* <-- added */ 
    if(varOP->op == '+') result = (varOP->op1 + varOP->op2); 
    if(varOP->op == '-') result = (varOP->op1 - varOP->op2); 
    if(varOP->op == '*') result = (varOP->op1 * varOP->op2); 
    if(varOP->op == '/') result = (varOP->op1/varOP->op2); /* <-- typo */ 

    printf("%f\n",result); 
} 

int main (void) 
{ 
    int p; 
    pipe(pipe_fds); /* <-- added */ 
    varOP = (Operation *)malloc(sizeof(Operation)); 
    p = fork(); 

    if(p == 0) // If child 
    { 
     signal(SIGUSR1, finalResult); 
     pause(); 
    } 

    if(p > 0) // If parent 
    { 
     varOP->op = '+'; 
     varOP->op1 = 2; 
     varOP->op2 = 3; 
     write(pipe_fds[1], varOP, sizeof(Operation)); /* <-- added */ 
     kill(p, SIGUSR1); 
     wait(NULL); 
    } 

    return 0; 
} 

Answer 2

當父母呼叫kill()時，可能是孩子尚未執行signal()調用。

Answer 3

謝謝約瑟夫它工作得很好！ 我試圖與內存segementation做到這一點和我有同樣的問題-_-

#include 
#include 
#include 
#include 
#include 

#include 
#include 
#include 

typedef struct { 
    int op1; 
    char op; 
    int op2; 
}Operation; 


int id; 

void hand() 
{ 
    Operation *varOP = (Operation*) shmat(id, NULL, SHM_R); 
    shmdt((char *) varOP): 
    float result = 0; 

    switch (varOP->op) { 
     case '+': 
      result = (varOP->op1 + varOP->op2); 
      break; 
     case '-': 
      result = (varOP->op1 - varOP->op2); 
      break; 
     case '*': 
      result = (varOP->op1 * varOP->op2); 
      break; 
     case '/': 
      result = (varOP->op1/varOP->op2); 
      break; 
     default: 
      result = 0; 
      break; 
    } 

    printf("%f",result); 
    exit(0); 
} 

int main() { 

    int p; 
    key_t cle; 

    p = fork(); 

    cle = ftok(getenv("titi"), 'A'); 
    id = shmget(cle, sizeof(Operation),0); 

    if(p == 0) // Si fils 
    { 
     signal(SIGUSR1,hand); 
     while (1); 
     exit(0); 
    } 

    if(p > 0) 
    { 
     Operation *varOP = (Operation*) shmat(id, NULL, SHM_W); 
     varOP->op = '+'; 
     varOP->op1 = 2; 
     varOP->op2 = 3; 
     shmdt((char *) varOP); 
     kill(p, SIGUSR1); 

     wait(NULL); 
    } 

    return 0; 
}