只有1名兒童在5個叉（C）

Question

我試圖在C.處理器農場我先開口消息隊列，事後儘量使工作進程：（注意NROF_WORKERS 5）

static void 
makechildren (void) { 
    // Only the parent should fork. Any children created will become workers. 
    pid_t processID; 
    pid_t farmerPID = getpid(); // To identify who the farmer is 

    // Loop creating processes, indexed by NROF_WORKERS 
    int i = 0; 
    while (i < NROF_WORKERS){ 
     if (getpid() == farmerPID){ 
      i++; 
      printf ("Parent is creating a child!%d\n", getpid()); 
      processID = fork(); 
     } 
    } 

    if (processID < 0){ 
     perror("fork() failed"); 
     exit(1); 
    } 
    else { 
    // If parent, start farming 
     if (processID == farmerPID) { 
      printf("Parent reporting in!%d\n"); 
     } 
    // If child, become a worker 
     if (processID == 0) { 
      printf("Child reporting in!%d\n", getpid()); 
      join(); 
     } 
    } 
} 

正如您所看到的，我希望父母在任何時候創建孩子時都會報告，之後我希望父母和所有孩子都能報告。然而，這是我得到的：

Parent is creating a child!11909 
Parent is creating a child!11909 
Parent is creating a child!11909 
Parent is creating a child!11909 
Parent is creating a child!11909 
Child reporting in!11914 

現在，我注意到在11909的差異，11914是5。所以我的問題：是對其他進程產生的？如果是這樣，他們怎麼不報告？如果不是，我做錯了什麼？另外，家長根本沒有報告，這是如何引起的？

Answer 1

所有的孩子都創建，但將永遠循環下去，在while循環，爲i只父遞增：

int i = 0; 
while (i < NROF_WORKERS){ 
    if (getpid() == farmerPID){  
     i++;    // <---- This is happening for the parent process only. 
     printf ("Parent is creating a child!%d\n", getpid()); 
     processID = fork(); 
    } 
} 

終止獨生子女是最後一個，爲此i等於NROF_WORKERS。

而且父「未報告」以來，processID要檢查等於父PID是永遠等於它，因爲它是等於最近fork結果，即最近創建的子PID：

......... 
processID = fork(); 
......... 
......... 
if (processID == farmerPID) { 
      printf("Parent reporting in!%d\n"); 
} 

Answer 2

您總是打印farmerPid！但是，隨着信息打印5次，將有效地創建5個流程：

while (i < NROF_WORKERS){ 
    if (getpid() == farmerPID){ 
     i++; 
     printf ("Parent is creating a child!%d\n", getpid()); 
     processID = fork(); 
    } 
} 

如果你要打印的孩子的PID那麼你的代碼必須使得父母與孩子之間的差異，如：

while (i < NROF_WORKERS){ 
    if (getpid() == farmerPID){ 
     i++; 
     printf ("Parent is creating a child!\n"); 
     processID = fork(); 
     if (processID==0) { // child 
      printf("I am the child %d\n",getpid()); 
     } else { // parent 
      printf("Parent just created child %d\n",processID); 
     } 
    } 
}