Question

我正在尝试在C中创建处理器场。我首先打开消息队列，然后尝试创建工作进程:(注意NROF_WORKERS是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，我希望父母在任何时候创建一个孩子，然后我希望父母和所有孩子都要报告。但是，这就是我得到的：

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

现在，我注意到11909和11914的区别是5.所以我的问题是：是否创建了其他进程？如果是这样，他们怎么不报告？如果没有，我做错了什么？此外，父母根本没有报道，这是怎么造成的？

Answer 1

所有子节点都已创建，但会在while循环中永久循环，因为i仅针对父节点递增：

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();
    }
}

唯一要终止的孩子是最后一个，i等于NROF_WORKERS。

父母也是＆＃34;没有报告＆＃34;因为你检查的processID等于父PID永远不等于它，因为它等于最新的fork结果，即最新创建的子PID：

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

Answer 2

您始终打印farmerPid！但是，当消息被打印5次时，您有效地创建了5个过程：

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

如果您想打印子pids，那么您的代码必须在父级和子级之间产生影响，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);
        }
    }
}

5叉后只有1个孩子（C）

2 个答案: