c - 我的程序似乎没有终止；为什么？

Question

我正在使用一个叫做 rssgossip.py 的东西在我选择的 rss 提要中搜索一个短语。

基本上，我正在遍历我要搜索的 rss 提要数组，每次我都在 fork 进程并在子进程上调用 execle()。我确实得到了适当的输出，但它看起来很奇怪，然后我的终端就坐在那里等待所有内容打印完毕。

代码

    #include <stdio.h>
    #include <errno.h>
    #include <unistd.h>
    #include <string.h>

    int main(int argc, char *argv[]) {
        char *feeds[] = {"http://feeds.washingtonpost.com/rss/lifestyle",
                     "http://feeds.washingtonpost.com/rss/world",
                     "http://feeds.washingtonpost.com/rss/opinions"};

        int num_feeds = 3;
        if(argc < 2) {
            fprintf(stderr, "You need to tell me a search phrase.\n");
            return 1;
        }
        char *phrase = argv[1];  // this will be the phrase you to search for in the rss feed, passed as an argument
    printf("we are going to search for \"%s\"\n", phrase);
    int i;
    for(i = 0; i < num_feeds; i ++) {
        char var[255];
        sprintf(var, "RSS_FEED=%s", feeds[i]);
        printf("we are going to search this feed: %s\n", var);
        char *my_env[] = {var, NULL};
        // I believe that once we call execle, the while loop stops because we've totally replaced the process! (we need fork...)
        pid_t pid = fork();
        printf("pid: %d\n", pid);
        if(pid == -1) {  // -1 indicates that fork() had a problem cloning the process
            fprintf(stderr, "Can't fork process: %s\n", strerror(errno));
            return 1;
        }
        if(pid == 0) {  // isn't a non-zero number for the parent process?? NO, this is like pid==0, i.e. child process
            printf("running a child process now\n");
            if(execle("/usr/bin/python", "/usr/bin/python",
                    "./rssgossip/rssgossip.py", phrase, NULL, my_env) == -1) {
                fprintf(stderr, "Can't run script: %s\n", strerror(errno));
                return 1;
            }
        }
    }

    return 0;
}

输出

aarons-MacBook-Pro:ch9 aaronparisi$ ./news hi
we are going to search for "hi"
we are going to search this feed: RSS_FEED=http://feeds.washingtonpost.com/rss/lifestyle
pid: 68853
we are going to search this feed: RSS_FEED=http://feeds.washingtonpost.com/rss/world
pid: 68854
we are going to search this feed: RSS_FEED=http://feeds.washingtonpost.com/rss/opinions
pid: 0
running a child process now
pid: 0
running a child process now
pid: 68855
pid: 0
running a child process now
aarons-MacBook-Pro:ch9 aaronparisi$ U.S. general in Afghanistan apologizes for highly offensive leaflets
How Burma's Rohingya crisis went from bad to worse
Sir Richard Branson is riding out Hurricane Irma in the wine cellar on his private island
Britains royal family announces third pregnancy for Duke and Duchess of Cambridge
Fashion is finally figuring out diversity  in ways that actually matter
The Salt Line is an instant hit, with superb seafood and a view to match
The 2017 Washington Post Travel photo contest winners and finalists
Ask Amy: New hire struggles with workplace racism
Hints From Heloise: Kitchen creativity
Miss Manners: Helping a young child deflect questions
A laughing matter
History shows us how calamitous the North Korea crisis could become
These Washington players didnt just stick to their college major
The only thing less fair than the electoral college is the scoring in tennis
With DACA, Jeff Sessions bent Trump to his will - again
Washington Post's Scott Wilson is out as national editor
Who first said, 'The best government is that which governs least'? Not Thoreau.

如您所见，最后没有命令提示符，我的终端只是坐在那里等待。为什么？在打印任何匹配的文章之前出现命令提示符似乎也很奇怪，我也不确定为什么会这样。

Answer 1

您的程序已经终止，但很难看到，因为 fork 的子进程之后继续产生输出。

查看成绩单的中间部分:

running a child process now
aarons-MacBook-Pro:ch9 aaronparisi$ U.S. general in Afghanistan apologizes for highly offensive leaflets

您可以看到您的 shell 在输出中间显示了一个提示，此时原始程序已完成，但子进程仍在运行。

如果您在所有输出完成后点击 [ENTER]，您将看到您的 shell 实际上正在监听并且您将立即收到另一个 shell 提示符。

如果您希望您的程序在所有子进程完成后才退出，您将需要使用 wait(2) 来等待它们完成:http://man7.org/linux/man-pages/man2/waitpid.2.html

如果您的进程没有子进程，由于 wait 返回 -1，您可以在循环中调用它直到它这样做:

int status = 0;
while ((wpid = wait(&status)) > 0);

(我从 Make parent wait for all child processes 得到了那个特定的公式。)