Question

我正在使用名为rssgossip.py的内容来搜索我选择的RSS Feed中的短语。

基本上，我正在迭代我要搜索的一系列rss提要，每次我都要分配进程并在子进程上调用execle()。我确实得到了合适的输出，但它看起来很奇怪，然后我的终端只是坐在那里等待一切打印完毕。

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.

正如你所看到的，最后没有命令提示符，我的终端只是坐在那里等待。为什么？在打印任何匹配文章之前显示命令提示符似乎很奇怪，不知道为什么会发生这种情况。

Answer 1

您的程序已经终止，但很难看到，因为分叉的子进程继续产生输出。

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，在原始程序完成时，但子进程仍在运行时。

如果您在完成所有输出后只按[ENTER]，您将看到您的shell实际上正在侦听，并且您将立即获得另一个shell提示。

如果您希望程序在完成所有子进程之后才退出，则需要使用wait（2）等待它们完成：http://man7.org/linux/man-pages/man2/waitpid.2.html

如果你的进程没有子进程，则wait返回-1，你可以在循环中调用它，直到它为止：

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

（我从Make parent wait for all child processes得到了具体的公式。）

我的程序似乎没有终止;为什么呢？

1 个答案: