有各种选项 waitpid函数（）来帮助你（从POSIX标准引号）：

  

WCONTINUED

  
  

在waitpid函数（）函数应当向由pid的地位，因为它从一个作业控制停止持续尚未见报道指定的任何持续的子进程的状态。

  
  

WNOHANG

  
  

如果状态没有立即由pid指定的其中一个子进程的waitpid函数（）函数不得暂停调用线程的执行。

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在特别WNOHANG将让你看看是否有尸体收集，而不会引起你的进程阻塞，等待尸体。

  

如果调用进程具有SA_NOCLDWAIT设置或具有SIGCHLD设置为SIG_IGN，这个过程没有unwaited，对于转化成僵尸进程的孩子，则调用线程应，直到所有的进程包含调用线程的孩子阻挡终止，等待（）和waitpid函数（）失败，将errno设置为[ECHILD。

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您可能不希望被忽略SIGCHLD等，以及信号处理程序可能应该设置一个标志，告诉主循环哎呀，有死孩子 - 去收集尸体！

。

该SIGCONT和SIGSTOP信号也将是相关的你 - 它们被用来启动和停止子进程，分别为（在这种情况下，在任何速度）

我建议在看Rochkind的书或史蒂文斯的书 - 他们详细讨论这些问题。

。

In this previous question I posted most of my own shell code. My next step is to implement foreground and background process execution and properly wait for them to terminate so they don't stay as "zombies".

Before adding the possibility to run them in the background, all processes were running in the foreground. And for that, I simply called wait(NULL) after executing any process with execvp(). Now, I check for the '&' character as the last argument and if it's there, run the process in the background by not calling wait(NULL) and the process can run happily in the background will I'm returned to my shell.

This is all working properly (I think), the problem now, is that I also need to call wait() (or waitpid() ?) somehow so that the background process doesn't remain "zombie". That's my problem, I'm not sure how to do that...

I believe I have to handle SIGCHLD and do something there, but I have yet to fully understand when the SIGCHLD signal is sent because I tried to also add wait(NULL) to childSignalHandler() but it didn't work because as soon as I executed a process in the background, the childSignalHandler() function was called and consequently, the wait(NULL), meaning I couldn't do anything with my shell until the "background" process finished. Which wasn't running on the background anymore because of the wait in the signal handler.

What am I missing in all this?

One last thing, part of this exercise I also need to print the changes of the processes status, like process termination. So, any insight on that is also really appreciated.

This is my full code at the moment:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <wait.h>
#include <signal.h>
#include <sys/types.h>

#include "data.h" // Boolean typedef and true/false macros


void childSignalHandler(int signum) {
    //
}

int main(int argc, char **argv) {
    char bBuffer[BUFSIZ], *pArgs[10], *aPtr = NULL, *sPtr;
    bool background;
    ssize_t rBytes;
    int aCount;
    pid_t pid;

    //signal(SIGINT, SIG_IGN);

    signal(SIGCHLD, childSignalHandler);

    while(1) {
    	write(1, "\e[1;31mmyBash \e[1;32m# \e[0m", 27);
    	rBytes = read(0, bBuffer, BUFSIZ-1);

    	if(rBytes == -1) {
    		perror("read");
    		exit(1);
    	}

    	bBuffer[rBytes-1] = '\0';

    	if(!strcasecmp(bBuffer, "exit")) {
    		exit(0);
    	}

    	sPtr = bBuffer;
    	aCount = 0;

    	do {
    		aPtr = strsep(&sPtr, " ");
    		pArgs[aCount++] = aPtr;
    	} while(aPtr);

    	background = FALSE;

    	if(!strcmp(pArgs[aCount-2], "&")) {
    		pArgs[aCount-2] = NULL;
    		background = TRUE;
    	}

    	if(strlen(pArgs[0]) > 1) {
    		pid = fork();

    		if(pid == -1) {
    			perror("fork");
    			exit(1);
    		}

    		if(pid == 0) {
    			execvp(pArgs[0], pArgs);
    			exit(0);
    		}

    		if(!background) {
    			wait(NULL);
    		}
    	}
    }

    return 0;
}

There are various options to waitpid() to help you (quotes from the POSIX standard):

WCONTINUED

The waitpid() function shall report the status of any continued child process specified by pid whose status has not been reported since it continued from a job control stop.

WNOHANG

The waitpid() function shall not suspend execution of the calling thread if status is not immediately available for one of the child processes specified by pid.

In particular, WNOHANG will allow you to see whether there are any corpses to collect without causing your process to block waiting for a corpse.

If the calling process has SA_NOCLDWAIT set or has SIGCHLD set to SIG_IGN, and the process has no unwaited-for children that were transformed into zombie processes, the calling thread shall block until all of the children of the process containing the calling thread terminate, and wait() and waitpid() shall fail and set errno to [ECHILD].

You probably don't want to be ignoring SIGCHLD, etc, and your signal handler should probably be setting a flag to tell your main loop "Oops; there's dead child - go collect that corpse!".

The SIGCONT and SIGSTOP signals will also be of relevance to you - they are used to restart and stop a child process, respectively (in this context, at any rate).

I'd recommend looking at Rochkind's book or Stevens' book - they cover these issues in detail.