C语言 如何在 C 中使用等待
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how to use wait in C
提问by jabk
How do i use wait? It just baffles me to no end. I forka tree of procs with recursion and now the children have to pause(wait/sleep) while I run pstree so I can print the proc tree.
我如何使用wait？它只是让我不知所措。我fork是一棵带有递归的 procs 树，现在孩子们在运行 pstree 时必须暂停（等待/睡眠），以便我可以打印 proc 树。
Should i use
我应该使用
int status;
wait(&status);
or rather
更确切地说
wait(NULL)
and where should i put this? in the parent if(pid > 0)or in the children if(pid==0)? Maybe at the end of ifs, so I store all the pids in array and then run a forover them and use wait?
我应该把这个放在哪里？在父母身上if(pid > 0)还是在孩子身上if(pid==0)？也许在 ifs 的末尾，所以我将所有pids存储在数组中，然后for对它们运行 a并使用等待？
my code template:
我的代码模板：
void ProcRec(int index)
{
pid_t pid;
int noChild = getNChild(index);
int i= 0;
for(i = 0; i < noChild; i++)
{
pid = fork();
if (pid > 0)
{
/* parent process */
}
else if (pid == 0)
{
/* child process. */
createProc(index+1);
}
else
{
/* error */
exit(EXIT_FAILURE);
}
}
if(getpid() == root)
{
sleep(1);
pid = fork();
if(pid == 0)
execl("/usr/bin/pstree", "pstree", getppid(), 0);
}
}
回答by Some programmer dude
The waitsystem-call puts the process to sleep and waits for a child-process to end. It then fills in the argument with the exit code of the child-process (if the argument is not NULL).
该wait系统调用使进程睡眠，并等待一个孩子进程结束。然后它用子进程的退出代码填充参数（如果参数不是NULL）。
So if in the parent process you have
所以如果在父进程中你有
int status;
if (wait(&status) >= 0)
{
if (WEXITED(status))
{
/* Child process exited normally, through `return` or `exit` */
printf("Child process exited with %d status\n", WEXITSTATUS(status));
}
}
And in the child process you do e.g. exit(1), then the above code will print
在您执行的子进程中，例如exit(1)，上面的代码将打印
Child process exited with 1 status
Also note that it's important to wait for all child processes. Child processes that you don't wait for will be in a so-called zombie state while the parent process is still running, and once the parent process exits the child processes will be orphaned and made children of process 1.
另请注意，等待所有子进程很重要。当父进程仍在运行时，您没有等待的子进程将处于所谓的僵尸状态，一旦父进程退出，子进程将被孤立并成为进程 1 的子进程。
