了解SIGCHLD当子进程结束 [英] Understanding SIGCHLD when the child process terminates

问题描述

我不能够理解以下程序的输出。我观察到，子进程返回后，父进程不睡觉，持续3秒的等待（）之前。如果SIGCHLD被设置为默认的处理器，那么它睡了3秒，调用wait和返回预期。究竟是什么在这里发生的？

 ＃包括LT＆;＆unistd.h中GT;
＃包括LT＆; SYS / types.h中＆GT;
＃包括LT＆;＆stdio.h中GT;
＃包括LT＆; SYS / wait.h＆GT;
＃包括LT＆;＆signal.h中GT;无效的处理程序（INT SIG）{
的printf（荫中处理... \\ n）;
}主（）{INT状态;
将为pid_t PID;结构sigaction的行为;
//act.sa_flags=SA_NOCLDSTOP;
act.sa_handler =处理程序;
的sigaction（SIGCHLD，＆安培;行为，NULL）;如果（！叉（））{
的printf（子进程ID为％d \\ n，GETPID（））;
 返回1;
}的printf（XXX ... \\ n）;
睡眠（3）;
PID =等待（安培;状态）;
的printf（终止进程为％d \\ n，PID）;}输出::XXX ...
子进程ID是2445
在荫...处理器
终止的进程是2445
 

解决方案

在子进程死一个 SIGCHLD 发送给家长。在你的情况下，它会中断睡眠，它看起来仿佛过程不睡觉。

问题的要点：睡眠时，信号中断是没有重新启动

I am not able to understand the output for the following program. I observed that after the child process returns, parent process is not sleeping for 3 sec before wait(). If SIGCHLD is set to default handler, then it sleeping for 3 sec, calling wait and returning as expected. What is exactly happening here ??

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

void handler(int sig) {
printf("Iam in handler ...\n");
}

main() {

int status;
pid_t pid;

struct sigaction act;
//act.sa_flags=SA_NOCLDSTOP;
act.sa_handler=handler;
sigaction(SIGCHLD,&act,NULL);

if(!fork()) {
printf("child process id is  %d\n",getpid());
 return 1;
}  

printf("xxx ...\n");
sleep(3);
pid = wait(&status);
printf("process terminated is %d\n",pid);

}

output::

xxx ...
child process id is  2445
Iam in handler ...
process terminated is 2445

解决方案

When the child process dies a SIGCHLD is sent to the parent. In your case it interrupts the sleep and it looks as if the process doesn't sleep.

The gist of the issue: sleep isn't restarted when interrupted by a signal.

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