SIGCHLD在Linux上的SIGCONT上发送，但在macOS上不发送 [英] SIGCHLD is sent on SIGCONT on Linux but not on macOS

问题描述

在主要过程中，我听SIGCHLD:

In the main process I listen to SIGCHLD:

signal(SIGCHLD, &my_handler);

然后我fork()，execv()并使其在后台运行(例如，/bin/cat).

Then I fork(), execv() and let it run in background (/bin/cat for example).

当我尝试从终端将SIGSTOP发送到子进程时，会调用my_handler().但是，当我尝试向其发送SIGCONT时，该处理程序未在macOS上调用，而是在我的Ubuntu上执行.

When I try from terminal to send SIGSTOP to the child process, my_handler() gets called. But when I try to send SIGCONT to it, the the handler isn't called on macOS but it's executed on my Ubuntu.

男人:

SIGCHLD:子状态已更改.

SIGCHLD: child status has changed.

我错过了什么吗?这是预期的行为吗?我在Ubuntu上编写了我的应用程序，并期望它也可以在Mac上运行.

Am I missing something? Is it an expected behaviour? I wrote my app on Ubuntu and expected it to work on mac as well.

我也尝试过使用sigaction()，但结果相同.

I tried with sigaction() as well, but with the same results.

下面是一个示例代码来演示:

Here's a sample code to demonstrate:

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

void    my_handler(int signum)
{
    printf("\t SIGCHLD received\n");
    fflush(stdout);
}

void    my_kill(pid_t pid, int signum)
{
    printf("Sending %d\n", signum);
    fflush(stdout);

    kill(pid, signum);

    printf("Sent %d\n\n", signum);
    fflush(stdout);
}

int main()
{
    pid_t   pid;
    char    *cat_args[2] = {"/bin/cat", NULL};

    signal(SIGCHLD, &my_handler);
    pid = fork();

    if (pid == 0)
    {
        execv("/bin/cat", cat_args);
    }
    else
    {   
        my_kill(pid, SIGSTOP);
        my_kill(pid, SIGCONT);
        wait(NULL);
    }
    return 0;
}

在macOS上的输出:

With the output on macOS:

Sending 17
         SIGCHLD received
Sent 17

Sending 19
Sent 19

推荐答案

该行为是可选的.实现无需在继续时生成SIGCHLD. POSIX.1-2008(2016版)中使用的语言是可以"而不是应该":

That behavior is optional. An implementation need not generate a SIGCHLD upon continuation. The language used in POSIX.1-2008 (2016 edition) is "may" rather than "shall":

当继续停止的进程时，除非其父进​​程设置了SA_NOCLDSTOP标志，否则可能为其父进程生成SIGCHLD信号 .

-系统接口，2.4.3信号操作

...只要其停止的子进程中的任何一个继续执行，就会为调用进程生成SIGCHLD信号 .

- 系统接口sigaction说明"

- System Interfaces sigaction "Description"

添加了重点.

这篇关于SIGCHLD在Linux上的SIGCONT上发送，但在macOS上不发送的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！