c - 在 C 中处理信号时调用进程的 pid 不正确

Question

我真的不知道我到底做错了什么。我想从传入信号中提取调用者的 pid，但我得到的值完全不正确。

这是我的“捕手”代码:

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>

int SIGNALS_RECEIVED = 0;
pid_t CALLING_PID;

void signal_received(int sig, siginfo_t *info, void *context) {
    SIGNALS_RECEIVED++;

    if(SIGNALS_RECEIVED == 1) {
        CALLING_PID = info->si_pid;
        printf("%ld\n", (long) CALLING_PID);
    }
}

int main() {
    struct sigaction act;
    act.sa_sigaction = &signal_received;

    sigaction(SIGUSR1, &act, NULL);

    while(1) {

    }

    return 0;
}

和“发件人”:

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>

int main(int argc, char **argv) {

    char line[10];
    FILE *cmd = popen("pidof -s catcher", "r");

    fgets(line, 10, cmd);
    pid_t pid = strtoul(line, NULL, 10);

    pclose(cmd);

    int i;
    for(i = 0; i < 400; i++) {
        kill(pid, SIGUSR1);
    }

    kill(pid, SIGUSR2);

    return 0;
}

因此，当先运行 catcher，然后运行 ​​sender 时，我得到:

./catcher 
398533948
SIGNALS_RECEIVED: 24

当发件人的 pid 是:

ps aux | grep *sender
maciej    4704  100  0.0   4328  1268 pts/13   R+   22:46   0:15 ./sender

我的 Linux 版本:

Linux version 4.2.0-34-generic (buildd@lgw01-55) (gcc version 4.8.2 (Ubuntu 4.8.2-19ubuntu1) ) #39~14.04.1-Ubuntu SMP Fri Mar 11 11:38:02 UTC 2016

Answer 1

阅读 sigaction() 的手册页:

sa_handler specifies the action to be associated with signum ... This function receives the signal number as its only argument.

这不是你想要的。你想要这个:

If SA_SIGINFO is specified in sa_flags, then sa_sigaction (instead of sa_handler) specifies the signal-handling function for signum. This function receives the signal number as its first argument, a pointer to a siginfo_t as its second argument ...

您在安装处理程序时没有设置 SA_SIGINFO 标志。

在调用 sigaction 之前将以下行添加到您的代码中:

act.sa_flags = SA_SIGINFO;