Question

我需要向一个进程发出信号,而且当进程收到这一信号时,某些事情是怎样的,在C中如何取得最佳成果?

Answer 1

向一个过程发出信号的途径是lu(pid, sign);。然而,你们应当认识到,信号不是除家长与子女之间因固有的种族条件而发出的信息之外的一种强有力的进程间通信手段。管道、档案、目录、名称为ema光、袖珍、共享记忆等,都为处理过程之间的通信提供了高度的优待办法。

Answer 2

If you happen to be on one of the Unix variants, the following man pages will help:

man 2 kill
man 2 signal
man 2 sigvec

Answer 3

kill + fork runnable POSIX example

Time for some fun:

#define _XOPEN_SOURCE 700
#include <assert.h>
#include <signal.h>
#include <stdbool.h> /* false */
#include <stdio.h> /* perror */
#include <stdlib.h> /* EXIT_SUCCESS, EXIT_FAILURE */
#include <sys/wait.h> /* wait, sleep */
#include <unistd.h> /* fork, write */

void signal_handler(int sig) {
    char s1[] = "SIGUSR1
";
    char s2[] = "SIGUSR2
";
    if (sig == SIGUSR1) {
        write(STDOUT_FILENO, s1, sizeof(s1));
    } else if (sig == SIGUSR2) {
        write(STDOUT_FILENO, s2, sizeof(s2));
    }
    signal(sig, signal_handler);
}

int main() {
    pid_t pid;

    signal(SIGUSR1, signal_handler);
    signal(SIGUSR2, signal_handler);
    pid = fork();
    if (pid == -1) {
        perror("fork");
        assert(false);
    } else {
        if (pid == 0) {
            while (1);
            exit(EXIT_SUCCESS);
        }
        while (1) {
            kill(pid, SIGUSR1);
            sleep(1);
            kill(pid, SIGUSR2);
            sleep(1);
        }
    }
    return EXIT_SUCCESS;
}

1. 汇编和操作:

gcc -std=c99 signal_fork.c
./a.out

结果:

SIGUSR1
SIGUSR2
SIGUSR1
SIGUSR2
....

But beware that there are many complexities when dealing with signals:

only certain functions can be called from signal handlers: Why only async-signal-safe functions can be called from signal handlers safely?
different functions have different behaviors when interrupted by signals: man 7 signal, SA_RESTART
global variables can only be accessed from the signal handler if they have type sig_atomic_t: How does sig_atomic_t actually work?

Tested in Ubuntu 17.10, GitHub upstream.

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