准确处理所有进入 parent 进程的 SIGUSR1 类型的信号。 C

Question

我想编写一个程序，使用 fork() 函数创建 N children。每个 child 将等待 0 到 3 秒，然后它会发送 parent 恰好一个信号 SIGUSR1。 Parent 处理所有这些信号。

问题是我的程序并不总是处理来自 children 的所有信号。如何修复？

第二个问题：我知道我不应该在处理程序中使用 printf，因为可能会发生一些不好的事情。我该如何替换这条指令？

main.c

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

void error(char *s){
    printf("%s\n",s);
    perror("Program execution failed.");
    exit(EXIT_FAILURE);
}

volatile int N=8; //final number of children
volatile int k=0; //number of received SIGUSR1 signals

void childRequestHandler(int signo, siginfo_t* info, void* context){
    k++;
    printf("%d,Father received request from child: %d\n",k,info->si_pid);

}

int main() {
    struct sigaction act;
    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_SIGINFO;
    act.sa_sigaction = childRequestHandler;
    if(sigaction(SIGUSR1,&act,NULL) == -1) printf("ERROR OCCURED");

    for(int i=0;i<N;i++){
        pid_t pid = fork();
        if(pid == 0) {
            execl("./child", "./child", NULL);
            error("Fork error happened\n");
        }
    }

    while (1){
        sleep(1);
    }

}

child.c

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



int main() {
    time_t t;
    srand((unsigned int) getpid()+ time(NULL));


    int length_of_sleeping = rand() % 4 ;
    printf("I live: %d, sleeps %ds \n",getpid(),length_of_sleeping);
    sleep(length_of_sleeping);
    kill(getppid(),SIGUSR1);

    while(1){

    }

}

输出：

I live: 4195, sleeps 3s 
I live: 4196, sleeps 3s 
I live: 4197, sleeps 1s 
I live: 4202, sleeps 3s 
I live: 4198, sleeps 0s 
I live: 4201, sleeps 2s 
I live: 4199, sleeps 0s 
I live: 4200, sleeps 3s 
1,Father received request from child: 4198
2,Father received request from child: 4197
3,Father received request from child: 4201
4,Father received request from child: 4195

Answer 1

当信号处理程序正在执行时，信号被阻塞。在此期间收到的所有 SIGUSR1 个信号将不会被注意到。

您可以在建立信号时使用 SA_NODEFER 标志，有关标志的信息请参阅 the sigaction manual page。

但是，如果您使用 SA_NODEFER，请不要使用 printf！它不是 async-signal-safe 函数。参见例如this manual page about signal safety 获取更多信息。

来自 the POSIX sigaction reference:

When a signal is caught by a signal-catching function installed by sigaction(), a new signal mask is calculated and installed for the duration of the signal-catching function.... This mask is formed by taking the union of the current signal mask and the value of the sa_mask for the signal being delivered, and unless SA_NODEFER or SA_RESETHAND is set, then including the signal being delivered. If and when the user's signal handler returns normally, the original signal mask is restored.

_{[强调我的]}

准确处理所有进入 parent 进程的 SIGUSR1 类型的信号。 C

Handle exactly all signals of type SIGUSR1 that come to parent process. C

c

printf

fork

execl