信号处理用C - 中断中断 [英] Signal handling in C - interrupt in interrupt

问题描述

我在想，如果有可能，我的计划是在同一时间处理其它信号可以通过一个信号中断，我试图以模拟吧：

I was wondering if it is possible to be interrupted by a signal when my program is handling other signal at the same time, I tried to simulate it with:

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

void sig_output()
{
    sigset_t set;
    sigprocmask(0,NULL,&set);
    printf("currently blocking:");
    if (sigismember(&set,SIGUSR1))
        printf("\nSIGUSR1");
    if(sigismember(&set,SIGUSR2))
        printf("\nSIGUSR2");
    printf("\n");
    return ;
}

void sig_handler(int sig)
{
    raise(SIGUSR1);    
    printf("start\n");
    if (sig==SIGUSR1)
        printf("SIGUSR1\n");
    else if (sig==SIGUSR2)
        printf("SIGUSR2\n");
    printf("end\n");
    return ;
}

void other_sig_handler(int sig)
{  
    printf("start - other\n");
    if (sig==SIGUSR1)
        printf("SIGUSR1\n");
    else if (sig==SIGUSR2)
        printf("SIGUSR2\n");
    printf("end - other\n");
    return ;
}

int main()
{
    sig_output();
    struct sigaction a;
    a.sa_handler=sig_handler;
    a.sa_flags=0;
    sigset_t set,old;
    //blocking SIGUSR1,SIGUSR2
    sigemptyset(&set);
    sigaddset(&set,SIGUSR1);
    sigaddset(&set,SIGUSR2);
    printf("blocking SIGUSR1, SIGUSR2\n");
    sigprocmask(SIG_SETMASK,&set,&old);
    sig_output();
    //adding handles for SIGUSR1,SIGUSR2
    sigemptyset(&(a.sa_mask));
    sigaction(SIGUSR1,&a,NULL);
    a.sa_handler=other_sig_handler;
    sigaction(SIGUSR2,&a,NULL);
    printf("poczatek wysylania \n");
    raise(SIGUSR1);
    raise(SIGUSR2);
    raise(SIGUSR1);
    printf("using sigsuspend\n");
    sigsuspend(&old);
    printf("end of program\n");
    return 0;
}

和每次我运行这个程序，我得到

and everytime I run this program I get

currently blocking:
blocking SIGUSR1, SIGUSR2
currently blocking:
SIGUSR1
SIGUSR2
raising
using sigsuspend
start - other
SIGUSR2
end - other
start
SIGUSR1
end
end of program

是它总是这样？

推荐答案

引述的sigaction（2）手册页：

信号程序通常与导致信号执行其
  调用阻止，但是还可能发生其它的信号。一个全球性的信号掩码
  定义了一套从目前交付给一个进程阻塞信号。
  一个进程的信号掩码是从其父初始化
  （通常为空）。它可以与 sigprocmask改变（2）电话，或当
  信号被传递到过程

Signal routines normally execute with the signal that caused their invocation blocked, but other signals may yet occur. A global signal mask defines the set of signals currently blocked from delivery to a process. The signal mask for a process is initialized from that of its parent (normally empty). It may be changed with a sigprocmask(2) call, or when a signal is delivered to the process.

您可以控制​​信号是否被自动阻止与 SA_NODEFER 标志其信号处理程序。

You can control whether the signal is automatically blocked in its signal handler with the SA_NODEFER flag.

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