如何在C中阻止信号?

问题描述

我正在尝试创建一个阻止信号SIGUSR1的程序，并且它将取消阻止该信号.在中间，我想使用sigpending阻止信号.但是它总是说信号没有被阻塞，在应该被阻塞的情况下我可以使用该信号.这是我的代码.

I'm trying to create a program that blocks the signal SIGUSR1 and the it unblocks the signal.In the middle I want to see that the signal is blocked using sigpending. But it always says that the signal isn't blocked, and I can use the signal when it's supposed to be blocked.This is the code that I have.

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

static void signals(int signaln)
{
  switch (signaln) {
  case SIGUSR1:
    printf("Signal SIGUSR1\n"); break;
  }
  return;
}
main()
{
  sigset_t set,set2;
  struct sigaction sigs;
  sigs.sa_handler = signals;
  sigemptyset(&sigs.sa_mask);
  sigs.sa_flags=SA_ONESHOT;
  sigaction(SIGUSR1, &sigs,0);
  sigemptyset(&set);
  sigemptyset(&set2);
  sigaddset(&set,SIGUSR1);
  if(sigprocmask(SIG_BLOCK, &set, NULL)==0){
    printf("Blocking SISGUSR1...\n");
  }
  sigpending(&set2);
  if (sigismember(&set2,SIGUSR1)==1)
  {
    printf("The signal is blocked\n");  //it should print this
  }
  wait(2);
  kill(getpid(),SIGUSR1); //the signal shouldn't work
  wait(2);
  if(sigprocmask(SIG_UNBLOCK, &set, NULL)==0){
    printf("Unblocking SIGUSR1\n");
  }
}

有人可以帮我吗?

推荐答案

sigpending不会告诉您信号是否被阻止.它告诉您是否正在等待发送信号. (即，信号被 阻止了，并且已经发送了一个信号.)

sigpending doesn't tell you whether a signal is blocked. It tells you whether a signal is waiting to be delivered. (i.e., the signal is blocked and one has been sent.)

此外，被阻止并不意味着信号将不会被传递；这意味着该信号现在将不再发送.因此，您可以发送信号，并且在信号被解除阻塞后将立即发送该信号.可能在调用sigprocmask(SIGUNBLOCKED...)之后但在调用printf之前，所以您可能会在看到取消阻止"消息之前看到已收到信号的消息.

Also, blocked doesn't meean that the signal won't be delivered; it means that the signal won't be delivered now. So you can send the signal, and it will be delivered as soon as the signal is unblocked; probably after the call to sigprocmask(SIGUNBLOCKED...) but before the call to printf, so you'll probably see the signal received message before you see the "unblocking" message.

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