CODEWITHSUNDEEP
csignalssigaction
WIlopu
WIlopu

Reputation: 47

Using sigaction with or without sigsetjmp

I have an exercise for which I have to implement a function that takes as parameters a one-parameter function pointer fun, a parameter to the function pointed at by said pointer parameter and an integer period. This function will return either 1 in case the execution of the function fun points to with parameter as parameter terminates before period seconds, or 0 if not.

Are these two solutions equivalent?

static struct sigaction sa, old;
static jmp_buf env;

static void myalarm(int sig)
{
  printf("alarm!\n");
  siglongjmp(env,1);
}

int execution_time_limit( void (*fun)(void *), void *parameter, int period)
{
  sa.sa_handler = myalarm;
  sa.sa_flags = 0; 
  sigemptyset(&sa.sa_mask);
  sigaction(SIGALRM, &sa, &old);

  alarm(period);
  if(sigsetjmp(env,1) == 0) {
    fun(parameter);
    sigaction(SIGALRM, &old, NULL);
  }
  else
    return 0;
 return 1;
}

And:

static struct sigaction sa, old;
static jmp_buf env;
int ret = 0;

static void myalarm(int sig)
{
  printf("alarm!\n");
  ret = 1;
}

int execution_time_limit( void (*fun)(void *), void *parameter, int period)
{
  sa.sa_handler = myalarm;
  sa.sa_flags = 0; 
  sigemptyset(&sa.sa_mask);
  sigaction(SIGALRM, &sa, &old);

  alarm(period);
  fun(parameter);
  sigaction(SIGALRM, &old, NULL);
  return ret;
}

I'd say yes, but I'd like to clear up any doubt I might have.

Upvotes: 0

Views: 303

Answers (1)

dbush
dbush

Reputation: 224102

These are not the same.

In the first example, if the alarm is triggered, fun does not exit normally due to the call to siglongjmp. In the second example, the alarm will set the flag for the return value, but fun will continue to run to completion.

Also, you have a bug here:

  if(sigsetjmp(env,1) == 0) 
    fun(parameter);
    sigaction(SIGALRM, &old, NULL);
  else
    return 0
  return 1;

You're missing braces around the if and else blocks, and missing the ; after the first return. Also I believe you have the return values mixed up based on your description of what the function should do.

The fixed code:

  if(sigsetjmp(env,1) == 0) {
    fun(parameter);
    sigaction(SIGALRM, &old, NULL);
  } else {
    return 1;
  }
  return 0;

Upvotes: 1

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