[SOLVED] Failed to make error EINTR with pthread_kill, but succeed with kill

sisrnb · 03-06-2015, 06:18 AM

To do unit test, I want to make sem_wait get error EINTR.
I've written a program below:

Code:

#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <errno.h>

#define PRINTF(fmt, ...)   printf("%s:%d: " fmt, __FUNCTION__, __LINE__, ## __VA_ARGS__)
#define WAIT_INTERVAL      1000

static sem_t sem;

static void sig_handler_drp(int sig)
{
   if (SIGUSR1 == sig)
   {
      PRINTF("SIGUSR1 received\n");
   }
}
void *thread_drp(void *arg)
{
   usleep(WAIT_INTERVAL);
   if (kill(getpid(), SIGUSR1))
   {
      PRINTF("ERROR! kill\n");
   }
//   if (pthread_kill(*(pthread_t *)arg, SIGUSR1))
//   {
//      PRINTF("ERROR! pthread_kill\n");
//   }
   return NULL;
}
int main(int argc, char ** argv)
{
   struct sigaction sa;
   pthread_t tid;

   memset(&sa, 0, sizeof(struct sigaction));
   sa.sa_handler = sig_handler_drp;
   sigemptyset(&sa.sa_mask);
   sa.sa_flags = 0;
   if (-1 == sigaction(SIGUSR1, &sa, NULL))
   {
      PRINTF("ERROR! sigaction\n");
   }
   if (sem_init(&sem, 0, 0))
   {
      PRINTF("ERROR! sem_init\n");
   }
   if (pthread_create(&tid, NULL, thread_drp, &tid))
   {
      PRINTF("ERROR! pthread_create\n");
   }

   if (sem_wait(&sem))
   {
      PRINTF("ERROR! sem_wait\n");
      if (EINTR == errno)
      {
         PRINTF("ERROR! sem_wait gets EINTR\n");
      }
   }

   if (pthread_join(tid, NULL))
   {
      PRINTF("ERROR! pthread_join\n");
   }
   if (sem_destroy(&sem))
   {
      PRINTF("ERROR! sem_destroy\n");
   }

   return 0;
}

The output of the program is:

Code:

sig_handler_drp:19: SIGUSR1 received
main:59: ERROR! sem_wait
main:62: ERROR! sem_wait gets EINTR

If I use pthread_kill instead of kill in function thread_drp,
the program will get stuck by sem_wait.
Why I can't make error EINTR with pthread_kill?

NevemTeve · 03-06-2015, 08:04 AM

Why did you expect you could?

Anyways, change this:

Code:

old:  PRINTF("ERROR! sem_wait\n");
new:  PRINTF("ERROR! sem_wait errno=d: %s\n", errno, strerror (errno));

sisrnb · 03-06-2015, 08:27 AM

Quote:

Originally Posted by NevemTeve

Why did you expect you could?

Anyways, change this:

Code:

old:  PRINTF("ERROR! sem_wait\n");
new:  PRINTF("ERROR! sem_wait errno=d: s\n", errno, strerror (errno));

In my apprehension, using kill() may sometimes affect other threads in the process, but pthread_kill() doesn't.
Maybe I was wrong.

Is that possible with pthread_kill()?

Wow, using strerror() is amazing! Thanks!

SoftSprocket · 03-06-2015, 10:51 AM

Did you read the man page for pthread_kill? You are sending a signal to the thread that is calling pthread_kill and then exiting. While signal handlers are shared pthread_kill only signals the thread whose id is passed. In other words your program is behaving the way it should.

Here is a signal going both ways -all error checking absent and not ready for prime time:

Code:

#include <pthread.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

sig_atomic_t ok = 1;

void handle_sig (int i) {
        ok = 0;
}

void* th (void* arg) {
        int i = 0;
        while (ok) {
                sleep (1);
                printf ("d\n", ++i);
                if (arg != NULL) {
                        printf ("sending d\n", SIGUSR1);
                        pthread_kill (*(pthread_t*)arg, SIGUSR1);
                }
        }

        printf ("Exiting\n");
        return arg;
}

int main () {
        signal (SIGUSR1, handle_sig);

        pthread_t tid;
        
        pthread_create (&tid, NULL, th, NULL);

        sleep (5);
        printf ("sending d\n", SIGUSR1);
        pthread_kill (tid, SIGUSR1);
        pthread_join (tid, NULL);

        ok = 1;
        pthread_t pid = getpid ();
        pthread_create (&tid, NULL, th, &pid);
        
        sleep (5);
        pthread_join (tid, NULL);

        printf ("Goodbye\n");


        return 0;
}

It interrupts the thread then sets up another and tries to kill the parent but this causes a sigfault, which I suspect is because you can't signal the parent this way.

sisrnb · 03-09-2015, 09:30 AM

Quote:

Originally Posted by SoftSprocket

You are sending a signal to the thread that is calling pthread_kill and then exiting.

I meant to send signal to thread main and I thought I was sending to thread main.
Thanks for your reply! Now I've changed the 4th parameter of pthread_create to '&tid_main' which value is given by running pthread_self() in function main, and it works fine.
My program is changed to:

Code:

#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <errno.h>

#define PRINTF(fmt, ...)   printf("%s:%d: " fmt, __FUNCTION__, __LINE__, ## __VA_ARGS__)
#define WAIT_INTERVAL      1000

static sem_t sem;

static void sig_handler_drp(int sig)
{
   if (SIGUSR1 == sig)
   {
      PRINTF("SIGUSR1 received\n");
   }
}
void *thread_drp(void *arg)
{
   usleep(WAIT_INTERVAL);
//   if (kill(getpid(), SIGUSR1))
//   {
//      PRINTF("ERROR! kill\n");
//   }
   if (pthread_kill(*(pthread_t *)arg, SIGUSR1))
   {
      PRINTF("ERROR! pthread_kill\n");
   }
   return NULL;
}
int main(int argc, char ** argv)
{
   struct sigaction sa;
   pthread_t tid;
   pthread_t tid_self = pthread_self();

   memset(&sa, 0, sizeof(struct sigaction));
   sa.sa_handler = sig_handler_drp;
   sigemptyset(&sa.sa_mask);
   sa.sa_flags = 0;
   if (-1 == sigaction(SIGUSR1, &sa, NULL))
   {
      PRINTF("ERROR! sigaction\n");
   }
   if (sem_init(&sem, 0, 0))
   {
      PRINTF("ERROR! sem_init\n");
   }
   if (pthread_create(&tid, NULL, thread_drp, &tid_self))
   {
      PRINTF("ERROR! pthread_create\n");
   }

   if (sem_wait(&sem))
   {
      //PRINTF("ERROR! sem_wait\n");
      PRINTF("ERROR! sem_wait errno=%d: %s\n", errno, strerror (errno));
      if (EINTR == errno)
      {
         PRINTF("ERROR! sem_wait gets EINTR\n");
      }
   }

   if (pthread_join(tid, NULL))
   {
      PRINTF("ERROR! pthread_join\n");
   }
   if (sem_destroy(&sem))
   {
      PRINTF("ERROR! sem_destroy\n");
   }

   return 0;
}