[SOLVED] Signal handling in pthread

[kingsmasher1]

Hi All,
I have created a pthread, and installed a signal handler inside that, same way as we do in main( ) function. The thread's signal handler is a separate function. Surprisingly, it is not working, that is the thread's signal handler is not able to catch signals. Here is the code:

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

typedef struct data
{
 char name[10];
 int age;
}data;

void sig_func(int sig)
{
 printf("Caught signal: %d\n",sig);
 signal(SIGSEGV,sig_func);
}

void func(data *p)
{
 printf("This is from thread function\n");
 signal(SIGSEGV,sig_func); // Register signal handler inside thread
 strcpy(p->name,"Mr. Linux");
 p->age=30;
 sleep(2); // Sleep to catch the signal
}

int main()
{
 pthread_t tid;
 pthread_attr_t attr;
 data *ptr;

 pthread_attr_init(&attr);
 pthread_create(&tid,&attr,(void*)func,ptr);
 pthread_kill(tid,SIGSEGV);

 pthread_join(tid,NULL);
 printf("Name:%s\n",ptr->name);
 printf("Age:%d\n",ptr->age);
}

Output:
Segmentation fault (which means the signal is not caught by handler)

[kingsmasher1]

The problem is sorted:
1) ptr is not initialised, so all the ptr-> parts will crash the program
2) you are calling pthread_kill() immediately, very likely before the signal handler has been installed, and in a thread (which has unspecified behaviour)
3) you call printf() from a signal handler, which is not guaranteed to work (see man 7 signal for a list of safe functions)
Here is the modified code: Thanks to Sam Hocevar, who helped me solve this (User Sam Hocevar - Stack Overflow)

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

typedef struct data
{
 char name[10];
 int age;
}data;
void sig_func(int sig)
{
 printf("Caught signal:%d\n",sig);
 signal(SIGSEGV,sig_func);
}

void func(data *p)
{
 fprintf(stderr,"This is from thread function\n");
 signal(SIGSEGV,sig_func);
 strcpy(p->name,"Raj");
 p->age=30;
 sleep(2);
}

int main()
{
pthread_t tid;
 pthread_attr_t attr;
 data *ptr,d;
 ptr=&d;

 pthread_attr_init(&attr);
 pthread_create(&tid,&attr,(void*)func,ptr);
 sleep(2);

 pthread_kill(tid,SIGSEGV);
 pthread_join(tid,NULL);
 printf("Name:%s\n",ptr->name);
 printf("Age:%d\n",ptr->age);
}