1. Each thread's static storage (i.e., Thread Specific Storage) keeps both its error count and the thread's name;
2. When an FPE trap is fired, the thread display's its name and current error count.(hint: use a structure).

Questions:

Normally a process has one set of handlers and one thread, so what should de done for a multithreaded process when it fires a trap? Should a new thread be created, use the main thread, or what option (s) are (reasonably) possible?

#define _REENTRANT_                    /* a flag */

 

#include <stdio.h>

#include <stdlib.h>

#include <signal.h>

#include <thread.h>

#include <setjmp.h>

 

thread_key_t errorkey;     /* key to access the Thread Specific Storage */

 

sigjmp_buf sjbuf;

 

void grace(int );

 

void * foo(void *datum)

{int x,y,z;

int *error_count;

thr_getspecific(errorkey, ( void *) &error_count);

         if ( error_count == NULL) {

                error_count = (int *) malloc( sizeof(int) );

                thr_setspecific(errorkey, (int *) error_count);

                *error_count = 0;

}

 

sigset( SIGFPE, grace); /* establish handler */

while (1) {

if (sigsetjmp(sjbuf,1) == 0)

{

// sigsetjmp(sjbuf,1 ); /* remember this point */

x = rand()%5;

y = rand()%5;

z = x / y;

printf("thread %s has computed %d=%d/%d\n", (char *) datum, z,x,y);

}

}

printf("error_count points to :=== %x\n", *error_count);

}

void _doom(void * S) /* destructor automatically called and given the */

{ /* slot contents */

free( S );

}

#define NTHR 2

#define MAX_TRIES 3

char *name[] = { "Ali",

"Doug",

"Yoon",

"" /* NULL string */

};

int error_count_int=0;

void main(void)

{ int i=0;

thread_t thr[NTHR];

thr_keycreate(&errorkey, &_doom);

for(i=0; i<NTHR; i++)

{

thr_create(NULL, NTHR , foo(name[i]), (void *) name[i], THR_BOUND, &thr[i]);

printf(" THR_BOUND :=== %x\n", THR_BOUND);

}

while ( thr_join(thr[1], thr, NULL) == 0);

foo(name[i]);

}

void grace(int sig) /* signal handler */

{ void *error_count=NULL;

thr_getspecific(errorkey, (void *) &error_count);

error_count_int = (int *) error_count;

printf("\n error_count_int :=== %d \n", error_count_int);

error_count_int++;

if ( (error_count_int) > MAX_TRIES) {

printf("Thread exceeds max error attempts\n");

thr_exit(0);

}

else { /* try again */

printf("Aborting current computation\n");

siglongjmp( sjbuf, 1);

}

}