Subj : trying to make own version of pthread_exit()
To   : comp.programming.threads
From : JS
Date : Tue Mar 22 2005 03:34 pm

I am trying to make my own implementation of pthread_exit(). I have read:

http://www.llnl.gov/computing/tutorials/workshops/workshop/pthreads/man/pthread_exit.html

To prevent confusion I call the funtions mythread instead of pthread.


When a thread calls mythread_exit() it should be terminated safely. But it
should also store a "termination status void pointer" that any joining
threads can access.

When I create a new thread, start_function is called which then calls
mythread_exit with the pointer that it returns. Is this the right use of
pthread_exit function? I store the return value that start_function produces
in a void pointer k.

I can't seem to get k printed to check if the return value was stored in k:


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

typedef int mythread_t;
#define STACK_SIZE 1024

struct pcb {
  void *(*start_routine) (void *);
  void *arg;
  jmp_buf state;
  int stack[STACK_SIZE];
};

typedef struct _mythread_attr_t {
} mythread_attr_t;

static struct pcb first_thread;
struct pcb *current = &first_thread;
struct pcb *ready = NULL;


int mythread_create (mythread_t *threadp,
      const mythread_attr_t *attr,
      void *(*start_routine) (void *),
      void *arg)
{
  int *state_pointer;
  int local_occ;
  struct pcb *pcb_pointer;


  pcb_pointer = (struct pcb *) malloc(sizeof(struct pcb));
  if(pcb_pointer == NULL) {
    exit(-1);
  }

  pcb_pointer->start_routine = start_routine;
  pcb_pointer->arg = arg;

  if(setjmp(pcb_pointer->state)) {

    current->start_routine(current->arg);

    printf("Thread returned - Everything is stopped\n");
    exit(0);
  }

  int JB_BP = 3;
  int JB_SP = 4;

  state_pointer = (int *) &pcb_pointer->state;
  local_occ = state_pointer[JB_BP] - state_pointer[JB_SP];
  state_pointer[JB_BP] = (int) (pcb_pointer->stack + STACK_SIZE);
  state_pointer[JB_SP] = (int) state_pointer[JB_BP] - local_occ;

  ready = pcb_pointer;

  *threadp = (int) pcb_pointer;

  return 0;
}

void mythread_exit(void *retval){
 void * k;
 k = retval;

 printf("%d",k);

}


void *start_function(void *arg){
    int x = 22;
    int *ip;
    ip = &x;

 mythread_exit(ip);


return ip;
}

int main(void){
    mythread_t id;

    mythread_create(&id, NULL, start_function, NULL);
     getchar();
}

.