user thread library

[Eran]

Hi,
I'm trying to implement a simple user thread library. all threads are stored in a 'ready' state queue, and when the timer runs out of time a signal causes a signal handler to switch to the next ready thread.
now i'm having a segmentation fault, and couldn't find the reason. it happens during the longjmp call (setting registers back to previous state...), and seems to be like the jmp_buf isn't set correctly.
valgrind tells me:
'conditional jump or move depends on uninitialised values...
at.... sigprocmask
at... lonjmp
at... dispatch' <-- my signal handler

this error occurs in the first call to dispatch, so i guess i'm not setting right something in the thread's initializer. the functions i use are thread_spawn(void (*f)(void)) which is the .h function, and thread_init(** thread) which is called by thread_spawn.

the struct:

typedef struct{
  struct thread_status status;
  int state;
  jmp_buf *env;
  char *stack;
} thread;

the functions:

int thread_init(thread **new_thread) {
  if ((*new_thread =(thread *)malloc(sizeof(thread))) == NULL)
    return FAILED;	
  if (((*new_thread)->env =(jmp_buf *)malloc(sizeof(jmp_buf))) == NULL) {
    FREE(*new_thread);
    return FAILED;
  }  
  (*new_thread)->stack = (char*)malloc(STACKSIZE);
  if (!(*new_thread)->stack) {
    FREE(*new_thread);
    FREE(*new_thread);
    return FAILED;
  }  

  (*new_thread)->state = READY;
  ((*new_thread)->status).bursts = 0;
  return SUCCESS;  
}
  

int thread_spawn(void (*f)(void)){
  sigset_t set;            // starting termination process,
  mask_all_signals(&set);  // masking all signals.
  if (running_thread == -1)
    process_init();      // if first call, init process and MAIN thread
  
  if (tids.empty())
    return FAILED;       // if no more thread ids to allocate, fail
  
  thread *newthread;
  if(!thread_init(&newthread))
    return FAILED;		 // if could not initialize the thread, fail 
  //setjmp(*(newthread->env));
  ((*(newthread->env))->__jmpbuf)[JB_SP] = (unsigned) newthread->stack + STACKSIZE - sizeof(int);  
  ((*(newthread->env))->__jmpbuf)[JB_PC] = (unsigned) f;
  (*(newthread->env))->__mask_was_saved = 1;
  
  int new_id = tids.top();
  tids.pop();
  threads[new_id] = newthread;
  ready.push_back(new_id);
  
  set_mask(&set);          // switching to previous mask
  return new_id;	
}

the signal_handler

void dispatch(int sig){
  set_timer(QUANTUM);  //resetting the timer
  if (sig == CALL){    //specific call to dispatch
    if (ready.empty())
      error_handler(FATAL_THREAD_ERROR);
  }
  
  else {               //dispatch called by signal
    if (ready.empty())
      return;   // no ready threads, current keeps running		
  }
  
  int ready_tid = ready.front();
  ready.pop_front();
  
  if(setjmp(*(threads[running_thread]->env)) == 0){ // Save the running thread
    if (sig != CALL) {
      threads[running_thread]->state = READY; 
      ready.push_back(running_thread); 
    }
    
    running_thread = ready_tid;
    threads[running_thread]->state = RUN;
    threads[running_thread]->status.bursts++;
    longjmp(*(threads[running_thread]->env), 1); 
  }
}

I know it's a lot of code, but i'm desperate!!!

thanks!

[C_ntua]

First of all you call FREE twice on

FREE(*new_thread);
FREE(*new_thread);

that should be an error

[Eran]

fixed that one already, should be:

FREE((*new_thread)->env);

it never got there anyhow...

[Salem]

Why is your call to setjmp commented out?

[Eran]

sorry, part of the debugging process, its not the problem.