Thread: seg fault on pthread_mutex_init

Hi people!!

I know this is short notice, but I've had this segmentation fault on a pthread_mutex_init (I'm almot 100% that's where it is), and I can't figure out why.

in a header.h, I have

Code:

typedef struct thread {
  pthread_mutex_t lock;
  int state;
  int remaining_time;
  struct thread * next;
} thread_data;

thread_data *OpSys,
	    *user1, *user2, *user3, *user4, *user5,
	    *MMU_data;

in my main, I have

Code:

  pthread_mutex_init(OpSys->lock, NULL);
  pthread_mutex_init(&user1->lock, NULL);
  pthread_mutex_lock(&user1->lock);
  pthread_mutex_init(&user2->lock, NULL);
  pthread_mutex_lock(&user2->lock);
  pthread_mutex_init(&user3->lock, NULL);
  pthread_mutex_lock(&user3->lock);
  pthread_mutex_init(&user4->lock, NULL);
  pthread_mutex_lock(&user4->lock);
  pthread_mutex_init(&user5->lock, NULL);
  pthread_mutex_lock(&user5->lock);
  pthread_mutex_init(&MMU_data->lock, NULL);
  pthread_mutex_lock(&MMU_data->lock);

somewhere in that mess I get the seg fault... I'm not too good with pointers, and even though it compiles fine, I can't obviously run that.

Any suggestions???

Thanks

oopsy... yes, there's an ampersand missing, and it's not voluntary

Can we assume that you have allocated memory to go with all those thread_data pointers?

what do you mean?

I did allocate the memory... didn't I?
ah crap.. no I didn't!!
---------------------------------------------
Now, I did the memory allocation

Code:

thread_data *OpSys;
OpSys = (thread_data *) malloc (sizeof(thread_data));

but that gives me a "conflicting type for OpSys", "previous declaration of OpSys", and "warning: initilization makes integer from pointer without a cast"... :-/

> a "conflicting type for OpSys", "previous declaration of OpSys"
You've got two of them, and they don't agree

> "warning: initilization makes integer from pointer without a cast"
Makes no sense given that line of code
The usual problem is makes pointer from int cast, and that's because you didn't include stdlib.h for malloc

Don't forget to malloc your user1 to 5 (why isn't this an array of users)

pthread_mutex_init(OpSys->lock, NULL);
pthread_mutex_init(&user1->lock, NULL);
One of these needs an &
or the other one doesn't need an &

> a "conflicting type for OpSys", "previous declaration of OpSys"
You've got two of them, and they don't agree

I have it declared once and only once. This error didn't come up before I wrote in the maloc part, that's why I'm confused

> "warning: initilization makes integer from pointer without a cast"
Makes no sense given that line of code
The usual problem is makes pointer from int cast, and that's because you didn't include stdlib.h for malloc

Don't forget to malloc your user1 to 5 (why isn't this an array of users)

stdlib.h is in there and has been...

pthread_mutex_init(OpSys->lock, NULL);
pthread_mutex_init(&user1->lock, NULL);
One of these needs an &
or the other one doesn't need an &

yep... I just forgot that, but it's in too now!

By the way, the malloc is done in header.h, not in main. Is that a problem?

No idea - post a short and complete program which demonstates the problem

Salem,
so basically, what we have to do is simulates an operating system, that created five user thread and a memory management unit (i'm not even here yet)
We have to implement a round robin schedule. Each thread is put in running state after the other.

my header file has the structs

Code:

/* Struct for thread's info */
typedef struct thread {
  pthread_mutex_t lock;
  int state;
  int remaining_time;
  struct thread * next;
} thread_data;

typedef struct {
  thread_data * head;
} queue;

queue * qp;

thread_data * OpSys,
	    * user[USERS],
	    * MMU_data;

in my main (i switched the memory allocation by the way from the header to main)

Code:

int main (void) {

  int i;

  OpSys = (thread_data *) malloc (sizeof(thread_data));
  MMU_data = (thread_data *) malloc (sizeof(thread_data));
  for (i=0; i<USERS; i++)
    user[i] = (thread_data *) malloc (sizeof (thread_data));

  /* initializes all mutex and set them to lock (except OS one) */
  pthread_mutex_init(&OpSys->lock, NULL);
  pthread_mutex_init(&MMU_data->lock, NULL);
  pthread_mutex_lock(&MMU_data->lock);
  for (i=0; i<USERS; i++) {
    pthread_mutex_init(&user[i]->lock, NULL);
    pthread_mutex_lock(&user[i]->lock);
  }

  /* initialize queue */
  insert();

  /* all states are set to NOT DONE (0) */
  OpSys->state = MMU_data->state = NOT_DONE;
  for (i=0; i<USERS; i++)
    user[i] = NOT_DONE;

  create_t (OS_thread, OS);

  pthread_join (OS_thread, NULL);
  return;
} /* end of main() */

I've fixed all the errors, and the program compiles again

PS: I switched to an array for my users... yep, that makes it a lot clearer and shorter!! ;-)

Well now is the time to compile it with debug
say
gcc -ggdb prog.c

and use the debugger to catch the line where the segfault happens

Like
gdb a.out
run

well, the seg fault is gone... but it's not working correctly! I'm gonna go bang my head on the wall for a while. Doubt that'll help, but who knows

Code:

  /* all states are set to NOT DONE (0) */
  OpSys->state = MMU_data->state = NOT_DONE;
  for (i=0; i<USERS; i++)
    user[i]->state = NOT_DONE; /* perhaps? */

Thanks Dave for catching that...

That doesn't begin to solve what doesn't work with that damn program!!!