How to sleep and wake a thread??? Post: 302582512

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Top Forums Programming How to sleep and wake a thread??? Post 302582512 by gabam on Friday 16th of December 2011 08:23:16 AM

12-16-2011

Registered User

How to sleep and wake a thread???

Hi guys,
I am creating two posix threads. I have some queries, hopefully you will help me out with them
1) How can I put a thread to indefinite sleep, for indefinite time period. I am familiar with this

Code:

sleep(5);

for 5 second, how can I make it indefinite??
2) How can one thread wake another sleeping thread
3) Can one thread force another thread to go to sleep

Here is the program which is really bothering me, the idea is to have two threads, one filling the stack, and one emptying it. But I can't have one of my thread to wake up the other, after the stack is empty or full
See it for yourself!

Code:

 
#include <stdio.h>
#include <stdlib.h>
#include <curses.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#define MAX_SIZE 10
int Counter;
struct Stack
{
 int home[MAX_SIZE];
 int top;
};
struct Stack s;
void InitStack(struct Stack *s)
{
 s->top = -1;
 Counter = 0;
}
void Push(struct Stack *s, int x)
{
 if(s->top == MAX_SIZE-1)
 {
  printf("Stack is full!\n");
  exit(0);
 }
 else
 s->top++;
 s->home[s->top] = x;
 Counter++;
 printf("Counter = %d\n", Counter);
}
void Pop(struct Stack *s)
{
 int y;
 if(s->top == -1)
 {
  printf("Stack empty!\n");
  exit(0);
 }
 else
 y = s->home[s->top];
 s->top--;
 printf("%d poped\n",y);
 Counter--;
 printf("Counter = %d\n", Counter);
}

void *threadA(void *);
void *threadB(void *);
int main()
{
 InitStack(&s); 
 int i, j, k;
 pthread_t tid[2];
 pthread_attr_t attr[2];
 for(i=1;i<=2;i++)
 {
  pthread_attr_init(&attr[i-1]);
 }
  {
  pthread_create(&tid[0],&attr[0],threadA,(void *)786);
  pthread_create(&tid[1],&attr[1],threadB,(void *)786);
  }
 { 
 pthread_join(tid[0],NULL);
 pthread_join(tid[1],NULL);
 }
return 0;
}

void *threadA(void *n)
{
 int x;
 x = (int)n;
 while(1) 
 {
 if(Counter != MAX_SIZE)
 {
 Push(&s,x);
 printf("x = %d\n", x);
 sleep(1);
 }
 else
 {
 printf("Going for a long sleep as Stack is full!\n");
 sleep(50);
 }
 }
}
void *threadB(void *n)
{
 int x;
 sleep(15);
 while(1)
 {
 if(Counter != 0)
 {
 Pop(&s);
 sleep(1);
 }
 else
 {
 printf("Going for a long sleep as Stack is empty!\n");
 sleep(50);
 }
 }
}

If you can explain your points with a very small program, that would be so so nice of you.
Desperately waiting for your wonderful replies!!!!

Thanks alot in advance!

Last edited by gabam; 12-16-2011 at 10:18 AM..

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thr_suspend

thr_suspend(3C) 					   Standard C Library Functions 					   thr_suspend(3C)

NAME

       thr_suspend, thr_continue - suspend or continue thread execution

SYNOPSIS

       cc -mt [ flag... ] file...[ library... ]
       #include <thread.h>

       int thr_suspend(thread_t target_thread);

       int thr_continue(thread_t target_thread);

DESCRIPTION

       The  thr_suspend() function immediately suspends the execution of the thread specified by target_thread. On successful return from thr_sus-
       pend(), the suspended thread is no longer executing. Once a thread is suspended, subsequent calls to thr_suspend() have no effect.

       The thr_continue() function resumes the execution of a suspended thread. Once a suspended thread is continued, subsequent calls to thr_con-
       tinue() have no effect.

       A  suspended  thread  will  not	be  awakened  by any mechanism other than a call to thr_continue().  Signals and the effect of calls tomu-
       tex_unlock(3C), rw_unlock(3C), sema_post(3C), cond_signal(3C), and cond_broadcast(3C) remain pending until the execution of the	thread	is
       resumed by thr_continue().

RETURN VALUES

       If successful, the thr_suspend() and thr_continue() functions return  0. Otherwise, a non-zero value is returned to indicate the error.

ERRORS

       The thr_suspend() and thr_continue() functions will fail if:

       ESRCH	       The target_thread cannot be found in the current process.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       thr_create(3C), thr_join(3C), attributes(5), standards(5)

WARNINGS

       The  thr_suspend()  function  is  extremely  difficult  to  use safely because it suspends the target thread with no concern for the target
       thread's state. The target thread could be holding locks, waiting for a lock, or waiting on a condition variable when it is unconditionally
       suspended.   The  thread  will  not  run  until	thr_continue()	is  applied,  regardless of any calls to mutex_unlock(), cond_signal(), or
       cond_broadcast() by other threads. Its existence on a sleep queue can interfere with the waking up of other threads that are  on  the  same
       sleep queue.

       The  thr_suspend()  and thr_continue() functions should be avoided. Mechanisms that involve the cooperation of the targeted thread, such as
       mutex locks and condition variables, should be employed instead.

SunOS 5.10							    22 Mar 2002 						   thr_suspend(3C)