Is not changing the state to TASK_INTERRUPTIBLE before calling schedule() renders it not-schedulable? I thought task would be removed off run-queue by schedule() because it is in TASK_INTERRUPTIBLE state.

I was making a sort of task queue. Threads puts themselves into this queue when a resource(say memory-space) is not available. And other thread, post releasing the memory space, will wake the first thread in queue.

There are other means to achieve that, but I wondered why the above mentioned method did not succeed in making thread sleep.

On Wed, Jun 11, 2014 at 11:21 PM, <Valdis.Kletnieks@vt.edu> wrote:

On Wed, 11 Jun 2014 23:09:05 +0530, Joshi said:

> set_current_state (TASK_INTERRUPTIBLE);
> schedule ();
>
> Is this a sure-shot way of putting a thread to sleep, or are there
> conditions when this may not put the calling thread into sleep?

This will only succeed in guaranteeing the thread sleep if the thread has done
something *else* to render it not schedulable. schedule() will
return right back to that thread if it's the highest-priority thing
that's runnable.

What problem are you trying to solve? Usually, you do that sort of
schedule() when you're doing something that will take a relatively long
chunk of time, and want other things to have a *chance* of running. But
usually, you're perfectly happy with continuing to run if nobody else
wants to run.

Why did you want a guaranteed sleep? If it's because you've started an
I/O and you *know* it will be 125 milliseconds before you can make further
progress, there's mdelay() and similar APIs... and so on for other reasons
for wanting to sleep (for instance, blocking on a lock has an API, etc)

--
Joshi