Re: down_timeout

[Ingo Oeser]

On Wed, Apr 25, 2001 at 04:21:22PM -0700, Grover, Andrew wrote:
> It seems like we need to implement down_timeout (and
> down_timeout_interruptible) to fully flesh out the semaphore implementation.
> It is difficult and inefficient to emulate this using wrapper functions, as
> far as I can see.
> 
> Seems like this is a fairly standard interface to have for OS semaphores. We
> have a prototype implementation, and could contribute this, if desired.
> 
> Thoughts?

Sure you can't implement this via waitqueues? semaphores use them
internally anyway.

I use this for interrupt or polling based waiting:

/* IO polling waits */
/* Timeout after this amount of jiffies */
#define IO_POLL_TIMEOUT (HZ) 	
/* Split timeout while polling into chunks of that many jiffies */
#define IO_POLL_SPLIT 	2

/* generic interrupt based wait with timeouts! */
#define __wait_event_timeout_int(wq, condition, timeout, ret) \
	do { \
		struct wait_queue __wait; \
		signed long __expire=timeout; \
		__wait.task=current; \
		add_wait_queue(wq, &__wait); \
		for (;;) { \
			current->state=TASK_UNINTERRUPTIBLE; \
			mb(); \
			if (condition) break; \
			__expire=schedule_timeout(__expire); \
			if (__expire == 0) {  \
				ret=-ETIMEDOUT; \
				break; \
			} \
		} \
		current->state = TASK_RUNNING; \
		remove_wait_queue(wq, &__wait); \
	} while (0)

/* polling wait, if we shouldn't use interrupts for this */
#define __wait_event_timeout_poll(wq, condition, timeout, ret) \
	do { \
		unsigned int __tries=0; \
		unsigned int __maxtry=timeout / IO_POLL_SPLIT; \
		do { \
			schedule_timeout(IO_POLL_SPLIT); \
			if (condition) \
				break; \
		} while (++__tries < __maxtry); \
		if (__tries == __maxtry && !condition) \
			ret=-ETIMEDOUT; \
	} while (0)
	
#ifdef INTS_ARE_CHEAP
#define __wait_event_timeout(wq, condition, timeout, ret) \
	__wait_event_timeout_int(wq, condition, timeout, ret)
#else /* INTS_ARE_CHEAP */
#define __wait_event_timeout(wq, condition, timeout, ret) \
	__wait_event_timeout_poll(wq, condition, timeout, ret)
#endif /* INTS_ARE_CHEAP */

#define wait_event_timeout(wq, condition, timeout, ret)	\
	do { \
		if (condition) \
			break; \
		__wait_event_timeout(wq, condition, timeout, ret); \
	} while (0)

What about that?

Use it just as you use wait_event() but check for -ETIMEDOUT as
value in ret.

Regards

Ingo Oeser
-- 
10.+11.03.2001 - 3. Chemnitzer LinuxTag <http://www.tu-chemnitz.de/linux/tag>
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