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SubjectRE: down_timeout
Date

I see this as the kind of function that should be implemented within the
semaphore interface itself. Very simple - Just wake me up when either 1) I
get the semaphore, or 2) I timed out.

A single implementation saves everyone from attempting to implement this
over and over and over.

Bob


-----Original Message-----
From: Ingo Oeser
[mailto:ingo.oeser@informatik.tu-chemnitz.de]
Sent: Wednesday, April 25, 2001 4:49 PM
To: Grover, Andrew
Cc: 'linux-kernel@vger.kernel.org'; Moore, Robert
Subject: Re: down_timeout

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>
<<<<<<<<<<<< been there and had much fun
>>>>>>>>>>>>

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