2007-02-13 22:41:21

by Chris Friesen

Subject: whatever happened to down_timeout()?

There has been some discussion on lkml about a function that would
either down a semaphore or else abort if it couldn't get the semaphore
in a certain amount of time. Something along the lines of:

down_timeout(struct semaphore *sem, long timeout);


Does something like this exist? Does anyone have a working
implementation? Does anyone see anything obviously wrong with the
following version (that I loosely based on one by Rupert Eibauer)?



semaphore.h:

extern int __down_timeout(struct semaphore * sem, unsigned int timeout);


/* "timeout" is the number of jiffies to wait.
* Returns -ETIME if timeout period expires.
*/
static inline int down_timeout(struct semaphore * sem, unsigned int timeout)
{
int ret = down_trylock(sem);
if (!ret)
ret = __down_timeout(sem, timeout);
return ret;
}




kernel/timer.c

int __down_timeout(struct semaphore * sem, int timeout)
{
int ret;
unsigned long expire;
struct timer_list timer;

expire = jiffies + timeout;
init_timer(&timer);
timer.expires = expire;
timer.data = (unsigned long) current;
timer.function = process_timeout;
add_timer(&timer);

ret = down_interruptible(sema);
if (ret && (jiffies > expire))
ret = -ETIME;
else
del_timer_sync(&timer);

return ret;
}


Thanks,
Chris

2007-02-13 23:44:57

by Chris Friesen

Subject: Re: whatever happened to down_timeout()?

Chris Friesen wrote:

> static inline int down_timeout(struct semaphore * sem, unsigned int
> timeout)
> {
> int ret = down_trylock(sem);
> if (!ret)
> ret = __down_timeout(sem, timeout);
> return ret;
> }

Sorry, I think that should be:

static inline int down_timeout(struct semaphore * sem, unsigned int timeout)
{
int ret = down_trylock(sem);
if (ret)
ret = __down_timeout(sem, timeout);
return ret;
}

Chris