[RFC] Fwd: Re: Fwd: Linux Kernel: down_timeout

Rupert Eibauer (Rupert@ces.ch)
Thu, 15 Aug 2002 11:57:17 +0200


Please reply to me directly, I am not
subscribed to the lkml.

---------- Forwarded Message ----------

Subject: Re: Fwd: Linux Kernel: down_timeout
Date: Thu, 15 Aug 2002 10:44:55 +0100 (BST)
From: Matthew Kirkwood <matthew@hairy.beasts.org>
To: Rupert Eibauer <Rupert@ces.ch>

On Thu, 15 Aug 2002, Rupert Eibauer wrote:
> I found your thread
> [PATCH][RFC] Lightweight user-level semaphores
> (jan 2002)
> later, so please read on..

I'm no kernel guru, but this looks really useful. You
should probably send it to the linux-kernel list and to
Rusty Russel -- it would be a particularly useful extra
feature for his futexes.

Cheers,
Matthew.

> ---------- Forwarded Message ----------
>
> Subject: Linux Kernel: down_timeout
> Date: Thu, 15 Aug 2002 11:14:24 +0200
> From: Rupert Eibauer <Rupert@ces.ch>
> To: andrew.grover@intel.com, ingo.oeser@informatik.tu-chemnitz.de,
> robert.moore@intel.com
>
> Hi,
>
> I found your thread (Apr 2001) about down_timeout on the lkml.
> down_timeout is needed more often then you might think.
>
> Does anybody of you know why it hasnt been implemented in
> the kernel until now?
>
> My version of down_timeout is attached below.
>
>
> waiting for your answer,
>
> Rupert
>
>

---------- End of Forwarded Message ----------

Here is the header snippet:
-8<--------------------------------------------------------------------------
extern int __down_timeout(struct semaphore * sem, int timeout);

extern inline int down_timeout(struct semaphore * sem, int timeout)
{
int ret = 0;
if (atomic_dec_if_positive(&sem->count) < 0)
ret = __down_timeout(sem, timeout);
smp_wmb();
return ret;
}
-8<--------------------------------------------------------------------------

This is for the .c file:
-8<--------------------------------------------------------------------------
static void process_sema_timeout(unsigned long data) {
struct task_struct *p = (struct task_struct *)data;

wake_up_process(p);
}

extern int __down_timeout(struct semaphore * sem, int timeout)
{
int ret = 0;
unsigned long expire;
struct timer_list timer;

if (timeout > 0) {

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

if (ret = __down_interruptible(sema)) {
/* check whether the timeout woke us up */
if (jiffies > expire)
ret = -ETIME;
else
del_timer_sync(&timer);
} else
del_timer_sync(&timer);

} else if (timeout == 0) { // timeout=0 means now
/* our caller (inline int down_timeout) already tried to
get the semaphore _now_ and it failed ! */
ret = !0;
} else { // timeout<0 means wait forever
ret = __down_interruptible(sema)
}
return ret;
}
-8<--------------------------------------------------------------------------

-- 
+-----------------------------------------------------------------------------+
| CCCC EEEE SSSS  Creative Electronic Systems | Rupert Eibauer                |
| C    E    S     38 av. Eugene Lance         | Linux Kernel Hacker           |
| C    EEE  SSSS  PO Box 584                  |                               |
| C    E       S  CH-1212 Grand-Lancy 1       |                               |
| CCCC EEEE SSSS  Switzerland                 | email: rupert@ces.ch          |
+-----------------------------------------------------------------------------+
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/