On 5/19/07, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote:
as a short demo of using a delayed work queue, i wrote the following
module which, every second, just does a printk() to /var/log/messages,
and stops when you unload it.
==========================================================================
#include <linux/module.h> // for all modules
#include <linux/init.h> // for entry/exit macros
#include <linux/kernel.h> // for printk macros
#include <linux/workqueue.h>
static void work_func(struct work_struct *unused);
static DECLARE_DELAYED_WORK(work, work_func);
static int count ;
static void
work_func(struct work_struct *unused)
{
printk(KERN_INFO "yee ha timer, %d.\n", ++count);
schedule_delayed_work(&work, HZ);
}
static int hi(void)
{
printk(KERN_INFO "Hello from timer.\n");
schedule_delayed_work(&work, HZ);
count = 0 ;
return 0;
}
static void bye(void)
{
printk(KERN_INFO "Goodbye from timer.\n");
cancel_delayed_work(&work);
flush_scheduled_work();
}
module_init(hi);
module_exit(bye);
MODULE_LICENSE("Dual BSD/GPL");
=======================================================================
the module works just fine, but i'm not sure if i'm closing down the
work queue properly upon module unloading. note that i'm doing both:
cancel_delayed_work(&work);
flush_scheduled_work();
is it necessary to do both? and i've seen code that is even more
careful to do:
if (!cancel_delayed_work(&work))
flush_scheduled_work();
just in case the work callback function is still running on return
from cancel_delayed_work().
Robert, i ran into this situation days back and i remember it worked
fine for me. But at the same time if you observe closely, value
returned by cancel_delayed_work(&work) is not checked at a lot of
places in the kernel, why i have no idea? Perhaps because it always
results in current work handler to complete(if it is in between).
Saying that i guess why would you need flush_scheduled_work() then?
Maybe you want to do a flush_workqueue() instead?
Just to add while inquiring i also came to know that return value from
queue_delayed_work() is also not checked at mostly all the places in
the kernel.Another big WHY??
And just to add as a bonus novice doubt even del_timer() 's return
value is not check at most of the places, another why??
Thoughts?
Thanks
--psr
what's the proper way to close this down? thanks.
rday
--
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA
http://fsdev.net/wiki/index.php?title=Main_Page
========================================================================
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