Messages in this thread |  | | | Date | Sun, 23 Mar 2008 03:30:10 -0400 | | From | Chris Snook <> | | Subject | Re: Question about C language. | |
Francis Moreau wrote:
> Hello,
>
> I know it's a bit out of topic but this is something I need to clarify for
> writing a Linux driver... hope you don't mind.
>
> In my driver I have a global variable that controls a loop such as:
>
> int my_condition;
>
> void change_my_condition(int new)
> {
> my_condition = new;
> }
>
> int foo(void)
> {
> /* irqs are disabled */
> my_condition = 1;
> do {
> ....
> local_irq_enable();
> cpu_sleep();
> local_irq_disable();
>
> } while (my_condition);
>
> }
>
> This variable is modified by an interrupt handler define in another file
> by using 'change_my_condition' function.
>
> By reading the ISO C99 specification, I _think_ that I needn't any
> kind of barrier
> or even use the volatile type qualifier for my_condition variable to make a true
> access to 'my_condition' in the controlling expression of the while, but I'm not
> sure.
>
> Coud anybody confirm ?
>
> Thanks,
Even volatile may be insufficient with some architecture/compiler
combinations. You should use explicit barriers wherever you need them,
or Bad Things will happen.
-- Chris
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