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Date: Mon, 10 Mar 2008 20:48:53 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Akinobu Mita <akinobu.mita@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] lib: introduce call_once()
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On Mon, 10 Mar 2008 23:57:05 +0900 Akinobu Mita <akinobu.mita@gmail.com> wrote:

> call_once() is an utility function which has similar functionality of
> pthread_once().
> 
> +/*
> + * call_once - call the initialization function only once
> + *
> + * @once_control: guarantee that the init_routine will be called only once
> + * @init_routine: initialization function
> + *
> + * The first call to call_once(), with a given once_control, shall call the
> + * init_routine with no arguments and return the value init_routine returned.
> + * If the init_routine returns zero which indicates the initialization
> + * succeeded, subsequent calls of call_once() with the same once_control shall
> + * not call the init_routine and return zero.
> + */
> +
> +static inline int call_once(struct once_control *once_control,
> +			    int (*init_rouine)(void))
> +{
> +	return likely(once_control->done) ? 0
> +			: call_once_slow(once_control, init_rouine);
> +}

I don't believe that this shold be described in terms of an "init_routine". 
This mechanism can be used for things other than initialisation routines.

It is spelled "routine", not "rouine".


Would it not be simpler and more general to do:

#define ONCE()						\
	({						\
		static long flag;			\
							\
		return !test_and_set_bit(0, flag);	\
	})

and then callers can do

	if (ONCE())
		do_something();

?