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Thank you. Your comments help me so much.
It seems to solve my question between completion and semaphore.

Have a nice day.



On 5/19/06, Arjan van de Ven <arjan@infradead.org> wrote:
quoted text
>
> On Fri, 2006-05-19 at 12:41 +0900, minchan Kim wrote:
> > Thanks to your commenting.
> >
> > I understand your point.  But I see the book "Understanding of the
> > Linux Kernel", it says "Semaphore happen race condition problem in the
> > SMP envirioment since call up and down concurrency. But Completion
> > isn't"
> >
> > I don't understand it. Do you understand it?
>
> I think they mean that semaphores will cause exclusion (but really, use
> mutexes, much easier and they are replacing semaphores), while
> completions do not cause exclusion...
>
> eg you can use a mutex to prevent concurrent access (as the code snippet
> I gave you before shows), while a completion really doesn't do that.
> The book too artifically tries to tie these concepts together by trying
> to explain the difference in a micro scale, but that's wrong.
> They are ENTIRELY different things. Not even comparable. So saying
> "they're different in <this tiny detail>" sort of implies they're
> similar constructs in many other ways. They are not. Don't even think
> they are.
>
> (having said that, some people used to abuse semaphores to do a
> completion type of behavior, which is where the confusion is coming
> from, but just don't do that or even focus on that, it's like using the
> back of a book to drive a nail in the wall and then ask "what's the
> difference between a book and a hammer since I now have both". The
> answer is "who cares. Just use the hammer for your own sanity" :)
>
>
>

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<div>Thank you. Your comments help me so much. </div>
<div>It seems to solve my question between completion and semaphore. </div>
<div>&nbsp;</div>
<div>Have a nice day.</div>
<div><br><br>&nbsp;</div>
<div><span class=3D"gmail_quote">On 5/19/06, <b class=3D"gmail_sendername">=
Arjan van de Ven</b> &lt;<a href=3D"mailto:arjan@infradead.org">arjan@infra=
dead.org</a>&gt; wrote:</span>
<blockquote class=3D"gmail_quote" style=3D"PADDING-LEFT: 1ex; MARGIN: 0px 0=
px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">On Fri, 2006-05-19 at 12:41 +090=
0, minchan Kim wrote:<br>&gt; Thanks to your commenting.<br>&gt;<br>&gt; I =
understand your point.&nbsp;&nbsp;But I see the book &quot;Understanding of=
 the
<br>&gt; Linux Kernel&quot;, it says &quot;Semaphore happen race condition =
problem in the<br>&gt; SMP envirioment since call up and down concurrency. =
But Completion<br>&gt; isn't&quot;<br>&gt;<br>&gt; I don't understand it. D=
o you understand it?
<br><br>I think they mean that semaphores will cause exclusion (but really,=
 use<br>mutexes, much easier and they are replacing semaphores), while<br>c=
ompletions do not cause exclusion...<br><br>eg you can use a mutex to preve=
nt concurrent access (as the code snippet
<br>I gave you before shows), while a completion really doesn't do that.<br=
quoted text
>The book too artifically tries to tie these concepts together by trying<br=
>to explain the difference in a micro scale, but that's wrong.<br>They are =
ENTIRELY different things. Not even comparable. So saying
<br>&quot;they're different in &lt;this tiny detail&gt;&quot; sort of impli=
es they're<br>similar constructs in many other ways. They are not. Don't ev=
en think<br>they are.<br><br>(having said that, some people used to abuse s=
emaphores to do a
<br>completion type of behavior, which is where the confusion is coming<br>=
from, but just don't do that or even focus on that, it's like using the<br>=
back of a book to drive a nail in the wall and then ask &quot;what's the
<br>difference between a book and a hammer since I now have both&quot;. The=
<br>answer is &quot;who cares. Just use the hammer for your own sanity&quot=
; :)<br><br><br></blockquote></div><br>

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