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>Queuing</H1
><P
> Placing yourself in the waitqueue is fairly complex, because you
must put yourself in the queue before checking the condition.
There is a macro to do this:
<TT
CLASS="FUNCTION"
>wait_event_interruptible()</TT
>
<TT
CLASS="FILENAME"
>include/linux/sched.h</TT
> The
first argument is the wait queue head, and the second is an
expression which is evaluated; the macro returns
<SPAN
CLASS="RETURNVALUE"
>0</SPAN
> when this expression is true, or
<SPAN
CLASS="RETURNVALUE"
>-ERESTARTSYS</SPAN
> if a signal is received.
The <TT
CLASS="FUNCTION"
>wait_event()</TT
> version ignores signals.
</P
><P
> Do not use the <TT
CLASS="FUNCTION"
>sleep_on()</TT
> function family -
it is very easy to accidentally introduce races; almost certainly
one of the <TT
CLASS="FUNCTION"
>wait_event()</TT
> family will do, or a
loop around <TT
CLASS="FUNCTION"
>schedule_timeout()</TT
>. If you choose
to loop around <TT
CLASS="FUNCTION"
>schedule_timeout()</TT
> remember
you must set the task state (with
<TT
CLASS="FUNCTION"
>set_current_state()</TT
>) on each iteration to avoid
busy-looping.
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