Re: lock_kernel

[Ralph Corderoy <ralph@inputplus.demon.co.uk>]

Hi Siva,

> when the macro lock_kernel is defined as 
> do{ } while(0)
> and when it comes 'out' immediately('cos the condition is false by
> having specified 0) from the flow of control what is the rational
> behind using it?

I don't know the macro but

    while (0) {
        /* never executed. */
    }

and

    do {
        /* executed once. */
    } while (0);

should make things clearer.  That is, you're wrong when you say `it
comes 'out' immediately'.  It doesn't, but executes exactly once as a
do...while loop tests the condition at the end of the iteration.

    /* a while-loop. */
    loop:
        if (cond) {
            /* body of loop. */
            goto loop;
        }

    /* a do-while-loop. */
    loop:
        /* body of loop. */
        if (cond) {
            goto loop;
        }

Read K&R2 for more details.


Ralph.

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