On 12/06/2012 02:19 AM, David Bryant wrote:
> statement-expression would also work. Are we conflating separate ideas -
> the idea of user conditions and the idea of setup/cleanup?
FWIW, tracepoint_cond could be implemented as loan pattern (in pseudocode):
with_tp( provider, name, REF ) {
if (cond) {
// pre emit code block
...
emit_REF( arg0, ... );
// post emit code block
...
}
}
This could even be nested. E.g.
with_tp( provider1, nameA, REF1 ) {
with_tp( provider2, nameB, REF2 ) {
if (cond) {
// pre emit code block if both are enabled
...
emit_REF1( arg0x, ... );
emit_REF2( arg0y, ... );
// post emit code block if both are enabled
...
}
}
}
Nesting would be rather unpleasant with the proposed
tracepoint_cond(provider, name, pre, post, ...).
--
Paul
>
>> While we are there, it would be good to make the "pre" handler test a
>> condition. For your use-case, you would just have to pass a pre :
>>
>> { printf("pre\n"); a = malloc(16); 1; }
>>
>> So we could do:
>>
>> if (pre)
>> __tracepoint_cb_##provider##___##name(__VA_ARGS__);
>> (post)
>>
>> and therefore support not only to setup something, but also to add an
>> extra check on whether tracing should be skipped or not. If someone
>> passes "1" as end of the compound statement, it will always evaluate to
>> 1, and therefore the compiler will remove any extra branch in -O2.
>>
>> One question stands though: how would we integrate this with sdt.h
>> STAP_PROVEV() ?
> I'm yet to look at this.
>
> Thanks,
> Dave
>
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