Hello,
The conditional "trick" of:
condition ? printf(...) : 1;
(where condition is an inline known at compile-time) is extensively used in the
DTrace ToolKit (see for example dapptrace).
Now, as far as I have been able to find, this is explicitly documented as
impossible: "The second and third expressions [of the conditional] also may not
invoke a tracing function such as trace or printf.", as seen in
https://docs.oracle.com/cd/E23824_01/html/E22973/typopexp.html#glgdp . Also I
have seen some threads back in the list, around 2009, discussing if/then/else
alternatives, but this construction doesn't seem to have been mentioned.
I'd guess that it's working because of the compile-time inline being treated as
a constant and compiled away. But... is that it / is that all? Or am I missing
something?
Also, this style of conditional execution is much more compact than using
predicates and small action blocks. Should I consider any disadvantage?
Performance maybe?
And speaking of performance: I've read about cacheable predicates in the Oracle
guide and about clausule and thread variables vs globals and arrays. Is there
anything else to be aware of? Or, any way in which I could check myself the
performance characteristics of my DTrace programs - as in the case of the
conditional "trick" vs multiple predicate/action blocks?
--- Horacio
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