dtrace discuss - Feb 2008 - Initialisation of thread local vars

If I understand the docs correctly the only way to initialize self vars is
automatic initialization: zero it is.

I feel it would be very nice if we could explicitly initialize vars before their
use. To values not zero that is.  Currently I have a situation where the
application uses just positive values. zero is a valid value here that therefore
cannot be used to mean "uninitialized".
I now need another self-> var telling me if the actual variable is
initialized. This flag is set always when that other var is set. And needs
always be used in the predicates to tests if that var has meaningful
information.
Using the value -1 only once would make the code more readable.

Is this auto init of thread local variables there to stay (design?) or could it
be an enhancement for a future version of DTrace?


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This message posted from opensolaris.org

What''s wrong with initializing those variables in the dtrace:::BEGIN
probe? It''s guaranteed to run first, after all...

Cheers
  -- perry


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This message posted from opensolaris.org

Never mind, I mis-read your question.

Perhaps we should have a dtrace:::BEGIN-self probe that runs once for each
thread?

Cheers
  -- perry


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This message posted from opensolaris.org

Hi Paul,

It''s not possible to set a value other than zero to be used as the  
default value for a variable. The use of zero as the default value is  
tied to how variables are allocated and freed internally. The  
initialization of new thread-local variables to zero is fairly baked  
into the design of DTrace and while it might seem suboptimal to  
require two variables in the case you described, that''s how
you''ll
have to do it.

Adam

On Feb 18, 2008, at 5:24 AM, Paul van den Bogaard wrote:
> If I understand the docs correctly the only way to initialize self  
> vars is automatic initialization: zero it is.
>
> I feel it would be very nice if we could explicitly initialize vars  
> before their use. To values not zero that is.  Currently I have a  
> situation where the application uses just positive values. zero is a  
> valid value here that therefore cannot be used to mean  
> "uninitialized".
> I now need another self-> var telling me if the actual variable is  
> initialized. This flag is set always when that other var is set. And  
> needs always be used in the predicates to tests if that var has  
> meaningful information.
> Using the value -1 only once would make the code more readable.
>
> Is this auto init of thread local variables there to stay (design?)  
> or could it be an enhancement for a future version of DTrace?
>
>
> --
> This message posted from opensolaris.org
> _______________________________________________
> dtrace-discuss mailing list
> dtrace-discuss at opensolaris.org

--
Adam Leventhal, Fishworks                        http://blogs.sun.com/ahl