Re: Add tags without copying samples?

[Marcus Müller]

Forgot to add: propagating tags from all inputs to the output is the default tag 
propagation policy, so B has to do essentially nothing if it doesn't itself care for the 
tags.	


On 25.02.22 21:55, Marcus Müller wrote:
> Hi Thomas,
>
> sadly, within the GNU Radio 3.x framework, this isn't possible.
>
> There's one possible "lower effort" solution. Assume you have this
>
>
> Source -> A -> B -> Sink
>
> where A is the block that currently needs to copy items just to add tags.
>
> We can now do
>
> Source ------> B -> Sink
>         \-> A -/^
>
> where B is doing some functionality that you needed anyway. Now, B just gets a second 
> input, that it completely ignores – except for the tags.
>
> A gets modified in that it doesn't copy the input, but simply says "hey, I produced 
> items", without actually producing items; B would ignore them anyways. A, however, adds 
> the tags.
>
> Not quite sure this helps you much...
>
> Best regards,
> Marcus
>
> On 25.02.22 17:36, Thomas Lorblanchès wrote:
> > Hi all,
> > I have some custom blocks that do not change the samples but only add tags in the output 
> > stream.
> > At very high sampling rates, all these "memcpy" operations to copy the input samples to 
> > the output stream take a lot of time and put a lot of memory pressure on the system, and 
> > are completly useless on an algorithmic point of view.
> > Is there a clever way to add tags without copying the samples?
> > Thanks for your answers.
> > Thomas