blocks: vector_sink reserve (min) data length in constructor

[noc0lour]

In the vector_sink block data is allocated dynamically on every call. To improve performance a user could supply a minimum number of items he plans to stream into the vector sink, so memory is already allocated. Could improve speed during testing as well.

[marcusmueller]

Idea: Make vector_sink have a "total number of items to store": Vector sink is in most cases used directly after a head block, and that's very a) annoying, b) a copying of perfectly fine samples and c) would be an excellent size to allocate first.

[noc0lour]

So, basically have a max_num_items ?

[lshariprasad]

Hi, I'm Hari Prasad L S, a GSoC 2026 applicant. I'd like to work on this issue and plan to submit a PR within 5 days.

[marcusmueller]

Hi @lshariprasad, I'm afraid we forgot to close this issue after merging the feature (see the linked PR above).

So, there's nothing to do here.

Generally, you not seeing the feature yet means you haven't checked out the Vector Sink e.g. in GNU Radio companion. If that's because you're not already quite familiar with GNU Radio: Friendly reminder to get comfortable with the software before opening Pull Requests for it!