[PATCH] D93531: [clangd] Reuse buffer for JSONTransport::readRawMessage

Fri Dec 18 07:32:17 PST 2020

njames93 added a comment.

In D93531#2463052 <https://reviews.llvm.org/D93531#2463052>, @sammccall wrote:

> This adds a bit of complexity, making the code here a fair amount harder to follow and verify the correctness of.
>
> - Do we have evidence that these allocations are causing a problem? (e.g. do we observe a significant decrease in RSS after the patch)? Naively I would expect these allocations to be basically unimportant compared to those of the JSON objects themselves.(And I don't particularly expect either of them to be significant - the comment on the other review was really just "0 probably isn't the right arg to  malloc_trim if there's any allocation going on").

It's not causing problems per say. but given the incoming json messages can contain a whole file plus things like escape chars. its wise to allocate a buffer that will grow to the largest json it receives but never shrink.

> - there seem to be simpler ways to structure this avoiding allocations. JSONLineBuffer is effectively statically bounded, and can be `SmallString<32>` or so. The content buffer could simply be passed in if I'm reading right: `bool readRawMessage(std::string&)`? OutputBuffer probably does need to be a member variable though.

Its not statically bounded unfortunately, the length is how ever long a line in the json is, which can be infinite. the read line function uses a buffer size of 1024 as an upperbound.
However that can easily be exceeded as I think the contents of files are escaped so they will be read as 1 long line. It may be slightly more readable to make the function take a reference to the buffer though.

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https://reviews.llvm.org/D93531