<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Dec 12, 2019, at 5:58 AM, Sam McCall via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Short version: clangd would like to be able to build a client+server that can make RPCs across the internet. An RPC system isn't a trivial dependency and rolling our own from scratch isn't appealing.<div class="">Have other projects had a need for this? Any advice on how to approach such dependencies?</div><div class=""><br class=""></div><div class="">--</div><div class=""><br class=""></div><div class="">Longer: clangd (a language server, like an IDE backend) builds an index of the project you're working on in order to answer queries (go to definition, code completion...). This takes *lots* of CPU-time to build, and RAM to serve.</div><div class="">For large codebases with many developers, <a href="https://llvm.discourse.group/t/sharing-indexes-for-multiple-users/202" class="">sharing an index across users</a> is a better approach - you spend the CPU in one place, you spend the RAM in a few places, and an RPC is fast enough even for code completion. We have experience with this approach inside Google.</div><div class=""><br class=""></div><div class="">We'd like to build this index server upstream (just a shell around clangd's current index code) and put the client in clangd. For open-source projects, I imagine the server being publicly accessible over the internet.<br class=""></div><div class="">This means we care about</div><div class=""> - latency (this is interactive, every 10ms counts)</div><div class=""> - security</div><div class=""> - proxy traversal, probably</div><div class=""> - sensible behavior under load</div><div class=""> - auth is probably nice-to-have</div><div class=""><br class=""></div><div class="">I don't think this is something we want to build from scratch, I hear portable networking is hard :-)</div></div></div></blockquote><div><br class=""></div><div>It really isn't that bad. Just as a note, LLDB does have portable socket communication already, so it could be a refactor and reuse exercise rather than building from scratch.</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="">The most obvious thing is to depend on something like Thrift, grpc, etc, but these aren't trivial dependencies to take on. They could probably be structured as an optional CMake dependency, which we'd want to ask distributors to enable.</div></div></div></blockquote><div><br class=""></div><div>This is possible, but adding large and non-standard external dependencies have significant drawbacks for distribution.</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><br class=""></div><div class="">Have other projects had anything like these requirements? Any solutions, or desire to use such infrastructure? I saw some RPC layer in ORC, but it seems mostly abstract/FD-based IPC.</div></div></div></blockquote><div><br class=""></div><div>The ORC RPC layer in-tree runs over sockets, but I've implemented it to run over XPC (a Darwin low-latency IPC mechanism). It is actually a really useful abstraction over true remote procedure calls. </div><div><br class=""></div><div>-Chris</div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><br class=""></div></div>
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