internal/lsp/cache: optimize Snapshot.clone

This change replaces the single large map used for snapshot.goFiles
by a map of 256 stripes, each of which becomes immutable once shared.
This optimizes the common case in which the copy is nearly identical
to the original.

We still need to visit each map entry to see whether it needs to be
deleted (which is rare) and to inherit the handle in the usual case.
This is now done concurrently.

Also, share the (logically immutable) []PackageIDs slices across
old and new snapshots. This was worth 5% of CPU and 1/3 of allocations
(all small).

Benchmark on darwin/arm64 shows a 29% reduction for DidChange.

$ go test -v ./gopls/internal/regtest/bench -run=TestBenchmarkDidChange -didchange_dir=$HOME/w/kubernetes -didchange_file=pkg/util/hash/hash.go

Before:
BenchmarkStatistics	     100	  22955469 ns/op	11308095 B/op	   47412 allocs/op
BenchmarkStatistics	     100	  23454630 ns/op	11226742 B/op	   46882 allocs/op
BenchmarkStatistics	     100	  23618532 ns/op	11258619 B/op	   47068 allocs/op

After goFilesMap:
BenchmarkStatistics	     100	  16643972 ns/op	 8770787 B/op	   46238 allocs/op
BenchmarkStatistics	     100	  17805864 ns/op	 8862926 B/op	   46762 allocs/op
BenchmarkStatistics	     100	  18618255 ns/op	 9308864 B/op	   49776 allocs/op

After goFilesMap and ids sharing:
BenchmarkStatistics          100          16703623 ns/op         8772626 B/op      33812 allocs/op
BenchmarkStatistics          100          16927378 ns/op         8529491 B/op      32328 allocs/op
BenchmarkStatistics          100          16632762 ns/op         8557533 B/op      32497 allocs/op

Also:
- Add comments documenting findings of profiling.
- preallocate slice for knownSubdirs.
- remove unwanted loop over slice in Generation.Inherit

Updates golang/go#45686

Change-Id: Id953699191b8404cf36ba3a7ab9cd78b1d19c0a2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/410176
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Alan Donovan <adonovan@google.com>
7 files changed
tree: e10425bb95fb624efa19d5398108494c5786ba1e
  1. benchmark/
  2. blog/
  3. cmd/
  4. container/
  5. copyright/
  6. cover/
  7. go/
  8. godoc/
  9. gopls/
  10. imports/
  11. internal/
  12. playground/
  13. present/
  14. refactor/
  15. txtar/
  16. .gitattributes
  17. .gitignore
  18. .prettierrc
  19. AUTHORS
  20. codereview.cfg
  21. CONTRIBUTING.md
  22. CONTRIBUTORS
  23. go.mod
  24. go.sum
  25. LICENSE
  26. PATENTS
  27. README.md
README.md

Go Tools

PkgGoDev

This repository provides the golang.org/x/tools module, comprising various tools and packages mostly for static analysis of Go programs, some of which are listed below. Use the “Go reference” link above for more information about any package.

It also contains the golang.org/x/tools/gopls module, whose root package is a language-server protocol (LSP) server for Go. An LSP server analyses the source code of a project and responds to requests from a wide range of editors such as VSCode and Vim, allowing them to support IDE-like functionality.

Selected commands:

  • cmd/goimports formats a Go program like go fmt and additionally inserts import statements for any packages required by the file after it is edited.
  • cmd/callgraph prints the call graph of a Go program.
  • cmd/digraph is a utility for manipulating directed graphs in textual notation.
  • cmd/stringer generates declarations (including a String method) for “enum” types.
  • cmd/toolstash is a utility to simplify working with multiple versions of the Go toolchain.

These commands may be fetched with a command such as go install golang.org/x/tools/cmd/goimports@latest.

Selected packages:

  • go/ssa provides a static single-assignment form (SSA) intermediate representation (IR) for Go programs, similar to a typical compiler, for use by analysis tools.

  • go/packages provides a simple interface for loading, parsing, and type checking a complete Go program from source code.

  • go/analysis provides a framework for modular static analysis of Go programs.

  • go/callgraph provides call graphs of Go programs using a variety of algorithms with different trade-offs.

  • go/ast/inspector provides an optimized means of traversing a Go parse tree for use in analysis tools.

  • go/cfg provides a simple control-flow graph (CFG) for a Go function.

  • go/expect reads Go source files used as test inputs and interprets special comments within them as queries or assertions for testing.

  • go/gcexportdata and go/gccgoexportdata read and write the binary files containing type information used by the standard and gccgo compilers.

  • go/types/objectpath provides a stable naming scheme for named entities (“objects”) in the go/types API.

Numerous other packages provide more esoteric functionality.

Contributing

This repository uses Gerrit for code changes. To learn how to submit changes, see https://golang.org/doc/contribute.html.

The main issue tracker for the tools repository is located at https://github.com/golang/go/issues. Prefix your issue with “x/tools/(your subdir):” in the subject line, so it is easy to find.

JavaScript and CSS Formatting

This repository uses prettier to format JS and CSS files.

The version of prettier used is 1.18.2.

It is encouraged that all JS and CSS code be run through this before submitting a change. However, it is not a strict requirement enforced by CI.