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cmd/go/internal/modindex: avoid walking modules when not needed

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Due to a missed condition in CL 412394, we were walking all modules
(instead of just the ones contained in GOROOT) at each invocation of a
devel version of cmd/go.

Moreover, while we were running cmd/go tests, we were re-walking
GOROOT at each 'go' invocation in the test even though we expect
GOROOT to be stable within a test run.

This change always avoids walking non-GOROOT modules, and also adds a
salt (configurable via GODEBUG) and uses it to avoid walking GOROOT
modules when GOROOT is known to be stable (such as over the course of
a 'cmd/go' test run).

This should fix the cmd/go test timeouts that are currently occurring
on the dragonfly-amd64 builder, such as this one:
https://build.golang.org/log/21c01c3ae5490d387d84abeaf872b3a0a76ab8e5

Updates #53290.

Change-Id: Ic807d215831a3cd21c63e0bccd3d7acd10d8f2b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/412779
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
This commit is contained in:
Bryan C. Mills 2022-06-16 18:02:11 -04:00 committed by Gopher Robot
parent c2d373d5d1
commit 530511bacc
2 changed files with 36 additions and 22 deletions
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14
src/cmd/go/go_test.go
View file

@ -18,6 +18,7 @@ import (
"io"
"io/fs"
"log"
"math/rand"
"os"
"os/exec"
"path/filepath"
@ -128,6 +129,19 @@ func TestMain(m *testing.M) {
}
os.Setenv("CMDGO_TEST_RUN_MAIN", "true")
if strings.HasPrefix(runtime.Version(), "devel ") && godebug.Get("goindexsalt") == "" {
// We're going to execute a lot of cmd/go tests, so set a consistent salt
// via GODEBUG so that the modindex package can avoid walking an entire
// GOROOT module whenever it tries to use an index for that module.
indexSalt := rand.Int63()
v := os.Getenv("GODEBUG")
if v == "" {
os.Setenv("GODEBUG", fmt.Sprintf("goindexsalt=%d", indexSalt))
} else {
os.Setenv("GODEBUG", fmt.Sprintf("%s,goindexsalt=%d", v, indexSalt))
}
}
// $GO_GCFLAGS a compiler debug flag known to cmd/dist, make.bash, etc.
// It is not a standard go command flag; use os.Getenv, not cfg.Getenv.
if os.Getenv("GO_GCFLAGS") != "" {

44
src/cmd/go/internal/modindex/read.go
View file

@ -12,11 +12,11 @@ import (
"go/build"
"go/build/constraint"
"go/token"
"internal/godebug"
"internal/goroot"
"internal/unsafeheader"
"io/fs"
"math"
"os"
"path"
"path/filepath"
"runtime"
@ -39,15 +39,7 @@ import (
// It will be removed before the release.
// TODO(matloob): Remove enabled once we have more confidence on the
// module index.
var enabled = func() bool {
debug := strings.Split(os.Getenv("GODEBUG"), ",")
for _, f := range debug {
if f == "goindex=0" {
return false
}
}
return true
}()
var enabled bool = godebug.Get("goindex") != "0"
// ModuleIndex represents and encoded module index file. It is used to
// do the equivalent of build.Import of packages in the module and answer other
@ -61,26 +53,34 @@ type ModuleIndex struct {
var fcache par.Cache
var salt = godebug.Get("goindexsalt")
func moduleHash(modroot string, ismodcache bool) (cache.ActionID, error) {
// We expect modules stored within the module cache to be checksummed and
// immutable, and we expect released Go modules to change only infrequently
// (when the Go version changes).
if !ismodcache || !str.HasFilePathPrefix(modroot, cfg.GOROOT) {
// immutable, and we expect released modules within GOROOT to change only
// infrequently (when the Go version changes).
if !ismodcache && !str.HasFilePathPrefix(modroot, cfg.GOROOT) {
// The contents of this module may change over time. We don't want to pay
// the cost to detect changes and re-index whenever they occur, so just
// don't index it at all.
return cache.ActionID{}, ErrNotIndexed
}
h := cache.NewHash("moduleIndex")
fmt.Fprintf(h, "module index %s %s %v\n", runtime.Version(), indexVersion, modroot)
fmt.Fprintf(h, "module index %s %s %s %v\n", runtime.Version(), salt, indexVersion, modroot)
if strings.HasPrefix(runtime.Version(), "devel ") {
if str.HasFilePathPrefix(modroot, cfg.GOROOT) && strings.HasPrefix(runtime.Version(), "devel ") && salt == "" {
// This copy of the standard library is a development version, not a
// release. It could be based on a Git commit (like "devel go1.19-2a78e8afc0
// Wed Jun 15 00:06:24 2022 +0000") with or without changes on top of that
// commit, or it could be completly artificial due to lacking a `git` binary
// (like "devel gomote.XXXXX", as synthesized by "gomote push" as of
// 2022-06-15). Compute an inexpensive hash of its files using mtimes so
// that during development we can continue to exercise the logic for cached
// GOROOT indexes.
// release. It could be based on a Git commit (like
// "devel go1.19-2a78e8afc0 Wed Jun 15 00:06:24 2022 +0000") with or
// without changes on top of that commit, or it could be completly
// artificial due to lacking a `git` binary (like "devel gomote.XXXXX", as
// synthesized by "gomote push" as of 2022-06-15).
//
// If the user provided a unique salt via GODEBUG, we can trust that it is
// unique and just go with it. Otherwise, we compute an inexpensive hash of
// its files using mtimes so that during development we can continue to
// exercise the logic for cached GOROOT indexes.
//
// mtimes may be granular, imprecise, and loosely updated (see
// https://apenwarr.ca/log/20181113), but we don't expect Go contributors to