cmd/go: cache results of exec.LookPath

This CL package exec.LookPath to internal/cfg.LookPath and adds cache.

BenchmarkLookPath-4     24149096                50.48 ns/op            0 B/op          0 allocs/op

Fixes golang#36768

Change-Id: I199a780d1eab9bd5397bb3759bb42191fff716e9

Change-Id: I199a780d1eab9bd5397bb3759bb42191fff716e9
GitHub-Last-Rev: 04cb24b
GitHub-Pull-Request: golang#61464

src/cmd/go/internal/cfg/bench_test.go

@@ -0,0 +1,21 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cfg
+
+import (
+	"internal/testenv"
+	"testing"
+)
+
+func BenchmarkLookPath(b *testing.B) {
+	testenv.MustHaveExecPath(b, "go")
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, err := LookPath("go")
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}

src/cmd/go/internal/cfg/cfg.go

@@ -15,7 +15,6 @@ import (
 	"internal/cfg"
 	"io"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -161,7 +160,7 @@ func defaultContext() build.Context {
 		if ctxt.CgoEnabled {
 			if os.Getenv("CC") == "" {
 				cc := DefaultCC(ctxt.GOOS, ctxt.GOARCH)
-				if _, err := exec.LookPath(cc); err != nil {
+				if _, err := LookPath(cc); err != nil {
 					ctxt.CgoEnabled = false
 				}
 			}

src/cmd/go/internal/cfg/lookpath.go

@@ -0,0 +1,21 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cfg
+
+import (
+	"cmd/go/internal/par"
+	"os/exec"
+)
+
+var lookPathCache par.ErrCache[string, string]
+
+// LookPath wraps exec.LookPath and caches the result
+// which can be called by multiple Goroutines at the same time.
+func LookPath(file string) (path string, err error) {
+	return lookPathCache.Do(file,
+		func() (string, error) {
+			return exec.LookPath(file)
+		})
+}

src/cmd/go/internal/generate/generate.go

@@ -479,7 +479,7 @@ func (g *Generator) exec(words []string) {
 		// intends to use the same 'go' as 'go generate' itself.
 		// Prefer to resolve the binary from GOROOT/bin, and for consistency
 		// prefer to resolve any other commands there too.
-		gorootBinPath, err := exec.LookPath(filepath.Join(cfg.GOROOTbin, path))
+		gorootBinPath, err := cfg.LookPath(filepath.Join(cfg.GOROOTbin, path))
 		if err == nil {
 			path = gorootBinPath
 		}

src/cmd/go/internal/load/pkg.go

@@ -18,7 +18,6 @@ import (
 	"internal/platform"
 	"io/fs"
 	"os"
-	"os/exec"
 	pathpkg "path"
 	"path/filepath"
 	"runtime"
@@ -2483,7 +2482,7 @@ func (p *Package) setBuildInfo(ctx context.Context, autoVCS bool) {
 			goto omitVCS
 		}
 		if cfg.BuildBuildvcs == "auto" && vcsCmd != nil && vcsCmd.Cmd != "" {
-			if _, err := exec.LookPath(vcsCmd.Cmd); err != nil {
+			if _, err := cfg.LookPath(vcsCmd.Cmd); err != nil {
 				// We fould a repository, but the required VCS tool is not present.
 				// "-buildvcs=auto" means that we should silently drop the VCS metadata.
 				goto omitVCS

src/cmd/go/internal/script/cmds.go

@@ -5,6 +5,7 @@
 package script
 
 import (
+	"cmd/go/internal/cfg"
 	"cmd/go/internal/robustio"
 	"errors"
 	"fmt"
@@ -824,7 +825,7 @@ func Program(name string, cancel func(*exec.Cmd) error, waitDelay time.Duration)
 		},
 		func(s *State, args ...string) (WaitFunc, error) {
 			lookPathOnce.Do(func() {
-				path, pathErr = exec.LookPath(name)
+				path, pathErr = cfg.LookPath(name)
 			})
 			if pathErr != nil {
 				return nil, pathErr

src/cmd/go/internal/script/scripttest/scripttest.go

@@ -7,10 +7,10 @@ package scripttest
 
 import (
 	"bufio"
+	"cmd/go/internal/cfg"
 	"cmd/go/internal/script"
 	"errors"
 	"io"
-	"os/exec"
 	"strings"
 	"testing"
 )
@@ -137,7 +137,7 @@ func CachedExec() script.Cond {
 	return script.CachedCondition(
 		"<suffix> names an executable in the test binary's PATH",
 		func(name string) (bool, error) {
-			_, err := exec.LookPath(name)
+			_, err := cfg.LookPath(name)
 			return err == nil, nil
 		})
 }

src/cmd/go/internal/toolchain/select.go

@@ -13,7 +13,6 @@ import (
 	"io/fs"
 	"log"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strconv"
@@ -283,7 +282,7 @@ func Exec(gotoolchain string) {
 	// Look in PATH for the toolchain before we download one.
 	// This allows custom toolchains as well as reuse of toolchains
 	// already installed using go install golang.org/dl/go1.2.3@latest.
-	if exe, err := exec.LookPath(gotoolchain); err == nil {
+	if exe, err := cfg.LookPath(gotoolchain); err == nil {
 		execGoToolchain(gotoolchain, "", exe)
 	}
 

src/cmd/go/internal/vcs/vcs.go

@@ -680,7 +680,7 @@ func (v *Cmd) run1(dir string, cmdline string, keyval []string, verbose bool) ([
 		args = args[2:]
 	}
 
-	_, err := exec.LookPath(v.Cmd)
+	_, err := cfg.LookPath(v.Cmd)
 	if err != nil {
 		fmt.Fprintf(os.Stderr,
 			"go: missing %s command. See https://golang.org/s/gogetcmd\n",

src/cmd/go/internal/work/build.go

@@ -11,7 +11,6 @@ import (
 	"fmt"
 	"go/build"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strconv"
@@ -899,7 +898,7 @@ func FindExecCmd() []string {
 	if cfg.Goos == runtime.GOOS && cfg.Goarch == runtime.GOARCH {
 		return ExecCmd
 	}
-	path, err := exec.LookPath(fmt.Sprintf("go_%s_%s_exec", cfg.Goos, cfg.Goarch))
+	path, err := cfg.LookPath(fmt.Sprintf("go_%s_%s_exec", cfg.Goos, cfg.Goarch))
 	if err == nil {
 		ExecCmd = []string{path}
 	}

src/cmd/go/internal/work/buildid.go

@@ -270,7 +270,7 @@ func (b *Builder) gccToolID(name, language string) (id, exe string, err error) {
 		}
 		exe = fields[0]
 		if !strings.ContainsAny(exe, `/\`) {
-			if lp, err := exec.LookPath(exe); err == nil {
+			if lp, err := cfg.LookPath(exe); err == nil {
 				exe = lp
 			}
 		}

src/cmd/go/internal/work/exec.go

@@ -2373,7 +2373,11 @@ func (b *Builder) runOut(a *Action, dir string, env []string, cmdargs ...any) ([
 	}
 
 	var buf bytes.Buffer
-	cmd := exec.Command(cmdline[0], cmdline[1:]...)
+	path, err := cfg.LookPath(cmdline[0])
+	if err != nil {
+		return nil, err
+	}
+	cmd := exec.Command(path, cmdline[1:]...)
 	if cmd.Path != "" {
 		cmd.Args[0] = cmd.Path
 	}
@@ -2397,7 +2401,7 @@ func (b *Builder) runOut(a *Action, dir string, env []string, cmdargs ...any) ([
 
 	cmd.Env = append(cmd.Env, env...)
 	start := time.Now()
-	err := cmd.Run()
+	err = cmd.Run()
 	if a != nil && a.json != nil {
 		aj := a.json
 		aj.Cmd = append(aj.Cmd, joinUnambiguously(cmdline))
@@ -3017,7 +3021,7 @@ func (b *Builder) gccCompilerID(compiler string) (id cache.ActionID, ok bool) {
 	//
 	// Otherwise, we compute a new validation description
 	// and compiler id (below).
-	exe, err := exec.LookPath(compiler)
+	exe, err := cfg.LookPath(compiler)
 	if err != nil {
 		return cache.ActionID{}, false
 	}

src/cmd/go/internal/work/gccgo.go

@@ -32,7 +32,7 @@ func init() {
 	if GccgoName == "" {
 		GccgoName = "gccgo"
 	}
-	GccgoBin, gccgoErr = exec.LookPath(GccgoName)
+	GccgoBin, gccgoErr = cfg.LookPath(GccgoName)
 }
 
 func (gccgoToolchain) compiler() string {