cmd/go: parallelize fmt

Currently go fmt formats all files sequentially.
That's a shame. Parallelize it over files.

Reduces time of go fmt ./... in std lib
from ~6.1s to ~0.9s.

Reduces time of go fmt github.com/google/syzkaller/...
from ~5.2s to ~1.8s.

Change-Id: I3d27fc25326106b2a4781e13506a25c12d5bcdc5
Reviewed-on: https://go-review.googlesource.com/45491
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/cmd/go/internal/fmtcmd/fmt.go b/src/cmd/go/internal/fmtcmd/fmt.go
index 0563a0410b377faeade56963b1afa3a8bd88ae2b..5839028b07da57fa4d2b97edd75cc8bdc2219260 100644 (file)
--- a/src/cmd/go/internal/fmtcmd/fmt.go
+++ b/src/cmd/go/internal/fmtcmd/fmt.go
@@ -8,6 +8,8 @@ package fmtcmd
 import (
        "os"
        "path/filepath"
+       "runtime"
+       "sync"
 
        "cmd/go/internal/base"
        "cmd/go/internal/cfg"
@@ -41,13 +43,29 @@ See also: go fix, go vet.
 
 func runFmt(cmd *base.Command, args []string) {
        gofmt := gofmtPath()
+       procs := runtime.GOMAXPROCS(0)
+       var wg sync.WaitGroup
+       wg.Add(procs)
+       fileC := make(chan string, 2*procs)
+       for i := 0; i < procs; i++ {
+               go func() {
+                       defer wg.Done()
+                       for file := range fileC {
+                               base.Run(str.StringList(gofmt, "-l", "-w", file))
+                       }
+               }()
+       }
        for _, pkg := range load.Packages(args) {
                // Use pkg.gofiles instead of pkg.Dir so that
                // the command only applies to this package,
                // not to packages in subdirectories.
                files := base.FilterDotUnderscoreFiles(base.RelPaths(pkg.Internal.AllGoFiles))
-               base.Run(str.StringList(gofmt, "-l", "-w", files))
+               for _, file := range files {
+                       fileC <- file
+               }
        }
+       close(fileC)
+       wg.Wait()
 }
 
 func gofmtPath() string {