x/telemetry: do not always fork cmd/go child

[rsc]

x/telemetry is forking a new go child process every time the go command is run, and then the child looks around and decides not to upload anything. It should look around before forking and avoid the fork 99% of the time.

[findleyr]

Also: per discussion we should rename the X_TELEMETRY_CHILD environment variable
to something clearly go specific, such as GO_TELEMETRY_CHILD.

[sparrowhe]

I tried making some change of this issue:

diff --git a/start.go b/start.go
index 426a18b..b7baef8 100644
--- a/start.go
+++ b/start.go
@@ -242,6 +242,31 @@ func child(reportCrashes, upload bool, uploadStartTime time.Time, uploadURL stri
 		})
 	}
 	if upload {
+
+		// golang/go#67700: do not always fork cmd/go child
+		// Pre-check if there are any coditions that would prevent uploading anything.
+
+		if mode, _ := telemetry.Default.Mode(); mode == "off" {
+			// There's no work to be done if telemetry is turned off.
+			return
+		}
+		if telemetry.Default.LocalDir() == "" {
+			// The telemetry dir wasn't initialized properly, probably because
+			// os.UserConfigDir did not complete successfully. In that case
+			// there are no counters to upload, so we should just do nothing.
+			return
+		}
+		tokenfilepath := filepath.Join(telemetry.Default.LocalDir(), "upload.token")
+		ok, err := acquireUploadToken(tokenfilepath)
+		if err != nil {
+			log.Printf("error acquiring upload token: %v", err)
+			return
+		} else if !ok {
+			// It hasn't been a day since the last upload.Run attempt or there's
+			// a concurrently running uploader.
+			return
+		}
+
 		g.Go(func() error {
 			uploaderChild(uploadStartTime, uploadURL)
 			return nil
@@ -251,26 +276,6 @@ func child(reportCrashes, upload bool, uploadStartTime time.Time, uploadURL stri
 }
 
 func uploaderChild(asof time.Time, uploadURL string) {
-	if mode, _ := telemetry.Default.Mode(); mode == "off" {
-		// There's no work to be done if telemetry is turned off.
-		return
-	}
-	if telemetry.Default.LocalDir() == "" {
-		// The telemetry dir wasn't initialized properly, probably because
-		// os.UserConfigDir did not complete successfully. In that case
-		// there are no counters to upload, so we should just do nothing.
-		return
-	}
-	tokenfilepath := filepath.Join(telemetry.Default.LocalDir(), "upload.token")
-	ok, err := acquireUploadToken(tokenfilepath)
-	if err != nil {
-		log.Printf("error acquiring upload token: %v", err)
-		return
-	} else if !ok {
-		// It hasn't been a day since the last upload.Run attempt or there's
-		// a concurrently running uploader.
-		return
-	}
 	if err := upload.Run(upload.RunConfig{
 		UploadURL: uploadURL,
 		LogWriter: os.Stderr,

This is my first time contributing code, please let me know if I did something wrong. :)

[gopherbot]

Change https://go.dev/cl/589375 mentions this issue: telemetry: acquire upload token before starting uploader child

[matloob]

Hi @sparrowhe I already had a change to fix this (I just incorrectly annotated the issue number on the commit description).