From: Tom Clegg <tom@curoverse.com>
Date: Thu, 4 Aug 2016 21:44:34 +0000 (-0400)
Subject: Simplify write flusher using a time.Ticker.
X-Git-Tag: 1.1.0~803
X-Git-Url: https://git.arvados.org/arvados.git/commitdiff_plain/13c821b6dd20ed658db9c6c3db0b8d10d9175fbb

Simplify write flusher using a time.Ticker.

No issue #
---

diff --git a/services/crunch-run/logging.go b/services/crunch-run/logging.go
index a2aa5c6b48..4f8f95c9a6 100644
--- a/services/crunch-run/logging.go
+++ b/services/crunch-run/logging.go
@@ -18,7 +18,7 @@ type Timestamper func(t time.Time) string
 // Logging plumbing:
 //
 // ThrottledLogger.Logger -> ThrottledLogger.Write ->
-// ThrottledLogger.buf -> ThrottledLogger.flusher -> goWriter ->
+// ThrottledLogger.buf -> ThrottledLogger.flusher ->
 // ArvLogWriter.Write -> CollectionFileWriter.Write | Api.Create
 //
 // For stdout/stderr ReadWriteLines additionally runs as a goroutine to pull
@@ -51,10 +51,11 @@ func RFC3339Timestamp(t time.Time) string {
 // tl.Immediate, if tl.Immediate is not nil.
 func (tl *ThrottledLogger) Write(p []byte) (n int, err error) {
 	tl.Mutex.Lock()
+	defer tl.Mutex.Unlock()
+
 	if tl.buf == nil {
 		tl.buf = &bytes.Buffer{}
 	}
-	defer tl.Mutex.Unlock()
 
 	now := tl.Timestamper(time.Now().UTC())
 	sc := bufio.NewScanner(bytes.NewBuffer(p))
@@ -77,39 +78,28 @@ func (tl *ThrottledLogger) Write(p []byte) (n int, err error) {
 // Periodically check the current buffer; if not empty, send it on the
 // channel to the goWriter goroutine.
 func (tl *ThrottledLogger) flusher() {
-	bufchan := make(chan *bytes.Buffer)
-	bufterm := make(chan bool)
-
-	// Use a separate goroutine for the actual write so that the writes are
-	// actually initiated closer every 1s instead of every
-	// 1s + (time to it takes to write).
-	go goWriter(tl.writer, bufchan, bufterm)
-
-	// We use a separate "stopping" var here to ensure we flush
-	// tl.buf after tl.stop becomes true.
-	stopping := false
-	for !stopping {
-		time.Sleep(time.Second)
-		stopping = tl.stop
+	ticker := time.NewTicker(time.Second)
+	defer ticker.Stop()
+	for range ticker.C {
+		// We use a separate "stopping" var here to ensure we flush
+		// tl.buf after tl.stop becomes true.
+		stopping := tl.stop
+
+		var ready *bytes.Buffer
+
 		tl.Mutex.Lock()
-		if tl.buf != nil && tl.buf.Len() > 0 {
-			oldbuf := tl.buf
-			tl.buf = nil
-			bufchan <- oldbuf
-		}
+		ready, tl.buf = tl.buf, nil
 		tl.Mutex.Unlock()
-	}
-	close(bufchan)
-	<-bufterm
-	tl.flusherDone <- true
-}
 
-// Receive buffers from a channel and send to the underlying Writer
-func goWriter(writer io.Writer, c <-chan *bytes.Buffer, t chan<- bool) {
-	for b := range c {
-		writer.Write(b.Bytes())
+		if ready != nil && ready.Len() > 0 {
+			tl.writer.Write(ready.Bytes())
+		}
+
+		if stopping {
+			break
+		}
 	}
-	t <- true
+	close(tl.flusherDone)
 }
 
 // Close the flusher goroutine and wait for it to complete, then close the