From ad566d672c86c1682c175db7164c0b72717c27ea Mon Sep 17 00:00:00 2001
From: John Smith <>
Date: Fri, 2 Jun 2017 16:22:31 +0200
Subject: [PATCH] Comments

---
 .../metainfoFetcher/metainfo_fetcher.go       | 33 ++++++++++++-------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/service/torrent/metainfoFetcher/metainfo_fetcher.go b/service/torrent/metainfoFetcher/metainfo_fetcher.go
index e16feab0..ba13c435 100644
--- a/service/torrent/metainfoFetcher/metainfo_fetcher.go
+++ b/service/torrent/metainfoFetcher/metainfo_fetcher.go
@@ -1,7 +1,6 @@
 package metainfoFetcher
 
 import (
-	"math"
 	"sync"
 	"time"
 
@@ -199,18 +198,28 @@ func (fetcher *MetainfoFetcher) gotResult(r Result) {
 }
 
 func (fetcher *MetainfoFetcher) removeOldFailures() {
-	// Cooldown is disabled
 	if fetcher.baseFailCooldown < 0 {
+		// XXX: Cooldown is disabled.
+		// this means that if any attempt to fetch metadata fails
+		// it will never be retried. it also means that
+		// fetcher.failedOperations will keep accumulating torrent IDs
+		// that are never freed.
 		return
 	}
 
-	maxCd := time.Duration(fetcher.maxFailCooldown) * time.Second
+	max := time.Duration(fetcher.maxFailCooldown) * time.Second
 	now := time.Now()
 	for id, failTime := range fetcher.failedOperations {
-		cdMult := int(math.Pow(2, float64(fetcher.numFails[id]-1)))
-		cd := time.Duration(cdMult*fetcher.baseFailCooldown) * time.Second
-		if cd > maxCd {
-			cd = maxCd
+		// double the amount of time waited for ever failed attempt.
+		// | nfailed | cooldown
+		// | 1       | 2 * base
+		// | 2       | 4 * base
+		// | 3       | 8 * base
+		// integers inside fetcher.numFails are never less than or equal to zero
+		mul := 1 << uint(fetcher.numFails[id]-1)
+		cd := time.Duration(mul * fetcher.baseFailCooldown) * time.Second
+		if cd > max {
+			cd = max
 		}
 
 		if failTime.Add(cd).Before(now) {
@@ -222,9 +231,8 @@ func (fetcher *MetainfoFetcher) removeOldFailures() {
 }
 
 func (fetcher *MetainfoFetcher) fillQueue() {
-	toFill := fetcher.queueSize - len(fetcher.queue)
-
-	if toFill <= 0 {
+	if left := fetcher.queueSize - len(fetcher.queue); left <= 0 {
+		// queue is already full.
 		return
 	}
 
@@ -273,13 +281,15 @@ func (fetcher *MetainfoFetcher) fillQueue() {
 
 	for _, T := range dbTorrents {
 		for _, v := range fetcher.queue {
+			// skip torrents that are already being processed.
 			if v.torrent.ID == T.ID {
 				continue
 			}
 		}
 		if _, ok := fetcher.failedOperations[T.ID]; ok {
 			// do not start new jobs that have recently failed.
-			// removeOldFailures() takes care of that.
+			// these are on cooldown and will be removed from
+			// fetcher.failedOperations when time is up.
 			continue
 		}
 
@@ -303,6 +313,7 @@ func (fetcher *MetainfoFetcher) run() {
 	for {
 		fetcher.removeOldFailures()
 		fetcher.fillQueue()
+
 		select {
 		case <-fetcher.done:
 			log.Infof("Got done signal on main loop, leaving...")