Use Mutex when modifying failedOperations, add exponential cooldown

Just to be safe, won't allow concurrent goroutines to modify the map.

The exponential cooldown prevents newer torrents with no seeds
blocking older ones with seeds, when there are enough failures that a
cooldown event would fill the queue with only failed torrents.

config/metainfoFetcher.go

@@ -1,22 +1,24 @@
 package config
 
 type MetainfoFetcherConfig struct {
-	QueueSize      int `json:"queue_size"`
-	Timeout        int `json:"timeout"`
-	MaxDays        int `json:"max_days"`
-	FailCooldown   int `json:"fail_cooldown"`
-	WakeUpInterval int `json:"wake_up_interval"`
+	QueueSize        int `json:"queue_size"`
+	Timeout          int `json:"timeout"`
+	MaxDays          int `json:"max_days"`
+	BaseFailCooldown int `json:"base_fail_cooldown"`
+	MaxFailCooldown  int `json:"max_fail_cooldown"`
+	WakeUpInterval   int `json:"wake_up_interval"`
 
 	UploadRateLimiter   int `json:"upload_rate_limiter"`
 	DownloadRateLimiter int `json:"download_rate_limiter"`
 }
 
 var DefaultMetainfoFetcherConfig = MetainfoFetcherConfig{
-	QueueSize:      10,
-	Timeout:        120, // 2 min
-	MaxDays:        90,
-	FailCooldown:   30 * 60, // in seconds, when failed torrents will be able to be fetched again.
-	WakeUpInterval: 300, // 5 min
+	QueueSize:        10,
+	Timeout:          120, // 2 min
+	MaxDays:          90,
+	BaseFailCooldown: 30 * 60, // in seconds, when failed torrents will be able to be fetched again.
+	MaxFailCooldown:  48 * 60 * 60,
+	WakeUpInterval:   300, // 5 min
 
 	UploadRateLimiter:   1024, // kbps
 	DownloadRateLimiter: 1024,

service/torrent/metainfoFetcher/metainfoFetcher.go

@@ -10,6 +10,7 @@ import (
 	serviceBase "github.com/ewhal/nyaa/service"
 	torrentService "github.com/ewhal/nyaa/service/torrent"
 	"golang.org/x/time/rate"
+	"math"
 	"sync"
 	"time"
 )
@@ -20,11 +21,14 @@ type MetainfoFetcher struct {
 	queueSize        int
 	timeout          int
 	maxDays          int
-	failCooldown     int
+	baseFailCooldown int
+	maxFailCooldown  int
 	done             chan int
 	queue            []*FetchOperation
 	queueMutex       sync.Mutex
 	failedOperations map[uint]time.Time
+	numFails         map[uint]int
+	failsMutex       sync.Mutex
 	wakeUp           *time.Ticker
 	wg               sync.WaitGroup
 }
@@ -48,9 +52,11 @@ func New(fetcherConfig *config.MetainfoFetcherConfig) (fetcher *MetainfoFetcher,
 		queueSize:        fetcherConfig.QueueSize,
 		timeout:          fetcherConfig.Timeout,
 		maxDays:          fetcherConfig.MaxDays,
-		failCooldown:     fetcherConfig.FailCooldown,
+		baseFailCooldown: fetcherConfig.BaseFailCooldown,
+		maxFailCooldown:  fetcherConfig.MaxFailCooldown,
 		done:             make(chan int, 1),
 		failedOperations: make(map[uint]time.Time),
+		numFails:         make(map[uint]int),
 		wakeUp:           time.NewTicker(time.Second * time.Duration(fetcherConfig.WakeUpInterval)),
 	}
 
@@ -95,6 +101,26 @@ func (fetcher *MetainfoFetcher) removeFromQueue(op *FetchOperation) bool {
 	return false
 }
 
+func (fetcher *MetainfoFetcher) markAsFailed(tID uint) {
+	fetcher.failsMutex.Lock()
+	defer fetcher.failsMutex.Unlock()
+
+	if n, ok := fetcher.numFails[tID]; ok {
+		fetcher.numFails[tID] = n + 1
+	} else {
+		fetcher.numFails[tID] = 1
+	}
+
+	fetcher.failedOperations[tID] = time.Now()
+}
+
+func (fetcher *MetainfoFetcher) removeFromFailed(tID uint) {
+	fetcher.failsMutex.Lock()
+	defer fetcher.failsMutex.Unlock()
+
+	delete(fetcher.failedOperations, tID)
+}
+
 func updateFileList(dbEntry model.Torrent, info *metainfo.Info) error {
 	torrentFiles := info.UpvertedFiles()
 	log.Infof("TID %d has %d files.", dbEntry.ID, len(torrentFiles))
@@ -152,7 +178,7 @@ func (fetcher *MetainfoFetcher) gotResult(r Result) {
 	}
 
 	if !updatedSuccessfully {
-		fetcher.failedOperations[r.operation.torrent.ID] = time.Now()
+		fetcher.markAsFailed(r.operation.torrent.ID)
 	}
 
 	fetcher.removeFromQueue(r.operation)
@@ -160,16 +186,23 @@ func (fetcher *MetainfoFetcher) gotResult(r Result) {
 
 func (fetcher *MetainfoFetcher) removeOldFailures() {
 	// Cooldown is disabled
-	if fetcher.failCooldown < 0 {
+	if fetcher.baseFailCooldown < 0 {
 		return
 	}
 
+	maxCd := time.Duration(fetcher.maxFailCooldown) * time.Second
 	now := time.Now()
 	for id, failTime := range fetcher.failedOperations {
-		if failTime.Add(time.Duration(fetcher.failCooldown) * time.Second).Before(now) {
-			log.Infof("Torrent TID %d gone through cooldown, removing from failures")
+		cdMult := int(math.Pow(2, float64(fetcher.numFails[id] - 1)))
+		cd := time.Duration(cdMult * fetcher.baseFailCooldown) * time.Second
+		if cd > maxCd {
+			cd = maxCd
+		}
+
+		if failTime.Add(cd).Before(now) {
+			log.Infof("Torrent TID %d gone through cooldown, removing from failures", id)
 			// Deleting keys inside a loop seems to be safe.
-			delete(fetcher.failedOperations, id)
+			fetcher.removeFromFailed(id)
 		}
 	}
 }