From c298ce2eb2de598afba47a7ce7cce3bdd9abc5ca Mon Sep 17 00:00:00 2001
From: h31p <alex.kushnaryov@gmail.com>
Date: Tue, 12 Nov 2019 21:40:16 +0200
Subject: [PATCH] dynamically adjust readahead, for nearly sequential download

---
 src/server/torr/Torrent.go                | 14 +++++++++++++-
 src/server/torr/storage/memcache/Cache.go |  7 +++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/server/torr/Torrent.go b/src/server/torr/Torrent.go
index 1d54208..a10de68 100644
--- a/src/server/torr/Torrent.go
+++ b/src/server/torr/Torrent.go
@@ -6,6 +6,7 @@ import (
 	"sort"
 	"sync"
 	"time"
+	"fmt"
 
 	"server/settings"
 	"server/utils"
@@ -184,6 +185,17 @@ func (t *Torrent) progressEvent() {
 	}
 	t.muTorrent.Unlock()
 	t.lastTimeSpeed = time.Now()
+	if (t.BytesReadUsefulData > settings.Get().PreloadBufferSize) {
+		adj := int64((int(t.cache.GetState().PiecesLength) * t.Torrent.Stats().ActivePeers) / (1 + t.cache.ReadersLen()))
+		switch {
+			case adj < t.cache.GetState().PiecesLength:
+				adj = t.cache.GetState().PiecesLength
+			case adj > t.cache.GetState().PiecesLength * 4:
+				adj = t.cache.GetState().PiecesLength * 4
+		}
+		t.cache.AdjustRA(adj)
+		log.Println("Status:", t.Name(), "S:", fmt.Sprintf("%8s", utils.Format(t.DownloadSpeed)), "P:", fmt.Sprintf("%2d", t.Torrent.Stats().ActivePeers), "/", fmt.Sprintf("%2d", t.Torrent.Stats().TotalPeers), "R:", t.cache.ReadersLen(), "RA:", utils.Format(float64(adj)))
+	}
 }
 
 func (t *Torrent) expired() bool {
@@ -223,7 +235,7 @@ func (t *Torrent) NewReader(file *torrent.File, readahead int64) *reader.Reader
 	defer t.muReader.Unlock()
 	reader := reader.NewReader(file)
 	if readahead <= 0 {
-		readahead = utils.GetReadahead()
+		readahead = t.cache.GetState().PiecesLength
 	}
 	reader.SetReadahead(readahead)
 	t.cache.AddReader(reader)
diff --git a/src/server/torr/storage/memcache/Cache.go b/src/server/torr/storage/memcache/Cache.go
index 36e084c..6569b04 100644
--- a/src/server/torr/storage/memcache/Cache.go
+++ b/src/server/torr/storage/memcache/Cache.go
@@ -211,3 +211,10 @@ func (c *Cache) ReadersLen() int {
 	}
 	return len(c.readers)
 }
+
+func (c *Cache) AdjustRA(readahead int64) {
+	for r, _ := range c.readers {
+		r.SetReadahead(readahead)
+	}
+}
+