Don't starve unverified bytes limit on unrequestable pieces

Solves issue described at #916 (comment).

Author: anacrolix

request-strategy-impls.go

@@ -88,12 +88,12 @@ type requestStrategyPiece struct {
 	p *Piece
 }
 
-func (r requestStrategyPiece) Request() bool {
-	return !r.p.ignoreForRequests() && r.p.purePriority() != PiecePriorityNone
+func (r requestStrategyPiece) CountUnverified() bool {
+	return r.p.hashing || r.p.marking || r.p.queuedForHash()
 }
 
-func (r requestStrategyPiece) NumPendingChunks() int {
-	return int(r.p.t.pieceNumPendingChunks(r.p.index))
+func (r requestStrategyPiece) Request() bool {
+	return !r.p.ignoreForRequests() && r.p.purePriority() != PiecePriorityNone
 }
 
-var _ request_strategy.Piece = (*requestStrategyPiece)(nil)
+var _ request_strategy.Piece = requestStrategyPiece{}

request-strategy/NOTES.md

@@ -0,0 +1,27 @@
+Rough notes on how requests are determined.
+
+piece ordering cache:
+
+- pieces are grouped by shared storage capacity and ordered by priority, availability, index and then infohash.
+- if a torrent does not have a storage cap, pieces are also filtered by whether requests should currently be made for them. this is because for torrents without a storage cap, there's no need to consider pieces that won't be requested.
+
+building a list of candidate requests for a peer:
+
+- pieces are scanned in order of the pre-sorted order for the storage group.
+- scanning stops when the cumulative piece length so far exceeds the storage capacity.
+- pieces are filtered by whether requests should currently be made for them (hashing, marking, already complete, etc.)
+- if requests were added to the consideration list, or the piece was in a partial state, the piece length is added to a cumulative total of unverified bytes.
+- if the cumulative total of unverified bytes reaches the configured limit (default 64MiB), piece scanning is halted.
+
+applying request state:
+
+- send the appropriate interest message if our interest doesn't match what the peer is seeing
+- sort all candidate requests by:
+  - allowed fast if we're being choked,
+  - piece priority,
+  - whether the request is already outstanding to the peer,
+  - whether the request is not pending from any peer
+  - if the request is outstanding from a peer:
+    - how many outstanding requests the existing peer has
+    - most recently requested
+  - least available piece

request-strategy/order.go

@@ -42,7 +42,8 @@ func pieceOrderLess(i, j *pieceRequestOrderItem) multiless.Computation {
 // Calls f with requestable pieces in order.
 func GetRequestablePieces(
 	input Input, pro *PieceRequestOrder,
-	f func(ih metainfo.Hash, pieceIndex int, orderState PieceRequestOrderState),
+	// Returns true if the piece should be considered against the unverified bytes limit.
+	requestPiece func(ih metainfo.Hash, pieceIndex int, orderState PieceRequestOrderState) bool,
 ) {
 	// Storage capacity left for this run, keyed by the storage capacity pointer on the storage
 	// TorrentImpl. A nil value means no capacity limit.
@@ -59,23 +60,26 @@ func GetRequestablePieces(
 		var t = input.Torrent(ih)
 		var piece = t.Piece(item.key.Index)
 		pieceLength := t.PieceLength()
+		// Storage limits will always apply against requestable pieces, since we need to keep the
+		// highest priority pieces, even if they're complete or in an undesirable state.
 		if storageLeft != nil {
 			if *storageLeft < pieceLength {
 				return false
 			}
 			*storageLeft -= pieceLength
 		}
-		if !piece.Request() || piece.NumPendingChunks() == 0 {
-			// TODO: Clarify exactly what is verified. Stuff that's being hashed should be
-			// considered unverified and hold up further requests.
+		if piece.Request() {
+			if !requestPiece(ih, item.key.Index, item.state) {
+				// No blocks are being considered from this piece, so it won't result in unverified
+				// bytes.
+				return true
+			}
+		} else if !piece.CountUnverified() {
+			// The piece is pristine, and we're not considering it for requests.
 			return true
 		}
-		if maxUnverifiedBytes != 0 && allTorrentsUnverifiedBytes+pieceLength > maxUnverifiedBytes {
-			return false
-		}
 		allTorrentsUnverifiedBytes += pieceLength
-		f(ih, item.key.Index, item.state)
-		return true
+		return maxUnverifiedBytes == 0 || allTorrentsUnverifiedBytes < maxUnverifiedBytes
 	})
 	return
 }

request-strategy/piece.go

@@ -1,6 +1,10 @@
 package requestStrategy
 
 type Piece interface {
+	// Whether requests should be made for this piece. This would be false for cases like the piece
+	// is currently being hashed, or already complete.
 	Request() bool
-	NumPendingChunks() int
+	// Whether the piece should be counted towards the unverified bytes limit. The intention is to
+	// prevent pieces being starved from the opportunity to move to the completed state.
+	CountUnverified() bool
 }

requesting.go

@@ -191,12 +191,12 @@ func (p *Peer) getDesiredRequestState() (desired desiredRequestState) {
 	requestStrategy.GetRequestablePieces(
 		input,
 		t.getPieceRequestOrder(),
-		func(ih InfoHash, pieceIndex int, pieceExtra requestStrategy.PieceRequestOrderState) {
+		func(ih InfoHash, pieceIndex int, pieceExtra requestStrategy.PieceRequestOrderState) bool {
 			if ih != *t.canonicalShortInfohash() {
-				return
+				return false
 			}
 			if !p.peerHasPiece(pieceIndex) {
-				return
+				return false
 			}
 			requestHeap.pieceStates[pieceIndex].Set(pieceExtra)
 			allowedFast := p.peerAllowedFast.Contains(pieceIndex)
@@ -222,6 +222,7 @@ func (p *Peer) getDesiredRequestState() (desired desiredRequestState) {
 				}
 				requestHeap.requestIndexes = append(requestHeap.requestIndexes, r)
 			})
+			return true
 		},
 	)
 	t.assertPendingRequests()

tests/README

@@ -0,0 +1 @@
+This directory contains integration style tests that probably run too long for regular unit testing. It's a separate module to avoid getting run by ./... in the root.

tests/go.mod

@@ -0,0 +1,3 @@
+module github.com/anacrolix/torrent/tests
+
+go 1.22.0

tests/go.work

@@ -0,0 +1,6 @@
+go 1.22.0
+
+use (
+	.
+	..
+)