Add --tail=NUM to limit the number of items to keep in memory

CHANGELOG.md

@@ -42,7 +42,14 @@ CHANGELOG
       ```vim
       let g:fzf_layout = { 'tmux': '100%,70%' }
       ```
-- (Windows) fzf now works on Git bash (mintty) out of the box via winpty integration
+- Better Windows Support
+    - fzf now works on Git bash (mintty) out of the box via winpty integration
+    - Many fixes and improvements for Windows
+- Added `--tail=NUM` option to limit the number of items to keep in memory. This is useful when you want to browse an endless stream of data (e.g. log stream) with fzf while limiting memory usage.
+  ```sh
+  # Interactive filtering of a log stream
+  tail -f *.log | fzf --tail 100000 --tac --no-sort --exact
+  ```
 - man page is now embedded in the binary; `fzf --man` to see it
 - Changed the default `--scroll-off` to 3, as we think it's a better default
 - Process started by `execute` action now directly writes to and reads from `/dev/tty`. Manual `/dev/tty` redirection for interactive programs is no longer required.

man/man1/fzf.1

@@ -99,6 +99,16 @@ interface rather than a "fuzzy finder". You can later enable the search using
 .B "+s, --no-sort"
 Do not sort the result
 .TP
+.B "--tail=NUM"
+Maximum number of items to keep in memory. This is useful when you want to
+browse an endless stream of data (e.g. log stream) with fzf while limiting
+memory usage.
+.RS
+e.g.
+     \fB# Interactive filtering of a log stream
+     tail -f *.log | fzf --tail 100000 --tac --no-sort --exact\fR
+.RE
+.TP
 .B "--track"
 Make fzf track the current selection when the result list is updated.
 This can be useful when browsing logs using fzf with sorting disabled. It is

src/chunklist.go

@@ -48,7 +48,12 @@ func CountItems(cs []*Chunk) int {
 	if len(cs) == 0 {
 		return 0
 	}
-	return chunkSize*(len(cs)-1) + cs[len(cs)-1].count
+	if len(cs) == 1 {
+		return cs[0].count
+	}
+
+	// First chunk might not be full due to --tail=N
+	return cs[0].count + chunkSize*(len(cs)-2) + cs[len(cs)-1].count
 }
 
 // Push adds the item to the list
@@ -72,18 +77,53 @@ func (cl *ChunkList) Clear() {
 }
 
 // Snapshot returns immutable snapshot of the ChunkList
-func (cl *ChunkList) Snapshot() ([]*Chunk, int) {
+func (cl *ChunkList) Snapshot(tail int) ([]*Chunk, int, bool) {
 	cl.mutex.Lock()
 
+	changed := false
+	if tail > 0 && CountItems(cl.chunks) > tail {
+		changed = true
+		// Find the number of chunks to keep
+		numChunks := 0
+		for left, i := tail, len(cl.chunks)-1; left > 0 && i >= 0; i-- {
+			numChunks++
+			left -= cl.chunks[i].count
+		}
+
+		// Copy the chunks to keep
+		ret := make([]*Chunk, numChunks)
+		copy(ret, cl.chunks[len(cl.chunks)-numChunks:])
+
+		for left, i := tail, len(ret)-1; i >= 0; i-- {
+			chunk := ret[i]
+			if chunk.count > left {
+				newChunk := *chunk
+				newChunk.count = left
+				oldCount := chunk.count
+				for i := 0; i < left; i++ {
+					newChunk.items[i] = chunk.items[oldCount-left+i]
+				}
+				ret[i] = &newChunk
+				break
+			}
+			left -= chunk.count
+		}
+		cl.chunks = ret
+	}
+
 	ret := make([]*Chunk, len(cl.chunks))
 	copy(ret, cl.chunks)
 
-	// Duplicate the last chunk
+	// Duplicate the first and the last chunk
 	if cnt := len(ret); cnt > 0 {
+		if tail > 0 && cnt > 1 {
+			newChunk := *ret[0]
+			ret[0] = &newChunk
+		}
 		newChunk := *ret[cnt-1]
 		ret[cnt-1] = &newChunk
 	}
 
 	cl.mutex.Unlock()
-	return ret, CountItems(ret)
+	return ret, CountItems(ret), changed
 }

src/chunklist_test.go

@@ -17,7 +17,7 @@ func TestChunkList(t *testing.T) {
 	})
 
 	// Snapshot
-	snapshot, count := cl.Snapshot()
+	snapshot, count, _ := cl.Snapshot(0)
 	if len(snapshot) > 0 || count > 0 {
 		t.Error("Snapshot should be empty now")
 	}
@@ -32,7 +32,7 @@ func TestChunkList(t *testing.T) {
 	}
 
 	// But the new snapshot should contain the added items
-	snapshot, count = cl.Snapshot()
+	snapshot, count, _ = cl.Snapshot(0)
 	if len(snapshot) != 1 && count != 2 {
 		t.Error("Snapshot should not be empty now")
 	}
@@ -61,7 +61,7 @@ func TestChunkList(t *testing.T) {
 	}
 
 	// New snapshot
-	snapshot, count = cl.Snapshot()
+	snapshot, count, _ = cl.Snapshot(0)
 	if len(snapshot) != 3 || !snapshot[0].IsFull() ||
 		!snapshot[1].IsFull() || snapshot[2].IsFull() || count != chunkSize*2+2 {
 		t.Error("Expected two full chunks and one more chunk")
@@ -78,3 +78,39 @@ func TestChunkList(t *testing.T) {
 		t.Error("Unexpected number of items:", lastChunkCount)
 	}
 }
+
+func TestChunkListTail(t *testing.T) {
+	cl := NewChunkList(func(item *Item, s []byte) bool {
+		item.text = util.ToChars(s)
+		return true
+	})
+	total := chunkSize*2 + chunkSize/2
+	for i := 0; i < total; i++ {
+		cl.Push([]byte(fmt.Sprintf("item %d", i)))
+	}
+
+	snapshot, count, changed := cl.Snapshot(0)
+	assertCount := func(expected int, shouldChange bool) {
+		if count != expected || CountItems(snapshot) != expected {
+			t.Errorf("Unexpected count: %d (expected: %d)", count, expected)
+		}
+		if changed != shouldChange {
+			t.Error("Unexpected change status")
+		}
+	}
+	assertCount(total, false)
+
+	tail := chunkSize + chunkSize/2
+	snapshot, count, changed = cl.Snapshot(tail)
+	assertCount(tail, true)
+
+	snapshot, count, changed = cl.Snapshot(tail)
+	assertCount(tail, false)
+
+	snapshot, count, changed = cl.Snapshot(0)
+	assertCount(tail, false)
+
+	tail = chunkSize / 2
+	snapshot, count, changed = cl.Snapshot(tail)
+	assertCount(tail, true)
+}

src/core.go

@@ -18,6 +18,28 @@ Matcher  -> EvtSearchFin      -> Terminal (update list)
 Matcher  -> EvtHeader         -> Terminal (update header)
 */
 
+type revision struct {
+	major int
+	minor int
+}
+
+func (r *revision) bumpMajor() {
+	r.major++
+	r.minor = 0
+}
+
+func (r *revision) bumpMinor() {
+	r.minor++
+}
+
+func (r revision) equals(other revision) bool {
+	return r.major == other.major && r.minor == other.minor
+}
+
+func (r revision) compatible(other revision) bool {
+	return r.major == other.major
+}
+
 // Run starts fzf
 func Run(opts *Options) (int, error) {
 	if opts.Tmux != nil && len(os.Getenv("TMUX")) > 0 && opts.Tmux.index >= opts.Height.index {
@@ -155,8 +177,8 @@ func Run(opts *Options) (int, error) {
 			opts.Fuzzy, opts.FuzzyAlgo, opts.Extended, opts.Case, opts.Normalize, forward, withPos,
 			opts.Filter == nil, opts.Nth, opts.Delimiter, runes)
 	}
-	inputRevision := 0
+	inputRevision := revision{}
-	snapshotRevision := 0
+	snapshotRevision := revision{}
 	matcher := NewMatcher(cache, patternBuilder, sort, opts.Tac, eventBox, inputRevision)
 
 	// Filtering mode
@@ -190,7 +212,8 @@ func Run(opts *Options) (int, error) {
 			eventBox.Unwatch(EvtReadNew)
 			eventBox.WaitFor(EvtReadFin)
 
-			snapshot, _ := chunkList.Snapshot()
+			// NOTE: Streaming filter is inherently not compatible with --tail
+			snapshot, _, _ := chunkList.Snapshot(opts.Tail)
 			merger, _ := matcher.scan(MatchRequest{
 				chunks:  snapshot,
 				pattern: pattern})
@@ -261,7 +284,7 @@ func Run(opts *Options) (int, error) {
 		reading = true
 		chunkList.Clear()
 		itemIndex = 0
-		inputRevision++
+		inputRevision.bumpMajor()
 		header = make([]string, 0, opts.HeaderLines)
 		go reader.restart(command, environ)
 	}
@@ -306,10 +329,14 @@ func Run(opts *Options) (int, error) {
 						useSnapshot = false
 					}
 					if !useSnapshot {
-						if snapshotRevision != inputRevision {
+						if !snapshotRevision.compatible(inputRevision) {
 							query = []rune{}
 						}
-						snapshot, count = chunkList.Snapshot()
+						var changed bool
+						snapshot, count, changed = chunkList.Snapshot(opts.Tail)
+						if changed {
+							inputRevision.bumpMinor()
+						}
 						snapshotRevision = inputRevision
 					}
 					total = count
@@ -349,7 +376,10 @@ func Run(opts *Options) (int, error) {
 						break
 					}
 					if !useSnapshot {
-						newSnapshot, newCount := chunkList.Snapshot()
+						newSnapshot, newCount, changed := chunkList.Snapshot(opts.Tail)
+						if changed {
+							inputRevision.bumpMinor()
+						}
 						// We want to avoid showing empty list when reload is triggered
 						// and the query string is changed at the same time i.e. command != nil && changed
 						if command == nil || newCount > 0 {

src/matcher.go

@@ -16,7 +16,7 @@ type MatchRequest struct {
 	pattern  *Pattern
 	final    bool
 	sort     bool
-	revision int
+	revision revision
 }
 
 // Matcher is responsible for performing search
@@ -30,7 +30,7 @@ type Matcher struct {
 	partitions     int
 	slab           []*util.Slab
 	mergerCache    map[string]*Merger
-	revision       int
+	revision       revision
 }
 
 const (
@@ -40,7 +40,7 @@ const (
 
 // NewMatcher returns a new Matcher
 func NewMatcher(cache *ChunkCache, patternBuilder func([]rune) *Pattern,
-	sort bool, tac bool, eventBox *util.EventBox, revision int) *Matcher {
+	sort bool, tac bool, eventBox *util.EventBox, revision revision) *Matcher {
 	partitions := util.Min(numPartitionsMultiplier*runtime.NumCPU(), maxPartitions)
 	return &Matcher{
 		cache:          cache,
@@ -82,11 +82,13 @@ func (m *Matcher) Loop() {
 			break
 		}
 
+		cacheCleared := false
 		if request.sort != m.sort || request.revision != m.revision {
 			m.sort = request.sort
 			m.revision = request.revision
 			m.mergerCache = make(map[string]*Merger)
 			m.cache.Clear()
+			cacheCleared = true
 		}
 
 		// Restart search
@@ -95,11 +97,10 @@ func (m *Matcher) Loop() {
 		cancelled := false
 		count := CountItems(request.chunks)
 
-		foundCache := false
+		if !cacheCleared {
 			if count == prevCount {
 				// Look up mergerCache
 				if cached, found := m.mergerCache[patternString]; found {
-				foundCache = true
 					merger = cached
 				}
 			} else {
@@ -107,8 +108,9 @@ func (m *Matcher) Loop() {
 				prevCount = count
 				m.mergerCache = make(map[string]*Merger)
 			}
+		}
 
-		if !foundCache {
+		if merger == nil {
 			merger, cancelled = m.scan(request)
 		}
 
@@ -160,6 +162,7 @@ func (m *Matcher) scan(request MatchRequest) (*Merger, bool) {
 		return PassMerger(&request.chunks, m.tac, request.revision), false
 	}
 
+	minIndex := request.chunks[0].items[0].Index()
 	cancelled := util.NewAtomicBool(false)
 
 	slices := m.sliceChunks(request.chunks)
@@ -231,11 +234,11 @@ func (m *Matcher) scan(request MatchRequest) (*Merger, bool) {
 		partialResult := <-resultChan
 		partialResults[partialResult.index] = partialResult.matches
 	}
-	return NewMerger(pattern, partialResults, m.sort, m.tac, request.revision), false
+	return NewMerger(pattern, partialResults, m.sort, m.tac, request.revision, minIndex), false
 }
 
 // Reset is called to interrupt/signal the ongoing search
-func (m *Matcher) Reset(chunks []*Chunk, patternRunes []rune, cancel bool, final bool, sort bool, revision int) {
+func (m *Matcher) Reset(chunks []*Chunk, patternRunes []rune, cancel bool, final bool, sort bool, revision revision) {
 	pattern := m.patternBuilder(patternRunes)
 
 	var event util.EventType

src/merger.go

@@ -3,8 +3,8 @@ package fzf
 import "fmt"
 
 // EmptyMerger is a Merger with no data
-func EmptyMerger(revision int) *Merger {
+func EmptyMerger(revision revision) *Merger {
-	return NewMerger(nil, [][]Result{}, false, false, revision)
+	return NewMerger(nil, [][]Result{}, false, false, revision, 0)
 }
 
 // Merger holds a set of locally sorted lists of items and provides the view of
@@ -20,19 +20,25 @@ type Merger struct {
 	final    bool
 	count    int
 	pass     bool
-	revision int
+	revision revision
+	minIndex int32
 }
 
 // PassMerger returns a new Merger that simply returns the items in the
 // original order
-func PassMerger(chunks *[]*Chunk, tac bool, revision int) *Merger {
+func PassMerger(chunks *[]*Chunk, tac bool, revision revision) *Merger {
+	var minIndex int32
+	if len(*chunks) > 0 {
+		minIndex = (*chunks)[0].items[0].Index()
+	}
 	mg := Merger{
 		pattern:  nil,
 		chunks:   chunks,
 		tac:      tac,
 		count:    0,
 		pass:     true,
-		revision: revision}
+		revision: revision,
+		minIndex: minIndex}
 
 	for _, chunk := range *mg.chunks {
 		mg.count += chunk.count
@@ -41,7 +47,7 @@ func PassMerger(chunks *[]*Chunk, tac bool, revision int) *Merger {
 }
 
 // NewMerger returns a new Merger
-func NewMerger(pattern *Pattern, lists [][]Result, sorted bool, tac bool, revision int) *Merger {
+func NewMerger(pattern *Pattern, lists [][]Result, sorted bool, tac bool, revision revision, minIndex int32) *Merger {
 	mg := Merger{
 		pattern:  pattern,
 		lists:    lists,
@@ -52,7 +58,8 @@ func NewMerger(pattern *Pattern, lists [][]Result, sorted bool, tac bool, revisi
 		tac:      tac,
 		final:    false,
 		count:    0,
-		revision: revision}
+		revision: revision,
+		minIndex: minIndex}
 
 	for _, list := range mg.lists {
 		mg.count += len(list)
@@ -61,7 +68,7 @@ func NewMerger(pattern *Pattern, lists [][]Result, sorted bool, tac bool, revisi
 }
 
 // Revision returns revision number
-func (mg *Merger) Revision() int {
+func (mg *Merger) Revision() revision {
 	return mg.revision
 }
 
@@ -81,7 +88,7 @@ func (mg *Merger) First() Result {
 func (mg *Merger) FindIndex(itemIndex int32) int {
 	index := -1
 	if mg.pass {
-		index = int(itemIndex)
+		index = int(itemIndex - mg.minIndex)
 		if mg.tac {
 			index = mg.count - index - 1
 		}
@@ -102,6 +109,13 @@ func (mg *Merger) Get(idx int) Result {
 		if mg.tac {
 			idx = mg.count - idx - 1
 		}
+		firstChunk := (*mg.chunks)[0]
+		if firstChunk.count < chunkSize && idx >= firstChunk.count {
+			idx -= firstChunk.count
+
+			chunk := (*mg.chunks)[idx/chunkSize+1]
+			return Result{item: &chunk.items[idx%chunkSize]}
+		}
 		chunk := (*mg.chunks)[idx/chunkSize]
 		return Result{item: &chunk.items[idx%chunkSize]}
 	}

src/merger_test.go

@@ -23,10 +23,11 @@ func randResult() Result {
 }
 
 func TestEmptyMerger(t *testing.T) {
-	assert(t, EmptyMerger(0).Length() == 0, "Not empty")
+	r := revision{}
-	assert(t, EmptyMerger(0).count == 0, "Invalid count")
+	assert(t, EmptyMerger(r).Length() == 0, "Not empty")
-	assert(t, len(EmptyMerger(0).lists) == 0, "Invalid lists")
+	assert(t, EmptyMerger(r).count == 0, "Invalid count")
-	assert(t, len(EmptyMerger(0).merged) == 0, "Invalid merged list")
+	assert(t, len(EmptyMerger(r).lists) == 0, "Invalid lists")
+	assert(t, len(EmptyMerger(r).merged) == 0, "Invalid merged list")
 }
 
 func buildLists(partiallySorted bool) ([][]Result, []Result) {
@@ -57,7 +58,7 @@ func TestMergerUnsorted(t *testing.T) {
 	cnt := len(items)
 
 	// Not sorted: same order
-	mg := NewMerger(nil, lists, false, false, 0)
+	mg := NewMerger(nil, lists, false, false, revision{}, 0)
 	assert(t, cnt == mg.Length(), "Invalid Length")
 	for i := 0; i < cnt; i++ {
 		assert(t, items[i] == mg.Get(i), "Invalid Get")
@@ -69,7 +70,7 @@ func TestMergerSorted(t *testing.T) {
 	cnt := len(items)
 
 	// Sorted sorted order
-	mg := NewMerger(nil, lists, true, false, 0)
+	mg := NewMerger(nil, lists, true, false, revision{}, 0)
 	assert(t, cnt == mg.Length(), "Invalid Length")
 	sort.Sort(ByRelevance(items))
 	for i := 0; i < cnt; i++ {
@@ -79,7 +80,7 @@ func TestMergerSorted(t *testing.T) {
 	}
 
 	// Inverse order
-	mg2 := NewMerger(nil, lists, true, false, 0)
+	mg2 := NewMerger(nil, lists, true, false, revision{}, 0)
 	for i := cnt - 1; i >= 0; i-- {
 		if items[i] != mg2.Get(i) {
 			t.Error("Not sorted", items[i], mg2.Get(i))

src/options.go

@@ -41,6 +41,7 @@ Usage: fzf [options]
                             field index expressions
     -d, --delimiter=STR     Field delimiter regex (default: AWK-style)
     +s, --no-sort           Do not sort the result
+    --tail=NUM              Maximum number of items to keep in memory
     --track                 Track the current selection when the result is updated
     --tac                   Reverse the order of the input
     --disabled              Do not perform search
@@ -421,6 +422,7 @@ type Options struct {
 	Sort         int
 	Track        trackOption
 	Tac          bool
+	Tail         int
 	Criteria     []criterion
 	Multi        int
 	Ansi         bool
@@ -2096,6 +2098,15 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 			opts.Tac = true
 		case "--no-tac":
 			opts.Tac = false
+		case "--tail":
+			if opts.Tail, err = nextInt(allArgs, &i, "number of items to keep required"); err != nil {
+				return err
+			}
+			if opts.Tail <= 0 {
+				return errors.New("number of items to keep must be a positive integer")
+			}
+		case "--no-tail":
+			opts.Tail = 0
 		case "-i", "--ignore-case":
 			opts.Case = CaseIgnore
 		case "+i", "--no-ignore-case":
@@ -2631,6 +2642,13 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 			} else if match, value := optString(arg, "--jump-labels="); match {
 				opts.JumpLabels = value
 				validateJumpLabels = true
+			} else if match, value := optString(arg, "--tail="); match {
+				if opts.Tail, err = atoi(value); err != nil {
+					return err
+				}
+				if opts.Tail <= 0 {
+					return errors.New("number of items to keep must be a positive integer")
+				}
 			} else {
 				return errors.New("unknown option: " + arg)
 			}

src/terminal.go

@@ -160,6 +160,7 @@ type itemLine struct {
 	result    Result
 	empty     bool
 	other     bool
+	minIndex  int32
 }
 
 func (t *Terminal) markEmptyLine(line int) {
@@ -301,7 +302,7 @@ type Terminal struct {
 	merger             *Merger
 	selected           map[int32]selectedItem
 	version            int64
-	revision           int
+	revision           revision
 	reqBox             *util.EventBox
 	initialPreviewOpts previewOpts
 	previewOpts        previewOpts
@@ -822,7 +823,7 @@ func NewTerminal(opts *Options, eventBox *util.EventBox, executor *util.Executor
 		printer:            opts.Printer,
 		printsep:           opts.PrintSep,
 		proxyScript:        opts.ProxyScript,
-		merger:             EmptyMerger(0),
+		merger:             EmptyMerger(revision{}),
 		selected:           make(map[int32]selectedItem),
 		reqBox:             util.NewEventBox(),
 		initialPreviewOpts: opts.Preview,
@@ -1164,8 +1165,8 @@ func (t *Terminal) UpdateProgress(progress float32) {
 func (t *Terminal) UpdateList(merger *Merger, triggerResultEvent bool) {
 	t.mutex.Lock()
 	prevIndex := minItem.Index()
-	reset := t.revision != merger.Revision()
+	newRevision := merger.Revision()
-	if !reset && t.track != trackDisabled {
+	if t.revision.compatible(newRevision) && t.track != trackDisabled {
 		if t.merger.Length() > 0 {
 			prevIndex = t.currentIndex()
 		} else if merger.Length() > 0 {
@@ -1174,9 +1175,19 @@ func (t *Terminal) UpdateList(merger *Merger, triggerResultEvent bool) {
 	}
 	t.progress = 100
 	t.merger = merger
-	if reset {
+	if !t.revision.equals(newRevision) {
+		if !t.revision.compatible(newRevision) { // Reloaded: clear selection
 			t.selected = make(map[int32]selectedItem)
-		t.revision = merger.Revision()
+		} else { // Trimmed by --tail: filter selection by index
+			filtered := make(map[int32]selectedItem)
+			for k, v := range t.selected {
+				if k >= merger.minIndex {
+					filtered[k] = v
+				}
+			}
+			t.selected = filtered
+		}
+		t.revision = newRevision
 		t.version++
 	}
 	if t.triggerLoad {
@@ -1959,9 +1970,9 @@ func (t *Terminal) printItem(result Result, line int, maxLine int, index int, cu
 
 	// Avoid unnecessary redraw
 	newLine := itemLine{firstLine: line, cy: index + t.offset, current: current, selected: selected, label: label,
-		result: result, queryLen: len(t.input), width: 0, hasBar: line >= barRange[0] && line < barRange[1]}
+		result: result, queryLen: len(t.input), width: 0, hasBar: line >= barRange[0] && line < barRange[1], minIndex: t.merger.minIndex}
 	prevLine := t.prevLines[line]
-	forceRedraw := prevLine.other || prevLine.firstLine != newLine.firstLine
+	forceRedraw := prevLine.other || prevLine.firstLine != newLine.firstLine || prevLine.minIndex != t.merger.minIndex
 	printBar := func(lineNum int, forceRedraw bool) bool {
 		return t.printBar(lineNum, forceRedraw, barRange)
 	}