From 2f9df911718b13ca86386d0a95016c17bd45d0da Mon Sep 17 00:00:00 2001
From: Junegunn Choi <junegunn.c@gmail.com>
Date: Thu, 26 Feb 2026 14:51:59 +0900
Subject: [PATCH] Add --threads option to control matcher concurrency

By default, fzf uses 8 * NumCPU goroutines (capped at 32) for
parallel matching. --threads N overrides this to use exactly N
goroutines, which is useful for benchmarking and profiling.
---
 src/core.go    | 2 +-
 src/matcher.go | 5 ++++-
 src/options.go | 8 ++++++++
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/core.go b/src/core.go
index 6c453082..3d31bed9 100644
--- a/src/core.go
+++ b/src/core.go
@@ -235,7 +235,7 @@ func Run(opts *Options) (int, error) {
 			opts.Fuzzy, opts.FuzzyAlgo, opts.Extended, opts.Case, opts.Normalize, forward, withPos,
 			opts.Filter == nil, nth, opts.Delimiter, inputRevision, runes, denylistCopy, headerLines)
 	}
-	matcher := NewMatcher(cache, patternBuilder, sort, opts.Tac, eventBox, inputRevision)
+	matcher := NewMatcher(cache, patternBuilder, sort, opts.Tac, eventBox, inputRevision, opts.Threads)
 
 	// Filtering mode
 	if opts.Filter != nil {
diff --git a/src/matcher.go b/src/matcher.go
index eb22abd8..14af1088 100644
--- a/src/matcher.go
+++ b/src/matcher.go
@@ -54,8 +54,11 @@ const (
 
 // NewMatcher returns a new Matcher
 func NewMatcher(cache *ChunkCache, patternBuilder func([]rune) *Pattern,
-	sort bool, tac bool, eventBox *util.EventBox, revision revision) *Matcher {
+	sort bool, tac bool, eventBox *util.EventBox, revision revision, threads int) *Matcher {
 	partitions := min(numPartitionsMultiplier*runtime.NumCPU(), maxPartitions)
+	if threads > 0 {
+		partitions = threads
+	}
 	return &Matcher{
 		cache:          cache,
 		patternBuilder: patternBuilder,
diff --git a/src/options.go b/src/options.go
index fc055968..ba314c05 100644
--- a/src/options.go
+++ b/src/options.go
@@ -678,6 +678,7 @@ type Options struct {
 	WalkerSkip        []string
 	Version           bool
 	Help              bool
+	Threads           int
 	Bench             time.Duration
 	CPUProfile        string
 	MEMProfile        string
@@ -3375,6 +3376,13 @@ func parseOptions(index *int, opts *Options, allArgs []string) error {
 				return err
 			}
 			opts.WalkerSkip = filterNonEmpty(strings.Split(str, ","))
+		case "--threads":
+			if opts.Threads, err = nextInt("number of threads required"); err != nil {
+				return err
+			}
+			if opts.Threads < 0 {
+				return errors.New("--threads must be a positive integer")
+			}
 		case "--bench":
 			str, err := nextString("duration required (e.g. 3s, 500ms)")
 			if err != nil {