From d3bcc30a8f6b945e44718cb420ac2061374f6346 Mon Sep 17 00:00:00 2001
From: Nedyalko Dyakov <nedyalko.dyakov@gmail.com>
Date: Tue, 11 Nov 2025 00:16:27 +0200
Subject: [PATCH] use sync.Cond

---
 autopipeline.go | 52 +++++++++++++++++++++----------------------------
 1 file changed, 22 insertions(+), 30 deletions(-)

diff --git a/autopipeline.go b/autopipeline.go
index 41e5bfc2..46e98a57 100644
--- a/autopipeline.go
+++ b/autopipeline.go
@@ -185,7 +185,7 @@ type AutoPipeliner struct {
 	queueLen atomic.Int32 // Fast path check without lock
 
 	// Flush control
-	flushCh chan struct{} // Signal to flush immediately
+	flushCond *sync.Cond // Condition variable to signal flusher
 
 	// Concurrency control
 	sem *internal.FastSemaphore // Semaphore for concurrent batch limit
@@ -219,12 +219,15 @@ func NewAutoPipeliner(pipeliner cmdableClient, config *AutoPipelineConfig) *Auto
 	ap := &AutoPipeliner{
 		pipeliner: pipeliner,
 		config:    config,
-		flushCh:   make(chan struct{}, 1),
 		sem:       internal.NewFastSemaphore(int32(config.MaxConcurrentBatches)),
 		ctx:       ctx,
 		cancel:    cancel,
 	}
 
+	// Initialize condition variable for flush signaling
+	// Use a separate mutex for the condition variable to avoid contention with queue operations
+	ap.flushCond = sync.NewCond(&sync.Mutex{})
+
 	// Initialize cmdable to route all commands through processAndBlock
 	ap.cmdable = ap.processAndBlock
 
@@ -323,11 +326,8 @@ func (ap *AutoPipeliner) processWithQueuedCmd(ctx context.Context, cmd Cmder) *q
 		ap.queueLen.Store(int32(queueLen))
 		ap.mu.Unlock()
 
-		// Always signal the flusher (non-blocking)
-		select {
-		case ap.flushCh <- struct{}{}:
-		default:
-		}
+		// Signal the flusher using condition variable
+		ap.flushCond.Signal()
 		return qc
 	}
 
@@ -338,11 +338,8 @@ func (ap *AutoPipeliner) processWithQueuedCmd(ctx context.Context, cmd Cmder) *q
 	ap.queueLen.Store(int32(queueLen))
 	ap.mu.Unlock()
 
-	// always signal the flusher (non-blocking)
-	select {
-	case ap.flushCh <- struct{}{}:
-	default:
-	}
+	// Signal the flusher using condition variable
+	ap.flushCond.Signal()
 	return qc
 }
 
@@ -360,6 +357,9 @@ func (ap *AutoPipeliner) Close() error {
 	// Cancel context to stop flusher
 	ap.cancel()
 
+	// Signal the flusher to wake up and check context
+	ap.flushCond.Signal()
+
 	// Wait for flusher to finish
 	ap.wg.Wait()
 
@@ -372,30 +372,22 @@ func (ap *AutoPipeliner) Close() error {
 // flusher is the background goroutine that flushes batches.
 func (ap *AutoPipeliner) flusher() {
 	defer ap.wg.Done()
+
 	for {
-		// Wait for a command to arrive
-		select {
-		case <-ap.flushCh:
-			// Command arrived, continue
-		case <-ap.ctx.Done():
+		// Wait for a command to arrive using condition variable
+		ap.flushCond.L.Lock()
+		for ap.Len() == 0 && ap.ctx.Err() == nil {
+			ap.flushCond.Wait()
+		}
+		ap.flushCond.L.Unlock()
+
+		// Check if context is cancelled
+		if ap.ctx.Err() != nil {
 			// Final flush before shutdown
 			ap.flushBatchSlice()
 			return
 		}
 
-		// Drain any additional signals
-		for {
-			select {
-			case <-ap.flushCh:
-				if ap.Len() >= ap.config.MaxBatchSize {
-					goto drained
-				}
-			default:
-				goto drained
-			}
-		}
-	drained:
-
 		// Flush all pending commands
 		for ap.Len() > 0 {
 			select {