Fix debounce fails

debounce/simple_debouncer.go

@@ -1,25 +1,34 @@
 package debounce
 
-// SimpleDebouncer debounce function call with simple logc:
-// 1. If call is currently pending, function call should go through
-// 2. If call is scheduled, but not pending, function call should be voided
+import (
+	"sync"
+	"sync/atomic"
+)
+
+// SimpleDebouncer is are tool for queuing immutable functions calls. It provides:
+// 1. Blocking simultaneous calls
+// 2. If there is no running call and no waiting call, then the current call go through
+// 3. If there is running call and no waiting call, then the current call go waiting
+// 4. If there is running call and waiting call, then the current call are voided
 type SimpleDebouncer struct {
-	channel chan struct{}
+	m     sync.Mutex
+	count atomic.Int32
 }
 
-// NewDebouncer creates a new Debouncer with a buffered channel of size 1
+// NewSimpleDebouncer creates a new SimpleDebouncer.
 func NewSimpleDebouncer() *SimpleDebouncer {
-	return &SimpleDebouncer{
-		channel: make(chan struct{}, 1),
-	}
+	return &SimpleDebouncer{}
 }
 
-// Debounce attempts to execute the function if the channel allows it
-func (d *SimpleDebouncer) Debounce(fn func()) {
-	select {
-	case d.channel <- struct{}{}:
-		fn()
-		<-d.channel
-	default:
+// Debounce attempts to execute the function if the logic of the SimpleDebouncer allows it.
+func (d *SimpleDebouncer) Debounce(fn func()) bool {
+	if d.count.Add(1) > 2 {
+		d.count.Add(-1)
+		return false
 	}
+	d.m.Lock()
+	fn()
+	d.count.Add(-1)
+	d.m.Unlock()
+	return true
 }

debounce/simple_debouncer_test.go

@@ -5,17 +5,154 @@ package debounce
 
 import (
 	"runtime"
+	"sync"
 	"sync/atomic"
 	"testing"
+	"time"
 )
 
+// TestSimpleDebouncerRace tests SimpleDebouncer for the fact that it does not allow concurrent writing, reading.
+func TestSimpleDebouncerRace(t *testing.T) {
+	operations := 1000
+	runs := 100
+	count := 3
+
+	d := NewSimpleDebouncer()
+	for r := 0; r < runs; r++ {
+		var counter atomic.Int32
+		var wg sync.WaitGroup
+		wg.Add(count)
+
+		results := make([]bool, count)
+		fails := make([]bool, count)
+		for c := range results {
+			result := &results[c]
+			fail := &fails[c]
+
+			go func() {
+				*result = d.Debounce(func() {
+					for i := 0; i < operations; i++ {
+						if counter.Add(1) != 1 {
+							*fail = true
+						}
+						time.Sleep(time.Microsecond)
+						counter.Add(-1)
+					}
+				})
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+
+		// check results
+
+		finished := 0
+		for i, done := range results {
+			if done {
+				finished++
+			}
+			if fails[i] {
+				t.Fatalf("Simultaneous execution detected")
+			}
+		}
+		if finished < 2 {
+			t.Fatalf("In one run should be finished more than 2 `Debounce` method calls, but finished %d", finished)
+		}
+	}
+}
+
+// TestDebouncerExtreme tests SimpleDebouncer in the conditions  fast multi `Debounce` method calls and fast execution of the `debounced function`.
+func TestDebouncerExtreme(t *testing.T) {
+	type runResult struct {
+		executedN int32
+		done      bool
+	}
+
+	runs := 10000
+	count := 20
+
+	d := NewSimpleDebouncer()
+	var wg sync.WaitGroup
+	for r := 0; r < runs; r++ {
+		var executionsC atomic.Int32
+		wg.Add(count)
+
+		results := make([]runResult, count)
+
+		for c := range results {
+			result := &results[c]
+
+			go func() {
+				result.done = d.Debounce(func() {
+					result.executedN = executionsC.Add(1)
+				})
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+
+		// check results
+		finished := 0
+		for _, result := range results {
+			if result.done {
+				if result.executedN == 0 {
+					t.Fatalf("Wrong execution detected: \n%#v", result)
+				}
+				finished++
+			}
+		}
+		if finished < 2 {
+			t.Fatalf("In one run should be finished more than 2 `Debounce` method calls, but finished %d", finished)
+		}
+	}
+}
+
+// TestSimpleDebouncerCount tests SimpleDebouncer for the fact that it pended only one function call.
+func TestSimpleDebouncerCount(t *testing.T) {
+	calls := 10
+
+	// Subtracting a one call that will be performed directly (not through goroutines)
+	calls--
+
+	d := NewSimpleDebouncer()
+	var prepared, start, done sync.WaitGroup
+	prepared.Add(calls)
+	start.Add(1)
+	done.Add(calls)
+
+	finished := 0
+	for c := 0; c < calls; c++ {
+		go func() {
+			prepared.Done()
+			start.Wait()
+			d.Debounce(func() {
+				finished++
+			})
+			done.Done()
+		}()
+	}
+	d.Debounce(func() {
+		prepared.Wait()
+		start.Done()
+		finished++
+		time.Sleep(time.Second)
+	})
+	done.Wait()
+
+	// check results
+	if finished != 2 {
+		t.Fatalf("Should be finished 2 `Debounce` method calls, but finished %d", finished)
+	}
+}
+
 // TestDebouncer tests that the debouncer allows only one function to execute at a time
 func TestSimpleDebouncer(t *testing.T) {
 	t.Skip("This test sometimes ends vai panic. Issue https://github.com/scylladb/gocql/pull/344")
 	d := NewSimpleDebouncer()
 	var executions int32
 	startedCh := make(chan struct{}, 1)
 	doneCh := make(chan struct{}, 1)
+
 	// Function to increment executions
 	fn := func() {
 		<-startedCh // Simulate work