Add MinWorkers option

pond.go

@@ -16,6 +16,16 @@ func defaultPanicHandler(panic interface{}) {
 	fmt.Printf("Worker exits from a panic: %v\nStack trace: %s\n", panic, string(debug.Stack()))
 }
 
+func linearGrowthFn(workerCount, minWorkers, maxWorkers int) int {
+	if workerCount < minWorkers {
+		return minWorkers
+	}
+	if workerCount < maxWorkers {
+		return 1
+	}
+	return 0
+}
+
 // Option represents an option that can be passed when building a worker pool to customize it
 type Option func(*WorkerPool)
 
@@ -33,8 +43,16 @@ func PanicHandler(panicHandler func(interface{})) Option {
 	}
 }
 
+// MinWorkers allows to change the minimum number of workers of a worker pool
+func MinWorkers(minWorkers int) Option {
+	return func(pool *WorkerPool) {
+		pool.minWorkers = minWorkers
+	}
+}
+
 // WorkerPool models a pool of workers
 type WorkerPool struct {
+	minWorkers      int
 	maxWorkers      int
 	maxCapacity     int
 	idleTimeout     time.Duration
@@ -45,6 +63,7 @@ type WorkerPool struct {
 	stopOnce        sync.Once
 	waitGroup       sync.WaitGroup
 	panicHandler    func(interface{})
+	growthFn        func(int, int, int) int
 }
 
 // New creates a worker pool with that can scale up to the given number of workers and capacity
@@ -58,6 +77,7 @@ func New(maxWorkers, maxCapacity int, options ...Option) *WorkerPool {
 		dispatchedTasks: make(chan func(), maxWorkers),
 		purgerQuit:      make(chan struct{}),
 		panicHandler:    defaultPanicHandler,
+		growthFn:        linearGrowthFn,
 	}
 
 	// Apply all options
@@ -65,6 +85,14 @@ func New(maxWorkers, maxCapacity int, options ...Option) *WorkerPool {
 		opt(pool)
 	}
 
+	// Make sure options are consistent
+	if pool.maxWorkers <= 0 {
+		pool.maxWorkers = 1
+	}
+	if pool.minWorkers > pool.maxWorkers {
+		pool.minWorkers = pool.maxWorkers
+	}
+
 	// Start dispatcher goroutine
 	pool.waitGroup.Add(1)
 	go func() {
@@ -81,6 +109,11 @@ func New(maxWorkers, maxCapacity int, options ...Option) *WorkerPool {
 		pool.purge()
 	}()
 
+	// Start minWorkers workers
+	if pool.minWorkers > 0 {
+		pool.startWorkers()
+	}
+
 	return pool
 }
 
@@ -138,12 +171,12 @@ func (p *WorkerPool) dispatch() {
 		// Attempt to submit the task to a worker without blocking
 		case p.dispatchedTasks <- task:
 			if p.Running() == 0 {
-				p.startWorker()
+				p.startWorkers()
 			}
 		default:
 			// Create a new worker if we haven't reached the limit yet
 			if p.Running() < p.maxWorkers {
-				p.startWorker()
+				p.startWorkers()
 			}
 
 			// Block until a worker accepts this task
@@ -167,7 +200,7 @@ func (p *WorkerPool) purge() {
 		select {
 		// Timed out waiting for any activity to happen, attempt to stop an idle worker
 		case <-ticker.C:
-			if p.Running() > 0 {
+			if p.Running() > p.minWorkers {
 				select {
 				case p.dispatchedTasks <- nil:
 				default:
@@ -182,13 +215,22 @@ func (p *WorkerPool) purge() {
 	}
 }
 
-func (p *WorkerPool) startWorker() {
+func (p *WorkerPool) startWorkers() {
+
+	count := p.growthFn(p.Running(), p.minWorkers, p.maxWorkers)
+
+	if count == 0 {
+		return
+	}
+
 	// Increment worker count
-	atomic.AddInt32(&p.workerCount, 1)
+	atomic.AddInt32(&p.workerCount, int32(count))
 
 	// Increment waiting group semaphore
-	p.waitGroup.Add(1)
+	p.waitGroup.Add(count)
 
+	//go func() {
+	for i := 0; i < count; i++ {
 		worker(p.dispatchedTasks, func() {
 
 			// Decrement worker count
@@ -198,6 +240,9 @@ func (p *WorkerPool) startWorker() {
 			p.waitGroup.Done()
 
 		}, p.panicHandler)
+	}
+	//}()
+
 }
 
 // Stop causes this pool to stop accepting tasks, without waiting for goroutines to exit

pond_benchmark_test.go

@@ -11,9 +11,9 @@ import (
 )
 
 const (
-	taskCount    = 1000000
+	taskCount    = 10000
-	taskDuration = 10 * time.Millisecond
+	taskDuration = 1 * time.Millisecond
-	workerCount  = 200000
+	workerCount  = 100
 )
 
 func BenchmarkPond(b *testing.B) {
@@ -36,6 +36,26 @@ func BenchmarkPond(b *testing.B) {
 	b.StopTimer()
 }
 
+func BenchmarkPondMinWorkers(b *testing.B) {
+	var wg sync.WaitGroup
+	pool := pond.New(workerCount, taskCount, pond.MinWorkers(workerCount))
+	defer pool.StopAndWait()
+
+	// Submit tasks
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		wg.Add(taskCount)
+		for i := 0; i < taskCount; i++ {
+			pool.Submit(func() {
+				time.Sleep(taskDuration)
+				wg.Done()
+			})
+		}
+		wg.Wait()
+	}
+	b.StopTimer()
+}
+
 func BenchmarkPondGroup(b *testing.B) {
 	pool := pond.New(workerCount, taskCount)
 	defer pool.StopAndWait()
@@ -72,6 +92,64 @@ func BenchmarkGoroutines(b *testing.B) {
 	b.StopTimer()
 }
 
+func BenchmarkGoroutinePool(b *testing.B) {
+	var wg sync.WaitGroup
+
+	// Submit tasks
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		taskChan := make(chan func())
+		wg.Add(workerCount)
+		// Start worker goroutines
+		for i := 0; i < workerCount; i++ {
+			go func() {
+				for task := range taskChan {
+					task()
+				}
+				wg.Done()
+			}()
+		}
+		// Submit tasks
+		for i := 0; i < taskCount; i++ {
+			taskChan <- func() {
+				time.Sleep(taskDuration)
+			}
+		}
+		close(taskChan)
+		wg.Wait()
+	}
+	b.StopTimer()
+}
+
+func BenchmarkBufferedGoroutinePool(b *testing.B) {
+	var wg sync.WaitGroup
+
+	// Submit tasks
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		taskChan := make(chan func(), taskCount)
+		wg.Add(workerCount)
+		// Start worker goroutines
+		for i := 0; i < workerCount; i++ {
+			go func() {
+				for task := range taskChan {
+					task()
+				}
+				wg.Done()
+			}()
+		}
+		// Submit tasks
+		for i := 0; i < taskCount; i++ {
+			taskChan <- func() {
+				time.Sleep(taskDuration)
+			}
+		}
+		close(taskChan)
+		wg.Wait()
+	}
+	b.StopTimer()
+}
+
 func BenchmarkGammazeroWorkerpool(b *testing.B) {
 	var wg sync.WaitGroup
 	wp := workerpool.New(workerCount)

pond_test.go

@@ -209,7 +209,7 @@ func TestSubmitWithPanic(t *testing.T) {
 	assert.Equal(int32(1), atomic.LoadInt32(&doneCount))
 }
 
-func TestSubmitWithIdleTimeout(t *testing.T) {
+func TestPoolWithCustomIdleTimeout(t *testing.T) {
 
 	assert := assert.New(t)
 
@@ -242,7 +242,7 @@ func TestSubmitWithIdleTimeout(t *testing.T) {
 	pool.StopAndWait()
 }
 
-func TestSubmitWithPanicHandler(t *testing.T) {
+func TestPoolWithCustomPanicHandler(t *testing.T) {
 
 	assert := assert.New(t)
 
@@ -264,6 +264,32 @@ func TestSubmitWithPanicHandler(t *testing.T) {
 	assert.Equal("panic now!", capturedPanic)
 }
 
+func TestPoolWithCustomMinWorkers(t *testing.T) {
+
+	assert := assert.New(t)
+
+	pool := pond.New(10, 5, pond.MinWorkers(10))
+
+	// Submit a task that panics
+	started := make(chan struct{})
+	completed := make(chan struct{})
+	pool.Submit(func() {
+		<-started
+		completed <- struct{}{}
+	})
+
+	started <- struct{}{}
+
+	// 10 workers should have been started
+	assert.Equal(10, pool.Running())
+
+	<-completed
+
+	pool.StopAndWait()
+
+	assert.Equal(0, pool.Running())
+}
+
 func TestGroupSubmit(t *testing.T) {
 
 	assert := assert.New(t)