Added 'resize' operation to BoundedQueue

Signed-off-by: Juraci Paixão Kröhling <juraci@kroehling.de>

pkg/queue/bounded_queue.go

@@ -19,6 +19,7 @@ import (
 	"sync"
 	"sync/atomic"
 	"time"
+	"unsafe"
 
 	"github.com/uber/jaeger-lib/metrics"
 )
@@ -29,46 +30,55 @@ import (
 // channels, with a special Reaper goroutine that wakes up when the queue is full and consumers
 // the items from the top of the queue until its size drops back to maxSize
 type BoundedQueue struct {
-	capacity      int
 	size          int32
 	onDroppedItem func(item interface{})
-	items         chan interface{}
+	items         *chan interface{}
 	stopCh        chan struct{}
 	stopWG        sync.WaitGroup
 	stopped       int32
+	consumer      func(item interface{})
+	workers       int
 }
 
 // NewBoundedQueue constructs the new queue of specified capacity, and with an optional
 // callback for dropped items (e.g. useful to emit metrics).
 func NewBoundedQueue(capacity int, onDroppedItem func(item interface{})) *BoundedQueue {
+	queue := make(chan interface{}, capacity)
 	return &BoundedQueue{
-		capacity:      capacity,
 		onDroppedItem: onDroppedItem,
-		items:         make(chan interface{}, capacity),
+		items:         &queue,
 		stopCh:        make(chan struct{}),
 	}
 }
 
 // StartConsumers starts a given number of goroutines consuming items from the queue
 // and passing them into the consumer callback.
 func (q *BoundedQueue) StartConsumers(num int, consumer func(item interface{})) {
+	q.workers = num
+	q.consumer = consumer
 	var startWG sync.WaitGroup
-	for i := 0; i < num; i++ {
+	for i := 0; i < q.workers; i++ {
 		q.stopWG.Add(1)
 		startWG.Add(1)
-		go func() {
+		go func(queue chan interface{}) {
 			startWG.Done()
 			defer q.stopWG.Done()
 			for {
 				select {
-				case item := <-q.items:
-					atomic.AddInt32(&q.size, -1)
-					consumer(item)
+				case item, ok := <-queue:
+					if ok {
+						atomic.AddInt32(&q.size, -1)
+						q.consumer(item)
+					} else {
+						// channel closed, finish worker
+						return
+					}
 				case <-q.stopCh:
+					// the whole queue is closing, finish worker
 					return
 				}
 			}
-		}()
+		}(*q.items)
 	}
 	startWG.Wait()
 }
@@ -79,11 +89,23 @@ func (q *BoundedQueue) Produce(item interface{}) bool {
 		q.onDroppedItem(item)
 		return false
 	}
+
+	// we might have two concurrent backing queues at the moment
+	// their combined size is stored in q.size, and their combined capacity
+	// should match the capacity of the new queue
+	if atomic.LoadInt32(&q.size) >= int32(q.Capacity()) && q.Capacity() > 0 {
+		// current consumers of the queue (like tests) expect the queue capacity = 0 to work
+		// so, we don't drop items when the capacity is 0
+		q.onDroppedItem(item)
+		return false
+	}
+
 	select {
-	case q.items <- item:
+	case *q.items <- item:
 		atomic.AddInt32(&q.size, 1)
 		return true
 	default:
+		// should not happen, as overflows should have been captured earlier
 		if q.onDroppedItem != nil {
 			q.onDroppedItem(item)
 		}
@@ -97,7 +119,7 @@ func (q *BoundedQueue) Stop() {
 	atomic.StoreInt32(&q.stopped, 1) // disable producer
 	close(q.stopCh)
 	q.stopWG.Wait()
-	close(q.items)
+	close(*q.items)
 }
 
 // Size returns the current size of the queue
@@ -107,7 +129,7 @@ func (q *BoundedQueue) Size() int {
 
 // Capacity returns capacity of the queue
 func (q *BoundedQueue) Capacity() int {
-	return q.capacity
+	return cap(*q.items)
 }
 
 // StartLengthReporting starts a timer-based goroutine that periodically reports
@@ -127,3 +149,27 @@ func (q *BoundedQueue) StartLengthReporting(reportPeriod time.Duration, gauge me
 		}
 	}()
 }
+
+// Resize changes the capacity of the queue, returning whether the action was successful
+func (q *BoundedQueue) Resize(capacity int) bool {
+	if capacity == cap(*q.items) {
+		// noop
+		return false
+	}
+
+	previous := *q.items
+	queue := make(chan interface{}, capacity)
+
+	// swap queues
+	// #nosec
+	swapped := atomic.CompareAndSwapPointer((*unsafe.Pointer)(unsafe.Pointer(&q.items)), unsafe.Pointer(q.items), unsafe.Pointer(&queue))
+	if swapped {
+		// start a new set of consumers, based on the information given previously
+		q.StartConsumers(q.workers, q.consumer)
+
+		// gracefully drain the existing queue
+		close(previous)
+	}
+
+	return swapped
+}

pkg/queue/bounded_queue_test.go

@@ -16,6 +16,7 @@
 package queue
 
 import (
+	"fmt"
 	"reflect"
 	"sync"
 	"sync/atomic"
@@ -156,3 +157,173 @@ func (s *consumerState) assertConsumed(expected map[string]bool) {
 	}
 	assert.Equal(s.t, expected, s.snapshot())
 }
+
+func TestResizeUp(t *testing.T) {
+	q := NewBoundedQueue(2, func(item interface{}) {
+		fmt.Printf("dropped: %v\n", item)
+	})
+
+	var firstConsumer, secondConsumer, releaseConsumers sync.WaitGroup
+	firstConsumer.Add(1)
+	secondConsumer.Add(1)
+	releaseConsumers.Add(1)
+
+	released, resized := false, false
+	q.StartConsumers(1, func(item interface{}) {
+		if !resized { // we'll have a second consumer once the queue is resized
+			// signal that the worker is processing
+			firstConsumer.Done()
+		} else {
+			// once we release the lock, we might end up with multiple calls to reach this
+			if !released {
+				secondConsumer.Done()
+			}
+		}
+
+		// wait until we are signaled that we can finish
+		releaseConsumers.Wait()
+	})
+
+	assert.True(t, q.Produce("a")) // in process
+	firstConsumer.Wait()
+
+	assert.True(t, q.Produce("b"))  // in queue
+	assert.True(t, q.Produce("c"))  // in queue
+	assert.False(t, q.Produce("d")) // dropped
+	assert.EqualValues(t, 2, q.Capacity())
+	assert.EqualValues(t, q.Capacity(), q.Size())
+	assert.EqualValues(t, q.Capacity(), len(*q.items))
+
+	resized = true
+	assert.True(t, q.Resize(4))
+	assert.True(t, q.Produce("e")) // in process by the second consumer
+	secondConsumer.Wait()
+
+	assert.True(t, q.Produce("f"))  // in the new queue
+	assert.True(t, q.Produce("g"))  // in the new queue
+	assert.False(t, q.Produce("h")) // the new queue has the capacity, but the sum of queues doesn't
+
+	assert.EqualValues(t, 4, q.Capacity())
+	assert.EqualValues(t, q.Capacity(), q.Size()) // the combined queues are at the capacity right now
+	assert.EqualValues(t, 2, len(*q.items))       // the new internal queue should have two items only
+
+	released = true
+	releaseConsumers.Done()
+}
+
+func TestResizeDown(t *testing.T) {
+	q := NewBoundedQueue(4, func(item interface{}) {
+		fmt.Printf("dropped: %v\n", item)
+	})
+
+	var consumer, releaseConsumers sync.WaitGroup
+	consumer.Add(1)
+	releaseConsumers.Add(1)
+
+	released := false
+	q.StartConsumers(1, func(item interface{}) {
+		// once we release the lock, we might end up with multiple calls to reach this
+		if !released {
+			// signal that the worker is processing
+			consumer.Done()
+		}
+
+		// wait until we are signaled that we can finish
+		releaseConsumers.Wait()
+	})
+
+	assert.True(t, q.Produce("a")) // in process
+	consumer.Wait()
+
+	assert.True(t, q.Produce("b")) // in queue
+	assert.True(t, q.Produce("c")) // in queue
+	assert.True(t, q.Produce("d")) // in queue
+	assert.True(t, q.Produce("e")) // dropped
+	assert.EqualValues(t, 4, q.Capacity())
+	assert.EqualValues(t, q.Capacity(), q.Size())
+	assert.EqualValues(t, q.Capacity(), len(*q.items))
+
+	assert.True(t, q.Resize(2))
+	assert.False(t, q.Produce("f")) // dropped
+
+	assert.EqualValues(t, 2, q.Capacity())
+	assert.EqualValues(t, 4, q.Size())      // the queue will eventually drain, but it will live for a while over capacity
+	assert.EqualValues(t, 0, len(*q.items)) // the new queue is empty, as the old queue is still full and over capacity
+
+	released = true
+	releaseConsumers.Done()
+}
+
+func TestResizeOldQueueIsDrained(t *testing.T) {
+	q := NewBoundedQueue(2, func(item interface{}) {
+		fmt.Printf("dropped: %v\n", item)
+	})
+
+	var consumerReady, consumed, readyToConsume sync.WaitGroup
+	consumerReady.Add(1)
+	readyToConsume.Add(1)
+	consumed.Add(5) // we expect 5 items to be processed
+
+	first := true
+	q.StartConsumers(1, func(item interface{}) {
+		// first run only
+		if first {
+			first = false
+			consumerReady.Done()
+		}
+
+		readyToConsume.Wait()
+		consumed.Done()
+	})
+
+	assert.True(t, q.Produce("a"))
+	consumerReady.Wait()
+
+	assert.True(t, q.Produce("b"))
+	assert.True(t, q.Produce("c"))
+	assert.False(t, q.Produce("d"))
+
+	q.Resize(4)
+
+	assert.True(t, q.Produce("e"))
+	assert.True(t, q.Produce("f"))
+	assert.False(t, q.Produce("g"))
+
+	readyToConsume.Done()
+	consumed.Wait() // once this returns, we've consumed all items, meaning that both queues are drained
+}
+
+func TestNoopResize(t *testing.T) {
+	q := NewBoundedQueue(2, func(item interface{}) {
+	})
+
+	assert.False(t, q.Resize(2))
+}
+
+func TestZeroSize(t *testing.T) {
+	q := NewBoundedQueue(0, func(item interface{}) {
+	})
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+	q.StartConsumers(1, func(item interface{}) {
+		wg.Done()
+	})
+
+	assert.True(t, q.Produce("a")) // in process
+	wg.Wait()
+
+	// if we didn't finish with a timeout, then we are good
+}
+
+func BenchmarkBoundedQueue(b *testing.B) {
+	q := NewBoundedQueue(1000, func(item interface{}) {
+	})
+
+	q.StartConsumers(10, func(item interface{}) {
+	})
+
+	for n := 0; n < b.N; n++ {
+		q.Produce(n)
+	}
+}