fix: refactor priority ordered task queue implementation

internal/queue/genheap.go

@@ -0,0 +1,42 @@
+package queue
+
+// genericHeap is a generic heap implementation that can be used with any type that satisfies the constraints.Ordered interface.
+type genericHeap[T comparable[T]] []T
+
+func (h genericHeap[T]) Len() int {
+	return len(h)
+}
+
+func (h genericHeap[T]) Swap(i, j int) {
+	h[i], h[j] = h[j], h[i]
+}
+
+// Push pushes an element onto the heap. Do not call directly, use heap.Push
+func (h *genericHeap[T]) Push(x interface{}) {
+	*h = append(*h, x.(T))
+}
+
+// Pop pops an element from the heap. Do not call directly, use heap.Pop
+func (h *genericHeap[T]) Pop() interface{} {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+func (h genericHeap[T]) Peek() T {
+	if len(h) == 0 {
+		var zero T
+		return zero
+	}
+	return h[0]
+}
+
+func (h genericHeap[T]) Less(i, j int) bool {
+	return h[i].Less(h[j])
+}
+
+type comparable[T any] interface {
+	Less(other T) bool
+}

internal/queue/genheap_test.go

@@ -0,0 +1,48 @@
+package queue
+
+import (
+	"container/heap"
+	"testing"
+)
+
+type val struct {
+	v int
+}
+
+func (v val) Less(other val) bool {
+	return v.v < other.v
+}
+
+func TestGenericHeapInit(t *testing.T) {
+	genHeap := genericHeap[val]{{v: 3}, {v: 2}, {v: 1}}
+	heap.Init(&genHeap)
+
+	if genHeap.Len() != 3 {
+		t.Errorf("expected length to be 3, got %d", genHeap.Len())
+	}
+
+	for _, i := range []int{1, 2, 3} {
+		v := heap.Pop(&genHeap).(val)
+		if v.v != i {
+			t.Errorf("expected %d, got %d", i, v.v)
+		}
+	}
+}
+
+func TestGenericHeapPushPop(t *testing.T) {
+	genHeap := genericHeap[val]{} // empty heap
+	heap.Push(&genHeap, val{v: 3})
+	heap.Push(&genHeap, val{v: 2})
+	heap.Push(&genHeap, val{v: 1})
+
+	if genHeap.Len() != 3 {
+		t.Errorf("expected length to be 3, got %d", genHeap.Len())
+	}
+
+	for _, i := range []int{1, 2, 3} {
+		v := heap.Pop(&genHeap).(val)
+		if v.v != i {
+			t.Errorf("expected %d, got %d", i, v.v)
+		}
+	}
+}

internal/queue/timepriorityqueue.go

@@ -0,0 +1,78 @@
+package queue
+
+import (
+	"container/heap"
+	"context"
+	"sync"
+	"time"
+)
+
+// TimePriorityQueue is a priority queue that dequeues elements at (or after) a specified time, and prioritizes elements based on a priority value. It is safe for concurrent use.
+type TimePriorityQueue[T any] struct {
+	mu     sync.Mutex
+	tqueue TimeQueue[priorityEntry[T]]
+	ready  genericHeap[priorityEntry[T]]
+}
+
+func NewTimePriorityQueue[T any]() *TimePriorityQueue[T] {
+	return &TimePriorityQueue[T]{
+		tqueue: TimeQueue[priorityEntry[T]]{},
+		ready:  genericHeap[priorityEntry[T]]{},
+	}
+}
+
+func (t *TimePriorityQueue[T]) Len() int {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return t.tqueue.Len() + t.ready.Len()
+}
+
+func (t *TimePriorityQueue[T]) Peek() T {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.ready.Len() > 0 {
+		return t.ready.Peek().v
+	}
+	return t.tqueue.Peek().v
+}
+
+func (t *TimePriorityQueue[T]) Enqueue(at time.Time, priority int, v T) {
+	t.mu.Lock()
+	t.tqueue.Enqueue(at, priorityEntry[T]{at, priority, v})
+	t.mu.Unlock()
+}
+
+func (t *TimePriorityQueue[T]) Dequeue(ctx context.Context) T {
+	t.mu.Lock()
+	for {
+		for t.tqueue.Len() > 0 {
+			thead := t.tqueue.Peek() // peek at the head of the time queue
+			if thead.at.Before(time.Now()) {
+				tqe := heap.Pop(&t.tqueue.heap).(timeQueueEntry[priorityEntry[T]])
+				heap.Push(&t.ready, tqe.v)
+			} else {
+				break
+			}
+		}
+		if t.ready.Len() > 0 {
+			defer t.mu.Unlock()
+			return heap.Pop(&t.ready).(priorityEntry[T]).v
+		}
+		t.mu.Unlock()
+		// wait for the next element to be ready
+		val := t.tqueue.Dequeue(ctx)
+		t.mu.Lock()
+		heap.Push(&t.ready, val)
+	}
+}
+
+type priorityEntry[T any] struct {
+	at       time.Time
+	priority int
+	v        T
+}
+
+func (t priorityEntry[T]) Less(other priorityEntry[T]) bool {
+	return t.priority > other.priority
+}

internal/queue/timepriorityqueue_test.go

@@ -0,0 +1,53 @@
+package queue
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+// TestTPQEnqueue tests that enqueued elements are retruned highest priority first.
+func TestTPQPriority(t *testing.T) {
+	tpq := NewTimePriorityQueue[int]()
+
+	now := time.Now().Add(-time.Second)
+	for i := 0; i < 100; i++ {
+		tpq.Enqueue(now, i, i)
+	}
+
+	if tpq.Len() != 100 {
+		t.Errorf("expected length to be 100, got %d", tpq.Len())
+	}
+
+	for i := 99; i >= 0; i-- {
+		v := tpq.Dequeue(context.Background())
+		if v != i {
+			t.Errorf("expected %d, got %d", i, v)
+		}
+	}
+}
+
+func TestTPQMixedReadinessStates(t *testing.T) {
+	tpq := NewTimePriorityQueue[int]()
+
+	now := time.Now()
+	for i := 0; i < 100; i++ {
+		tpq.Enqueue(now.Add(-100*time.Millisecond), i, i)
+	}
+	for i := 0; i < 100; i++ {
+		tpq.Enqueue(now.Add(100*time.Millisecond), i, i)
+	}
+
+	if tpq.Len() != 200 {
+		t.Errorf("expected length to be 100, got %d", tpq.Len())
+	}
+
+	for j := 0; j < 2; j++ {
+		for i := 99; i >= 0; i-- {
+			v := tpq.Dequeue(context.Background())
+			if v != i {
+				t.Errorf("pass %d expected %d, got %d", j, i, v)
+			}
+		}
+	}
+}

internal/queue/timequeue.go

@@ -0,0 +1,119 @@
+package queue
+
+import (
+	"container/heap"
+	"context"
+	"sync"
+	"time"
+)
+
+// TimeQueue is a priority queue that dequeues elements at (or after) a specified time. It is safe for concurrent use.
+type TimeQueue[T any] struct {
+	heap genericHeap[timeQueueEntry[T]]
+
+	dequeueMu sync.Mutex
+	mu        sync.Mutex
+	notify    chan struct{}
+}
+
+func NewTimeQueue[T any]() *TimeQueue[T] {
+	return &TimeQueue[T]{
+		heap: genericHeap[timeQueueEntry[T]]{},
+	}
+}
+
+func (t *TimeQueue[T]) Enqueue(at time.Time, v T) {
+	t.mu.Lock()
+	heap.Push(&t.heap, timeQueueEntry[T]{at, v})
+	if t.notify != nil {
+		t.notify <- struct{}{}
+	}
+	t.mu.Unlock()
+}
+
+func (t *TimeQueue[T]) Len() int {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return t.heap.Len()
+}
+
+func (t *TimeQueue[T]) Peek() T {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.heap.Len() == 0 {
+		var zero T
+		return zero
+	}
+	return t.heap.Peek().v
+}
+
+func (t *TimeQueue[T]) Dequeue(ctx context.Context) T {
+	t.dequeueMu.Lock()
+	defer t.dequeueMu.Unlock()
+
+	t.mu.Lock()
+	t.notify = make(chan struct{}, 1)
+	defer func() {
+		t.mu.Lock()
+		close(t.notify)
+		t.notify = nil
+		t.mu.Unlock()
+	}()
+	t.mu.Unlock()
+
+	for {
+		t.mu.Lock()
+
+		var wait time.Duration
+		if t.heap.Len() == 0 {
+			wait = 3 * time.Minute
+		} else {
+			val := t.heap.Peek()
+			wait = time.Until(val.at)
+			if wait <= 0 {
+				t.mu.Unlock()
+				return heap.Pop(&t.heap).(timeQueueEntry[T]).v
+			}
+		}
+		t.mu.Unlock()
+
+		timer := time.NewTimer(wait)
+
+		select {
+		case <-timer.C:
+			t.mu.Lock()
+			val, ok := heap.Pop(&t.heap).(timeQueueEntry[T])
+			if !ok || val.at.After(time.Now()) {
+				t.mu.Unlock()
+				continue
+			}
+			t.mu.Unlock()
+			return val.v
+		case <-t.notify: // new task was added, loop again to ensure we have the earliest task.
+			if !timer.Stop() {
+				<-timer.C
+			}
+			continue
+		case <-ctx.Done():
+			if !timer.Stop() {
+				<-timer.C
+			}
+			var zero T
+			return zero
+		}
+	}
+}
+
+type timeQueueEntry[T any] struct {
+	at time.Time
+	v  T
+}
+
+func (t timeQueueEntry[T]) Less(other timeQueueEntry[T]) bool {
+	return t.at.Before(other.at)
+}
+
+func (t timeQueueEntry[T]) Eq(other timeQueueEntry[T]) bool {
+	return t.at.Equal(other.at)
+}