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)
+}

internal/queue/timequeue_test.go

@@ -0,0 +1,87 @@
+package queue
+
+import (
+	"context"
+	"math/rand"
+	"slices"
+	"testing"
+	"time"
+)
+
+func TestTimeQueue(t *testing.T) {
+	t.Parallel()
+	tqueue := NewTimeQueue[val]()
+
+	for i := 0; i < 100; i++ {
+		tqueue.Enqueue(time.Now().Add(time.Millisecond*time.Duration(i*10)), val{v: i})
+	}
+
+	for i := 0; i < 100; i++ {
+		v := tqueue.Dequeue(context.Background())
+		if v.v != i {
+			t.Errorf("expected %d, got %d", i, v.v)
+		}
+	}
+}
+
+func TestFuzzTimeQueue(t *testing.T) {
+	t.Parallel()
+
+	// generate random values and enqueue them
+	values := make([]val, 100)
+	for i := 0; i < 100; i++ {
+		values[i] = val{v: rand.Intn(1000) - 500}
+	}
+
+	tqueue := NewTimeQueue[val]()
+	now := time.Now()
+	for _, v := range values {
+		tqueue.Enqueue(now.Add(time.Millisecond*time.Duration(v.v)), v)
+	}
+
+	slices.SortFunc(values, func(i, j val) int {
+		if i.v > j.v {
+			return 1
+		}
+		return -1
+	})
+
+	// dequeue the values and check if they are in the correct order
+	for i := 0; i < 100; i++ {
+		v := tqueue.Dequeue(context.Background())
+		if v.v != values[i].v {
+			t.Errorf("expected %d, got %d", values[i].v, v.v)
+		}
+	}
+}
+
+func TestTimeQueueEnqueueWhileWaiting(t *testing.T) {
+	t.Parallel()
+
+	tqueue := NewTimeQueue[val]()
+	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond*500)
+	defer cancel()
+
+	go func() {
+		time.Sleep(time.Millisecond * 50)
+		tqueue.Enqueue(time.Now(), val{v: 1})
+	}()
+
+	v := tqueue.Dequeue(ctx)
+	if v.v != 1 {
+		t.Errorf("expected 1, got %d", v.v)
+	}
+}
+
+func TestTimeQueueDequeueTimeout(t *testing.T) {
+	t.Parallel()
+
+	tqueue := NewTimeQueue[val]()
+	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond*50)
+	defer cancel()
+
+	v := tqueue.Dequeue(ctx)
+	if v.v != 0 {
+		t.Errorf("expected 0, got %d", v.v)
+	}
+}

pkg/restic/io.go

@@ -1,86 +0,0 @@
-package restic
-
-import (
-	"fmt"
-	"io"
-)
-
-// headWriter keeps the first 'limit' bytes in memory.
-type headWriter struct {
-	buf   []byte
-	limit int
-}
-
-var _ io.Writer = &headWriter{}
-
-func (w *headWriter) Write(p []byte) (n int, err error) {
-	if len(w.buf) >= w.limit {
-		return len(p), nil
-	}
-	w.buf = append(w.buf, p...)
-	if len(w.buf) > w.limit {
-		w.buf = w.buf[:w.limit]
-	}
-	return len(p), nil
-}
-
-func (w *headWriter) Bytes() []byte {
-	return w.buf
-}
-
-// tailWriter keeps the last 'limit' bytes in memory.
-type tailWriter struct {
-	buf   []byte
-	limit int
-}
-
-var _ io.Writer = &tailWriter{}
-
-func (w *tailWriter) Write(p []byte) (n int, err error) {
-	w.buf = append(w.buf, p...)
-	if len(w.buf) > w.limit {
-		w.buf = w.buf[len(w.buf)-w.limit:]
-	}
-	return len(p), nil
-}
-
-func (w *tailWriter) Bytes() []byte {
-	return w.buf
-}
-
-type outputCapturer struct {
-	headWriter
-	tailWriter
-	limit      int
-	totalBytes int
-}
-
-var _ io.Writer = &outputCapturer{}
-
-func newOutputCapturer(limit int) *outputCapturer {
-	return &outputCapturer{
-		headWriter: headWriter{limit: limit},
-		tailWriter: tailWriter{limit: limit},
-		limit:      limit,
-	}
-}
-
-func (w *outputCapturer) Write(p []byte) (n int, err error) {
-	w.headWriter.Write(p)
-	w.tailWriter.Write(p)
-	w.totalBytes += len(p)
-	return len(p), nil
-}
-
-func (w *outputCapturer) String() string {
-	head := w.headWriter.Bytes()
-	tail := w.tailWriter.Bytes()
-	if w.totalBytes <= w.limit {
-		return string(head)
-	}
-
-	head = head[:w.limit/2]
-	tail = tail[len(tail)-w.limit/2:]
-
-	return fmt.Sprintf("%s...[%v bytes dropped]...%s", string(head), w.totalBytes-len(head)-len(tail), string(tail))
-}

pkg/restic/io_test.go

@@ -1,24 +0,0 @@
-package restic
-
-import "testing"
-
-func TestOutputCapture(t *testing.T) {
-	c := newOutputCapturer(100)
-
-	c.Write([]byte("hello"))
-
-	if c.String() != "hello" {
-		t.Errorf("expected 'hello', got '%s'", c.String())
-	}
-}
-
-func TestOutputCaptureDrops(t *testing.T) {
-	c := newOutputCapturer(2)
-
-	c.Write([]byte("hello"))
-
-	want := "h...[3 bytes dropped]...o"
-	if c.String() != want {
-		t.Errorf("expected '%s', got '%s'", want, c.String())
-	}
-}