for i := range heap {
		if heap[i].ev.time == 5 {
			heap = heapRemove(heap, i)
			break
		}
	}
	checkHeap(t, heap)
	for i := range heap {
		if heap[i].ev.time == 5 {
			t.Fatalf("failed to remove heap elem with time %d: %s", 5, heapDebugString(heap))
		}
	}

	// Remove tail.
	heap = heapRemove(heap, len(heap)-1)
	checkHeap(t, heap)

}

func heapUpdate(heap []*batchCursor, i int) {
	// Try to sift up.
	if heapSiftUp(heap, i) != i {
		return
	}
	// Try to sift down, if sifting up failed.
	heapSiftDown(heap, i)
}

func heapRemove(heap []*batchCursor, i int) []*batchCursor {
	// Sift index i up to the root, ignoring actual values.
	for i > 0 {
		heap[(i-1)/2], heap[i] = heap[i], heap[(i-1)/2]
		i = (i - 1) / 2
	}

		}
		if ok {
			// If we successfully refreshed, update the heap.
			heapUpdate(r.frontier, i)
		} else {
			// There's nothing else to read. Delete this cursor from the frontier.
			r.frontier = heapRemove(r.frontier, i)
		}
		return true, nil
	}
	// Inject a CPU sample if it comes next.
	if len(r.cpuSamples) != 0 {
		if len(r.frontier) == 0 || r.cpuSamples[0].time < r.frontier[0].ev.time {