// it is safe for concurrent use by multiple goroutines.
type DurationTracker interface {
	// Track measures time spent in the given function f and
	// aggregates measured duration using aggregateFunction.
	// if Track is invoked with f from multiple goroutines concurrently,
	// then f must be safe to be invoked concurrently by multiple goroutines.
	Track(f func())

// ourselves. After we receive an event for a file descriptor,
// it's our responsibility to ask again to be notified for future
// events for that descriptor. When doing this we must keep track of
// what kind of events the goroutines are currently interested in,
// for example a fd may be open both for reading and writing.
//
// A description of the high level operation of this code
// follows. Networking code will get a file descriptor by some means

)

type Seq2[T1, T2 any] func(yield func(T1, T2) bool)

// ofSliceIndex returns a Seq over the elements of s. It is equivalent
// to range s, except that it splits s into two halves and iterates
// in two separate goroutines.  This is racy if yield is racy, and yield
// will be racy if it contains an early exit.
func ofSliceIndex[T any, S ~[]T](s S) Seq2[int, T] {
	return func(yield func(int, T) bool) {
		c := make(chan bool, 2)

	}
	// Examine the CPU profiler's view. Filter it to only include samples from
	// the single test goroutine. Use labels to execute that filter: they should
	// apply to all work done while that goroutine is getg().m.curg, and they
	// should apply to no other goroutines.
	pprofStacks := make(map[string]int)
	for _, s := range prof.Sample {
		if s.Label["tracing"] != nil {
			var fns []string

  and shouldn't have to maintain their own free pools of connections.
  The 'sql' package should deal with that bookkeeping as needed.  Given
  an *sql.DB, it should be possible to share that instance between
  multiple goroutines, without any extra synchronization.

* Push complexity, where necessary, down into the sql+driver packages,
  rather than exposing it to users. Said otherwise, the sql package

	return func(queue *delayQueue) {
		if queue.enqueue != nil {
			close(queue.enqueue)
		}
		queue.enqueue = make(chan *delayTask, bufferSize)
	}
}

// DelayQueueWorkers sets the number of background worker goroutines await tasks to execute. Effectively the
// maximum number of concurrent tasks.
func DelayQueueWorkers(workers int) DelayQueueOption {
	return func(queue *delayQueue) {
		queue.workers = workers
	}
}

		c[i], err = Dial(ln.Addr().Network(), ln.Addr().String())
		if err != nil {
			t.Fatal(err)
		}
		defer c[i].Close()
	}

	var wg sync.WaitGroup
	wg.Add(goroutines)
	now := time.Now()
	for i := 0; i < goroutines; i++ {
		go func(i int) {
			defer wg.Done()
			// Make the deadlines steadily earlier,
			// to trigger runtime adjusttimers calls.
			for j := tries; j > 0; j-- {

	gss := runningGoroutines()
	if len(gss) == 0 {
		return
	}
	fmt.Fprintf(os.Stderr, "Running goroutines:\n")
	for _, gs := range gss {
		fmt.Fprintf(os.Stderr, "%v\n", gs)
	}
	fmt.Fprintf(os.Stderr, "\n")
}

// runningGoroutines returns a list of remaining goroutines.
func runningGoroutines() []string {
	var gss []string
	b := make([]byte, 2<<20)
	b = b[:runtime.Stack(b, true)]

	c[3] = make(chan int, 3)
	N := int(1e5)
	if testing.Short() {
		N /= 10
	}
	// There are 4 goroutines that send N values on each of the chans,
	// + 4 goroutines that receive N values on each of the chans,
	// + 1 goroutine that sends N values on each of the chans in a single select,
	// + 1 goroutine that receives N values on each of the chans in a single select.

			// all goroutines that already existed at trace begin.
			it.preInit = false
			for gid := range it.createdPreInit {
				// These are goroutines that already existed when tracing started but for which we
				// received neither GoWaiting, GoInSyscall, or GoStart. These are goroutines that are in
				// the states _Gidle or _Grunnable.
				it.extra = append(it.extra, Event{