}
		defer conn.Close()
		for i := 0; i < 10; i++ {
			fmt.Fprintf(conn, "%d\n", i)
			time.Sleep(time.Millisecond)
		}
	}()

	wg.Wait()
	if v := netpollWaiters.Load(); v != 0 {
		log.Fatalf("current waiters %v", v)
	}

	fmt.Println("OK")

	s.mu.Unlock()
}

func (s *Weighted) notifyWaiters() {
	for {
		next := s.waiters.Front()
		if next == nil {
			break // No more waiters blocked.
		}

		w := next.Value.(waiter)
		if s.size-s.cur < w.n {
			// Not enough tokens for the next waiter.  We could keep going (to try to
			// find a waiter with a smaller request), but under load that could cause

// 1 bit - lock for read operations.
// 1 bit - lock for write operations.
// 20 bits - total number of references (read+write+misc).
// 20 bits - number of outstanding read waiters.
// 20 bits - number of outstanding write waiters.
const (
	mutexClosed  = 1 << 0
	mutexRLock   = 1 << 1
	mutexWLock   = 1 << 2
	mutexRef     = 1 << 3
	mutexRefMask = (1<<20 - 1) << 3
	mutexRWait   = 1 << 23

					s.next.parent = s
				}
				// Add t first in s's wait list.
				s.waitlink = t
				s.waittail = t.waittail
				if s.waittail == nil {
					s.waittail = t
				}
				s.waiters = t.waiters
				if s.waiters+1 != 0 {
					s.waiters++
				}
				t.parent = nil
				t.prev = nil
				t.next = nil
				t.waittail = nil
			} else {
				// Add s to end of t's wait list.
				if t.waittail == nil {

				//
				// Specifically enqueue all the waiters for the first lock,
				// then all the waiters for the second lock.
				//
				// Then, dequeue all the waiters from the first lock, then
				// the second.
				//
				// Each enqueue/dequeue operation should be O(1), because
				// there are exactly 2 locks. This could be O(n) if all
				// the waiters for both locks are on the same list, as it
				// once was.

	// the unlocking goroutine to the waiter at the front of the queue.
	// New arriving goroutines don't try to acquire the mutex even if it appears
	// to be unlocked, and don't try to spin. Instead they queue themselves at
	// the tail of the wait queue.
	//
	// If a waiter receives ownership of the mutex and sees that either
	// (1) it is the last waiter in the queue, or (2) it waited for less than 1 ms,

			// events to run at that or an earlier time.
			// Events should not advance the clock.  But just in case they do...
			now := fec.Now()
			for len(fec.waiters) > 0 && !now.Before(fec.waiters[0].targetTime) {
				ew := heap.Pop(&fec.waiters).(eventWaiter)
				fec.clientWG.Add(1)
				go func(f eventclock.EventFunc, now time.Time) {
					f(now)
					fec.clientWG.Add(-1)
				}(ew.f, now)
				foundSome = true

func TestCondSignalStealing(t *testing.T) {
	for iters := 0; iters < 1000; iters++ {
		var m Mutex
		cond := NewCond(&m)

		// Start a waiter.
		ch := make(chan struct{})
		go func() {
			m.Lock()
			ch <- struct{}{}
			cond.Wait()
			m.Unlock()

			ch <- struct{}{}
		}()

		<-ch
		m.Lock()
		m.Unlock()

		// We know that the waiter is in the cond.Wait() call because we

// Test for select: Issue 2075
// A bug in select corrupts channel queues of failed cases
// if there are multiple waiters on those channels and the
// select is the last in the queue. If further waits are made
// on the channel without draining it first then those waiters
// will never wake up. In the code below c1 is such a channel.

package main

func main() {
	c1 := make(chan bool)
	c2 := make(chan bool)

	}
	// This goroutine has set counter to 0 when waiters > 0.
	// Now there can't be concurrent mutations of state:
	// - Adds must not happen concurrently with Wait,
	// - Wait does not increment waiters if it sees counter == 0.
	// Still do a cheap sanity check to detect WaitGroup misuse.
	if wg.state.Load() != state {
		panic("sync: WaitGroup misuse: Add called concurrently with Wait")
	}
	// Reset waiters count to 0.
	wg.state.Store(0)