func chansend(channel, msg):
  // non-blocking send
  if ready(channel):
    send(channel, msg)
    return

  t0 = now()
  // let scheduler run another goroutine
  // until the channel is ready
  wait_ready(channel)
  duration = now() - t0
  send(channel, msg)
  // sample a fraction of blocking events
  if random_sample(duration):
    s = stacktrace()
    profile[s].count++
    profile[s].duration += duration