code: func (e *endpoint) handleSynSegment(ctx *listenContext, s *segment, opts *header.TCPSynOptions) {
  	defer decSynRcvdCount()
  	defer s.decRef()
  
  	n, err := ctx.createEndpointAndPerformHandshake(s, opts)
  	if err != nil {
  		return
  	}
  
  	e.deliverAccepted(n)
  }
docs: // handleSynSegment is called in its own goroutine once the listening endpoint
  // receives a SYN segment. It is responsible for completing the handshake and
  // queueing the new endpoint for acceptance.
  //
  // A limited number of these goroutines are allowed before TCP starts using SYN
  // cookies to accept connections.