func (p *PageChannel) Ref() int64 {
	return atomic.LoadInt64(&p.ref)
}
Ref returns task number
package main
import (
	"encoding/json"
	"html/template"
	"net/url"
	"sync"
	"sync/atomic"
)
type PageChannel struct {
	rec <-chan *HTMLPage
	send chan<- *HTMLPage
	ref int64
	init int64
}
func (p *PageChannel) Add(n int64) {
	if n <= 0 {
		return
	}
	atomic.AddInt64(&p.ref, n)
}
func (p *PageChannel) Del(n int64) {
	if n <= 0 {
		return
	}
	atomic.AddInt64(&p.ref, -n)
}