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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"http"
"log"
"time"
)
const (
numPollers = 2 // number of Poller goroutines to launch
second = 1e9 // one second is 1e9 nanoseconds
pollInterval = 60 * second // how often to poll each URL
statusInterval = 10 * second // how often to log status to stdout
errTimeout = 10 * second // back-off timeout on error
)
var urls = []string{
"http://www.google.com/",
"http://golang.org/",
"http://blog.golang.org/",
}
// State represents the last-known state of a URL.
type State struct {
url string
status string
}
// StateMonitor maintains a map that stores the state of the URLs being
// polled, and prints the current state every updateInterval nanoseconds.
// It returns a chan State to which resource state should be sent.
func StateMonitor(updateInterval int64) chan<- State {
updates := make(chan State)
urlStatus := make(map[string]string)
ticker := time.NewTicker(updateInterval)
go func() {
for {
select {
case <-ticker.C:
logState(urlStatus)
case s := <-updates:
urlStatus[s.url] = s.status
}
}
}()
return updates
}
// logState prints a state map.
func logState(s map[string]string) {
log.Println("Current state:")
for k, v := range s {
log.Printf(" %s %s", k, v)
}
}
// Resource represents an HTTP URL to be polled by this program.
type Resource struct {
url string
errCount int64
}
// Poll executes an HTTP HEAD request for url
// and returns the HTTP status string or an error string.
func (r *Resource) Poll() string {
resp, err := http.Head(r.url)
if err != nil {
log.Println("Error", r.url, err)
r.errCount++
return err.String()
}
r.errCount = 0
return resp.Status
}
// Sleep sleeps for an appropriate interval (dependant on error state)
// before sending the Resource to done.
func (r *Resource) Sleep(done chan *Resource) {
time.Sleep(pollInterval + errTimeout*r.errCount)
done <- r
}
func Poller(in <-chan *Resource, out chan<- *Resource, status chan<- State) {
for r := range in {
s := r.Poll()
status <- State{r.url, s}
out <- r
}
}
func main() {
// create our input and output channels
pending, complete := make(chan *Resource), make(chan *Resource)
// launch the StateMonitor
status := StateMonitor(statusInterval)
// launch some Poller goroutines
for i := 0; i < numPollers; i++ {
go Poller(pending, complete, status)
}
// send some Resources to the pending queue
go func() {
for _, url := range urls {
pending <- &Resource{url: url}
}
}()
for r := range complete {
go r.Sleep(pending)
}
}
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