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