106 lines
2.3 KiB
Go
106 lines
2.3 KiB
Go
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package main
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import (
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"github.com/rcrowley/goagain"
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"fmt"
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"log"
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"net"
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"sync"
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"syscall"
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"time"
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)
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func init() {
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goagain.Strategy = goagain.Double
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log.SetFlags(log.Lmicroseconds | log.Lshortfile)
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log.SetPrefix(fmt.Sprintf("pid:%d ", syscall.Getpid()))
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}
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func main() {
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// Inherit a net.Listener from our parent process or listen anew.
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ch := make(chan struct{})
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wg := &sync.WaitGroup{}
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wg.Add(1)
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l, err := goagain.Listener()
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if nil != err {
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// Listen on a TCP or a UNIX domain socket (TCP here).
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l, err = net.Listen("tcp", "127.0.0.1:48879")
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if nil != err {
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log.Fatalln(err)
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}
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log.Println("listening on", l.Addr())
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// Accept connections in a new goroutine.
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go serve(l, ch, wg)
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} else {
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// Resume listening and accepting connections in a new goroutine.
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log.Println("resuming listening on", l.Addr())
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go serve(l, ch, wg)
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// If this is the child, send the parent SIGUSR2. If this is the
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// parent, send the child SIGQUIT.
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if err := goagain.Kill(); nil != err {
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log.Fatalln(err)
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}
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}
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// Block the main goroutine awaiting signals.
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sig, err := goagain.Wait(l)
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if nil != err {
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log.Fatalln(err)
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}
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// Do whatever's necessary to ensure a graceful exit like waiting for
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// goroutines to terminate or a channel to become closed.
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//
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// In this case, we'll close the channel to signal the goroutine to stop
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// accepting connections and wait for the goroutine to exit.
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close(ch)
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wg.Wait()
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// If we received SIGUSR2, re-exec the parent process.
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if goagain.SIGUSR2 == sig {
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if err := goagain.Exec(l); nil != err {
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log.Fatalln(err)
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}
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}
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}
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// A very rude server that says hello and then closes your connection.
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func serve(l net.Listener, ch chan struct{}, wg *sync.WaitGroup) {
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defer wg.Done()
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for {
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// Break out of the accept loop on the next iteration after the
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// process was signaled and our channel was closed.
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select {
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case <-ch:
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return
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default:
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}
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// Set a deadline so Accept doesn't block forever, which gives
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// us an opportunity to stop gracefully.
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l.(*net.TCPListener).SetDeadline(time.Now().Add(100e6))
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c, err := l.Accept()
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if nil != err {
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if goagain.IsErrClosing(err) {
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return
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}
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if err.(*net.OpError).Timeout() {
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continue
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}
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log.Fatalln(err)
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}
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c.Write([]byte("Hello, world!\n"))
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c.Close()
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}
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}
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