lnd.xprv/signal/signal.go

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// Copyright (c) 2013-2017 The btcsuite developers
// Copyright (c) 2015-2016 The Decred developers
// Heavily inspired by https://github.com/btcsuite/btcd/blob/master/signal.go
// Copyright (C) 2015-2017 The Lightning Network Developers
package signal
import (
"errors"
"os"
"os/signal"
"sync/atomic"
"syscall"
)
var (
// interruptChannel is used to receive SIGINT (Ctrl+C) signals.
interruptChannel = make(chan os.Signal, 1)
// shutdownRequestChannel is used to request the daemon to shutdown
// gracefully, similar to when receiving SIGINT.
shutdownRequestChannel = make(chan struct{})
// started indicates whether we have started our main interrupt handler.
// This field should be used atomically.
started int32
// quit is closed when instructing the main interrupt handler to exit.
quit = make(chan struct{})
// shutdownChannel is closed once the main interrupt handler exits.
shutdownChannel = make(chan struct{})
)
// Intercept starts the interception of interrupt signals. Note that this
// function can only be called once.
func Intercept() error {
if !atomic.CompareAndSwapInt32(&started, 0, 1) {
return errors.New("intercept already started")
}
signalsToCatch := []os.Signal{
os.Interrupt,
os.Kill,
syscall.SIGABRT,
syscall.SIGTERM,
syscall.SIGQUIT,
}
signal.Notify(interruptChannel, signalsToCatch...)
go mainInterruptHandler()
return nil
}
// mainInterruptHandler listens for SIGINT (Ctrl+C) signals on the
// interruptChannel and shutdown requests on the shutdownRequestChannel, and
// invokes the registered interruptCallbacks accordingly. It also listens for
// callback registration.
// It must be run as a goroutine.
func mainInterruptHandler() {
// isShutdown is a flag which is used to indicate whether or not
// the shutdown signal has already been received and hence any future
// attempts to add a new interrupt handler should invoke them
// immediately.
var isShutdown bool
// shutdown invokes the registered interrupt handlers, then signals the
// shutdownChannel.
shutdown := func() {
// Ignore more than one shutdown signal.
if isShutdown {
log.Infof("Already shutting down...")
return
}
isShutdown = true
log.Infof("Shutting down...")
// Signal the main interrupt handler to exit, and stop accept
// post-facto requests.
close(quit)
}
for {
select {
case signal := <-interruptChannel:
log.Infof("Received %v", signal)
shutdown()
case <-shutdownRequestChannel:
log.Infof("Received shutdown request.")
shutdown()
case <-quit:
log.Infof("Gracefully shutting down.")
close(shutdownChannel)
return
}
}
}
// Listening returns true if the main interrupt handler has been started, and
// has not been killed.
func Listening() bool {
// If our started field is not set, we are not yet listening for
// interrupts.
if atomic.LoadInt32(&started) != 1 {
return false
}
// If we have started our main goroutine, we check whether we have
// stopped it yet.
return Alive()
}
// Alive returns true if the main interrupt handler has not been killed.
func Alive() bool {
select {
case <-quit:
return false
default:
return true
}
}
// RequestShutdown initiates a graceful shutdown from the application.
func RequestShutdown() {
select {
case shutdownRequestChannel <- struct{}{}:
case <-quit:
}
}
// ShutdownChannel returns the channel that will be closed once the main
// interrupt handler has exited.
func ShutdownChannel() <-chan struct{} {
return shutdownChannel
}