lbcd/signal.go

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// Copyright (c) 2013-2014 Conformal Systems LLC.
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// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package main
import (
"os"
"os/signal"
)
// interruptChannel is used to receive SIGINT (Ctrl+C) signals.
var interruptChannel chan os.Signal
// addHandlerChannel is used to add an interrupt handler to the list of handlers
// to be invoked on SIGINT (Ctrl+C) signals.
var addHandlerChannel = make(chan func())
// mainInterruptHandler listens for SIGINT (Ctrl+C) signals on the
// interruptChannel and invokes the registered interruptCallbacks accordingly.
// It also listens for callback registration. It must be run as a goroutine.
func mainInterruptHandler() {
// interruptCallbacks is a list of callbacks to invoke when a
// SIGINT (Ctrl+C) is received.
var interruptCallbacks []func()
// 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
for {
select {
case <-interruptChannel:
// Ignore more than one shutdown signal.
if isShutdown {
btcdLog.Infof("Received SIGINT (Ctrl+C). " +
"Already shutting down...")
continue
}
isShutdown = true
btcdLog.Infof("Received SIGINT (Ctrl+C). Shutting down...")
// Run handlers in LIFO order.
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for i := range interruptCallbacks {
idx := len(interruptCallbacks) - 1 - i
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callback := interruptCallbacks[idx]
callback()
}
// Signal the main goroutine to shutdown.
go func() {
shutdownChannel <- struct{}{}
}()
case handler := <-addHandlerChannel:
// The shutdown signal has already been received, so
// just invoke and new handlers immediately.
if isShutdown {
handler()
}
interruptCallbacks = append(interruptCallbacks, handler)
}
}
}
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// addInterruptHandler adds a handler to call when a SIGINT (Ctrl+C) is
// received.
func addInterruptHandler(handler func()) {
// Create the channel and start the main interrupt handler which invokes
// all other callbacks and exits if not already done.
if interruptChannel == nil {
interruptChannel = make(chan os.Signal, 1)
signal.Notify(interruptChannel, os.Interrupt)
go mainInterruptHandler()
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}
addHandlerChannel <- handler
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}