From 7f554bd6d6e2d44f8b99d0d4ce53a16f3359ab92 Mon Sep 17 00:00:00 2001
From: Julian K <jk+github@digineo.de>
Date: Wed, 14 Jun 2017 09:44:15 +0200
Subject: [PATCH] [TASK] Delay startup until a multiple of the period since
 zero time (#68)

---
 cmd/yanic/main.go   | 21 +++++++++++++++------
 config_example.toml |  2 ++
 runtime/config.go   |  1 +
 3 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/cmd/yanic/main.go b/cmd/yanic/main.go
index ed23888..115cb48 100644
--- a/cmd/yanic/main.go
+++ b/cmd/yanic/main.go
@@ -6,6 +6,7 @@ import (
 	"os"
 	"os/signal"
 	"syscall"
+	"time"
 
 	"github.com/FreifunkBremen/yanic/database"
 	"github.com/FreifunkBremen/yanic/database/all"
@@ -58,18 +59,26 @@ func main() {
 	nodes.Start()
 	meshviewer.Start(config, nodes)
 
-	if config.Respondd.Enable {
-		collector = respond.NewCollector(connections, nodes, config.Respondd.Interface, config.Respondd.Port)
-		collector.Start(config.Respondd.CollectInterval.Duration)
-		defer collector.Close()
-	}
-
 	if config.Webserver.Enable {
 		log.Println("starting webserver on", config.Webserver.Bind)
 		srv := webserver.New(config.Webserver.Bind, config.Webserver.Webroot)
 		go srv.Close()
 	}
 
+	if config.Respondd.Enable {
+		// Delaying startup to start at a multiple of `duration` since the zero time.
+		if duration := config.Respondd.Synchronize.Duration; duration > 0 {
+			now := time.Now()
+			delay := duration - now.Sub(now.Truncate(duration))
+			log.Printf("delaying %0.1f seconds", delay.Seconds())
+			time.Sleep(delay)
+		}
+
+		collector = respond.NewCollector(connections, nodes, config.Respondd.Interface, config.Respondd.Port)
+		collector.Start(config.Respondd.CollectInterval.Duration)
+		defer collector.Close()
+	}
+
 	// Wait for INT/TERM
 	sigs := make(chan os.Signal, 1)
 	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
diff --git a/config_example.toml b/config_example.toml
index c6e15ba..34ebcf7 100644
--- a/config_example.toml
+++ b/config_example.toml
@@ -1,6 +1,8 @@
 # Send respondd request to update information
 [respondd]
 enable           = true
+# Delay startup until a multiple of the period since zero time
+synchronize      = "1m"
 # how oftern request per multicast
 collect_interval = "1m"
 # on which interface
diff --git a/runtime/config.go b/runtime/config.go
index c5fb4a7..b6b3846 100644
--- a/runtime/config.go
+++ b/runtime/config.go
@@ -10,6 +10,7 @@ import (
 type Config struct {
 	Respondd struct {
 		Enable          bool     `toml:"enable"`
+		Synchronize     Duration `toml:"synchronize"`
 		Interface       string   `toml:"interface"`
 		Port            int      `toml:"port"`
 		CollectInterval Duration `toml:"collect_interval"`