agent.go
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package main import ( "fmt" "log" "sync" "github.com/hashicorp/serf/serf" ) // Agent starts and manages a Serf & adds service discovery (TODO) type Agent struct { serfConf *serf.Config eventCh chan serf.Event // This is the underlying Serf we are wrapping serf *serf.Serf // this channel receiving a signal = shutdown shutdown bool shutdownCh chan struct{} shutdownLock sync.Mutex } func Create(serfConf *serf.Config) *Agent { // Create a channel to listen for events from Serf eventCh := make(chan serf.Event, 64) serfConf.EventCh = eventCh // Setup the agent agent := &Agent{ serfConf: serfConf, eventCh: eventCh, shutdownCh: make(chan struct{}), } return agent } func (a *Agent) eventLoop() { serfShutdownCh := a.serf.ShutdownCh() for { select { case e := <-a.eventCh: log.Printf("[INFO] cascade: Received event: %s", e.String()) case <-serfShutdownCh: log.Printf("[INFO] cascade: serf shutdown detected, quitting eventloop") a.Shutdown() return case <-a.shutdownCh: return } } } func (a *Agent) Start() error { log.Printf("[INFO] cascade: Serf agent starting") // Create serf first serf, err := serf.Create(a.serfConf) if err != nil { return fmt.Errorf("Error creating Serf: %s", err) } a.serf = serf // Start event loop go a.eventLoop() return nil } // Shutdown closes this agent and all of its processes. Should be preceded // by a Leave for a graceful shutdown. func (a *Agent) Shutdown() error { a.shutdownLock.Lock() defer a.shutdownLock.Unlock() if a.shutdown { return nil } if a.serf == nil { goto EXIT } log.Println("[INFO] cascade: requesting serf shutdown") if err := a.serf.Shutdown(); err != nil { return err } EXIT: log.Println("[INFO] cascade: shutdown complete") a.shutdown = true close(a.shutdownCh) return nil } // Join asks the Serf instance to join. See the Serf.Join function. func (a *Agent) Join(addrs []string) (n int, err error) { log.Printf("[INFO] cascade: joining: %v", addrs) // we always ignore old events because cascade don't // care about the past n, err = a.serf.Join(addrs, true) if n > 0 { log.Printf("[INFO] cascade: joined: %d nodes", n) } if err != nil { log.Printf("[WARN] cascade: error joining: %v", err) } return n, err } // Leave prepares for a graceful shutdown of the agent and its processes func (a *Agent) Leave() error { if a.serf == nil { return nil } log.Println("[INFO] cascade: requesting graceful leave from Serf") return a.serf.Leave() } // ShutdownCh returns a channel that can be selected to wait // for the agent to perform a shutdown. func (a *Agent) ShutdownCh() <-chan struct{} { return a.shutdownCh }