Properly block on first item.

Makefile

@@ -1,4 +1,4 @@
-btc-crawl: *.go
+btc-crawl: **.go
 	go build .
 
 build: btc-crawl

cmd.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"os"
 	"os/signal"
-	"syscall"
 	"time"
 
 	"github.com/alexcesaro/log"
@@ -25,13 +24,14 @@ var defaultDnsSeeds = []string{
 }
 
 type Options struct {
-	Verbose     []bool        `short:"v" long:"verbose" description:"Show verbose logging."`
-	Output      string        `short:"o" long:"output" description:"File to write result to." default:"btc-crawl.json"`
-	Seed        []string      `short:"s" long:"seed" description:"Override which seeds to use." default-mask:"<bitcoin-core DNS seeds>"`
-	Concurrency int           `short:"c" long:"concurrency" description:"Maximum number of concurrent connections to open." default:"10"`
-	UserAgent   string        `short:"A" long:"user-agent" description:"Client name to advertise while crawling. Should be in format of '/name:x.y.z/'." default:"/btc-crawl:0.1.1/"`
-	PeerAge     time.Duration `long:"peer-age" description:"Ignore discovered peers older than this." default:"24h"`
-	StopAfter   int           `long:"stop-after" description:"Stop crawling after this many results." default:"0"`
+	Verbose        []bool        `short:"v" long:"verbose" description:"Show verbose logging."`
+	Output         string        `short:"o" long:"output" description:"File to write result to." default:"btc-crawl.json"`
+	Seed           []string      `short:"s" long:"seed" description:"Override which seeds to use." default-mask:"<bitcoin-core DNS seeds>"`
+	Concurrency    int           `short:"c" long:"concurrency" description:"Maximum number of concurrent connections to open." default:"10"`
+	ConnectTimeout time.Duration `short:"t" long:"connect-timeout" description:"Maximum time to wait to connect before giving up." default:"10s"`
+	UserAgent      string        `short:"A" long:"user-agent" description:"Client name to advertise while crawling. Should be in format of '/name:x.y.z/'." default:"/btc-crawl:0.1.1/"`
+	PeerAge        time.Duration `long:"peer-age" description:"Ignore discovered peers older than this." default:"24h"`
+	StopAfter      int           `long:"stop-after" description:"Stop crawling after this many results." default:"0"`
 }
 
 var logLevels = []log.Level{
@@ -69,7 +69,9 @@ func main() {
 
 	// Create client and crawler
 	client := NewClient(options.UserAgent)
-	crawler := NewCrawler(client, seedNodes, options.PeerAge)
+	crawler := NewCrawler(client, seedNodes)
+	crawler.PeerAge = options.PeerAge
+	crawler.ConnectTimeout = options.ConnectTimeout
 
 	// Configure output
 	var w *bufio.Writer
@@ -99,7 +101,7 @@ func main() {
 
 	// Construct interrupt handler
 	sig := make(chan os.Signal, 1)
-	signal.Notify(sig, os.Interrupt, syscall.SIGTERM)
+	signal.Notify(sig, os.Interrupt)
 	go func() {
 		<-sig // Wait for ^C signal
 		logger.Warningf("Interrupt signal detected, shutting down gracefully by waiting for active workers to finish.")

crawler.go

@@ -10,15 +10,16 @@ import (
 
 // TODO: Break Client/Peer/Crawler into separate modules.
 type Crawler struct {
-	client       *Client
-	queue        *queue.Queue
-	numSeen      int
-	numUnique    int
-	numConnected int
-	numAttempted int
-	seenFilter   map[string]bool // TODO: Replace with bloom filter?
-	peerAge      time.Duration
-	shutdown     chan struct{}
+	client         *Client
+	queue          *queue.Queue
+	numSeen        int
+	numUnique      int
+	numConnected   int
+	numAttempted   int
+	seenFilter     map[string]bool // TODO: Replace with bloom filter?
+	PeerAge        time.Duration
+	ConnectTimeout time.Duration
+	shutdown       chan struct{}
 }
 
 type Result struct {
@@ -26,11 +27,10 @@ type Result struct {
 	Peers []*btcwire.NetAddress
 }
 
-func NewCrawler(client *Client, seeds []string, peerAge time.Duration) *Crawler {
+func NewCrawler(client *Client, seeds []string) *Crawler {
 	c := Crawler{
 		client:     client,
 		seenFilter: map[string]bool{},
-		peerAge:    peerAge,
 		shutdown:   make(chan struct{}, 1),
 	}
 	filter := func(address string) *string {
@@ -57,6 +57,7 @@ func (c *Crawler) handleAddress(address string) *Result {
 
 	client := c.client
 	peer := NewPeer(client, address)
+	peer.ConnectTimeout = c.ConnectTimeout
 	r := Result{Node: peer}
 
 	err := peer.Connect()
@@ -131,7 +132,7 @@ func (c *Crawler) filter(address string) *string {
 }
 
 func (c *Crawler) process(r *Result) *Result {
-	timestampSince := time.Now().Add(-c.peerAge)
+	timestampSince := time.Now().Add(-c.PeerAge)
 
 	for _, addr := range r.Peers {
 		if !addr.Timestamp.After(timestampSince) {
@@ -155,6 +156,9 @@ func (c *Crawler) Run(resultChan chan<- Result, numWorkers int) {
 	numActive := 0
 	isActive := true
 
+	// Block until we get the first item
+	c.queue.Wait()
+
 	// This is the main "event loop".
 	// FIXME: Feels like there should be a better way to manage the number of
 	// concurrent workers without limiting slots with workerChan and without
@@ -165,6 +169,14 @@ func (c *Crawler) Run(resultChan chan<- Result, numWorkers int) {
 			if !isActive {
 				// Don't start any new workers, leave the slot filled.
 				break
+			} else if c.queue.IsEmpty() {
+				<-workerChan
+
+				if numActive == 0 {
+					logger.Infof("Done.")
+					close(resultChan)
+					return
+				}
 			}
 
 			numActive++
@@ -178,13 +190,7 @@ func (c *Crawler) Run(resultChan chan<- Result, numWorkers int) {
 			if c.process(&r) != nil {
 				resultChan <- r
 			}
-
 			numActive--
-			if (!isActive || c.queue.IsEmpty()) && numActive == 0 {
-				logger.Infof("Done.")
-				close(resultChan)
-			}
-
 			<-workerChan
 
 		case <-c.shutdown:

peer.go

@@ -3,6 +3,7 @@ package main
 import (
 	"fmt"
 	"net"
+	"time"
 
 	"github.com/conformal/btcwire"
 )
@@ -15,13 +16,15 @@ type Peer struct {
 	Address         string
 	UserAgent       string
 	ProtocolVersion int32
+	ConnectTimeout  time.Duration // For the connect phase (can be overridden)
 }
 
 func NewPeer(client *Client, address string) *Peer {
 	p := Peer{
-		client:  client,
-		pver:    client.pver,
-		Address: address,
+		client:         client,
+		pver:           client.pver,
+		Address:        address,
+		ConnectTimeout: time.Duration(20 * time.Second),
 	}
 	return &p
 }
@@ -30,7 +33,7 @@ func (p *Peer) Connect() error {
 	if p.conn != nil {
 		return fmt.Errorf("Peer already connected, can't connect again.")
 	}
-	conn, err := net.Dial("tcp", p.Address)
+	conn, err := net.DialTimeout("tcp", p.Address, p.ConnectTimeout)
 	if err != nil {
 		return err
 	}

queue/queue.go

@@ -61,5 +61,29 @@ func (q *Queue) next() string {
 }
 
 func (q *Queue) IsEmpty() bool {
-	return len(q.overflow) == 0
+	// FIXME: This effectively cycles the order of the output buffer. Kinda sad.
+
+	if len(q.overflow) > 0 {
+		return true
+	}
+
+	select {
+	case r := <-q.Output:
+		go func() {
+			// Put it back
+			q.Output <- r
+		}()
+		return true
+	default:
+		return false
+	}
+}
+
+func (q *Queue) Wait() {
+	// Wait until there is an Output. Useful for blocking until the queue is
+	// ramped up.
+	r := <-q.Output
+	go func() {
+		q.Output <- r
+	}()
 }