New queue.

Makefile

@@ -0,0 +1,10 @@
+btc-crawl: *.go
+	go build .
+
+build: btc-crawl
+
+clean:
+	rm btc-crawl
+
+run: btc-crawl
+	./btc-crawl -v

cmd.go

@@ -29,7 +29,7 @@ type Options struct {
 	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"`
+	StopAfter   int           `long:"stop-after" description:"Stop crawling after this many results." default:"-1"`
 }
 
 var logLevels = []log.Level{

crawler.go

@@ -3,16 +3,21 @@ package main
 import (
 	"time"
 
+	"./queue"
+
 	"github.com/conformal/btcwire"
 )
 
 // TODO: Break Client/Peer/Crawler into separate modules.
 type Crawler struct {
-	client     *Client
+	client       *Client
-	count      int
+	queue        *queue.Queue
-	seenFilter map[string]bool // TODO: Replace with bloom filter?
+	numSeen      int
-	queue      []string
+	numUnique    int
-	peerAge    time.Duration
+	numConnected int
+	numAttempted int
+	seenFilter   map[string]bool // TODO: Replace with bloom filter?
+	peerAge      time.Duration
 }
 
 type Result struct {
@@ -20,24 +25,30 @@ type Result struct {
 	Peers []*btcwire.NetAddress
 }
 
-func NewCrawler(client *Client, queue []string, peerAge time.Duration) *Crawler {
+func NewCrawler(client *Client, seeds []string, peerAge time.Duration) *Crawler {
 	c := Crawler{
 		client:     client,
-		count:      0,
 		seenFilter: map[string]bool{},
-		queue:      []string{},
 		peerAge:    peerAge,
 	}
-
+	filter := func(address string) *string {
-	// Prefill the queue
+		return c.filter(address)
-	for _, address := range queue {
-		c.addAddress(address)
 	}
+	c.queue = queue.NewQueue(filter, 10)
+
+	go func() {
+		// Prefill the queue
+		for _, address := range seeds {
+			c.queue.Input <- address
+		}
+	}()
 
 	return &c
 }
 
 func (c *Crawler) handleAddress(address string) *Result {
+	c.numAttempted++
+
 	client := c.client
 	peer := NewPeer(client, address)
 	r := Result{Node: peer}
@@ -62,6 +73,8 @@ func (c *Crawler) handleAddress(address string) *Result {
 		return &r
 	}
 
+	c.numConnected++
+
 	// Listen for tx inv messages.
 	firstReceived := -1
 	tolerateMessages := 3
@@ -97,23 +110,69 @@ func (c *Crawler) handleAddress(address string) *Result {
 	}
 }
 
-func (c *Crawler) addAddress(address string) bool {
+func (c *Crawler) filter(address string) *string {
 	// Returns true if not seen before, otherwise false
+	c.numSeen++
+
 	state, ok := c.seenFilter[address]
 	if ok == true && state == true {
-		return false
+		return nil
 	}
 
 	c.seenFilter[address] = true
-	c.count += 1
+	c.numUnique++
-	c.queue = append(c.queue, address)
+	return &address
-
-	return true
 }
 
+/*
+func (c *Crawler) Run(resultChan chan<- Result, numWorkers int) {
+	workChan := make(chan string, numWorkers)
+	queueChan := make(chan string)
+	tempResult := make(chan Result)
+
+	go func(queueChan <-chan string) {
+		// Single thread to safely manage the queue
+		c.addAddress(<-queueChan)
+		nextAddress, _ := c.popAddress()
+
+		for {
+			select {
+			case address := <-queueChan:
+				// Enque address
+				c.addAddress(address)
+			case workChan <- nextAddress:
+				nextAddress, err := c.popAddress()
+				if err != nil {
+					// Block until we get more work
+					c.addAddress(<-queueChan)
+					nextAddress, _ = c.popAddress()
+				}
+			}
+		}
+	}(queueChan)
+
+	go func(tempResult <-chan Result, workChan chan<- string) {
+		// Convert from result to queue.
+		for {
+			select {
+			case r := <-tempResult:
+
+			}
+		}
+	}(tempResult, workChan)
+
+	for address := range workChan {
+		// Spawn more workers as we get buffered work
+		go func() {
+			logger.Debugf("[%s] Worker started.", address)
+			tempResult <- *c.handleAddress(address)
+		}()
+	}
+}
+*/
+
 func (c *Crawler) Run(numWorkers int, stopAfter int) *[]Result {
 	numActive := 0
-	numGood := 0
 
 	resultChan := make(chan Result)
 	workerChan := make(chan struct{}, numWorkers)
@@ -130,24 +189,13 @@ func (c *Crawler) Run(numWorkers int, stopAfter int) *[]Result {
 	for {
 		select {
 		case workerChan <- struct{}{}:
-			if len(c.queue) == 0 {
-				// No work yet.
-				<-workerChan
-				continue
-			}
-
-			// Pop from the queue
-			address := c.queue[0]
-			c.queue = c.queue[1:]
-			numActive += 1
-
 			go func() {
+				address := <-c.queue.Output
 				logger.Debugf("[%s] Worker started.", address)
 				resultChan <- *c.handleAddress(address)
 			}()
 
 		case r := <-resultChan:
-			newAdded := 0
 			timestampSince := time.Now().Add(-c.peerAge)
 
 			for _, addr := range r.Peers {
@@ -155,24 +203,19 @@ func (c *Crawler) Run(numWorkers int, stopAfter int) *[]Result {
 					continue
 				}
 
-				if c.addAddress(NetAddressKey(addr)) {
+				c.queue.Input <- NetAddressKey(addr)
-					newAdded += 1
-				}
 			}
 
-			if newAdded > 0 {
+			numActive--
-				numGood += 1
-			}
-			numActive -= 1
 
 			if len(r.Peers) > 0 {
 				stopAfter--
 				results = append(results, r)
 
-				logger.Infof("Added %d new peers of %d returned. Total %d known peers via %d connected.", newAdded, len(r.Peers), c.count, numGood)
+				logger.Infof("[%s] Returned %d peers. Total %d unique peers via %d connected (of %d attempted).", r.Node.Address, len(r.Peers), c.numUnique, c.numConnected, c.numAttempted)
 			}
 
-			if stopAfter == 0 || (len(c.queue) == 0 && numActive == 0) {
+			if stopAfter == 0 || (c.queue.IsEmpty() && numActive == 0) {
 				logger.Infof("Done.")
 				return &results
 			}

queue/queue.go

@@ -0,0 +1,65 @@
+package queue
+
+// A single goroutine manages the overflow queue for thread-safety, funneling
+// data between the Input and Output channels through a specified filter.
+type Queue struct {
+	Input    chan string
+	Output   chan string
+	overflow []string
+	filter   func(string) *string
+}
+
+func NewQueue(filter func(string) *string, bufferSize int) *Queue {
+	q := Queue{
+		Input:    make(chan string, bufferSize),
+		Output:   make(chan string, bufferSize),
+		overflow: []string{},
+		filter:   filter,
+	}
+
+	go func(input <-chan string, output chan<- string) {
+		// Block until we have a next item
+		nextItem := q.next()
+
+		for {
+			select {
+			case input := <-q.Input:
+				// New input
+				r := q.filter(input)
+				if r != nil {
+					// Store in the overflow
+					q.overflow = append(q.overflow, *r)
+				}
+			case output <- nextItem:
+				// Block until we have more inputs
+				nextItem = q.next()
+			}
+		}
+	}(q.Input, q.Output)
+
+	return &q
+}
+
+func (q *Queue) next() string {
+	// Block until a next item is available.
+
+	if len(q.overflow) > 0 {
+		// Pop off the overflow queue.
+		r := q.overflow[0]
+		q.overflow = q.overflow[1:]
+		return r
+	}
+
+	for {
+		// Block until we have a viable output
+		r := q.filter(<-q.Input)
+
+		if r != nil {
+			return *r
+		}
+	}
+}
+
+func (q *Queue) IsEmpty() bool {
+	return len(q.overflow) == 0
+}