swarm/storage: fix chunker when reader is broken

* brokenLimitedReader gives error after half size
* TestRandomBrokenData tests chunker with broken reader
* add blocking quitC (instead of errC) and use errC only for errors
* don't close chunkC in tester Split,
* use quitC to quit chunk storage loop
This commit is contained in:
aron 2016-10-08 12:33:52 +02:00
parent be6a3696a9
commit a45421baaf
4 changed files with 89 additions and 101 deletions

View File

@ -23,8 +23,6 @@ import (
"hash"
"io"
"sync"
// "github.com/ethereum/go-ethereum/logger"
// "github.com/ethereum/go-ethereum/logger/glog"
)
/*
@ -124,12 +122,13 @@ func (self *TreeChunker) Split(data io.Reader, size int64, chunkC chan *Chunk, s
jobC := make(chan *hashJob, 2*processors)
wg := &sync.WaitGroup{}
errC := make(chan error)
quitC := make(chan bool)
// wwg = workers waitgroup keeps track of hashworkers spawned by this split call
if wwg != nil {
wwg.Add(1)
}
go self.hashWorker(jobC, chunkC, errC, swg, wwg)
go self.hashWorker(jobC, chunkC, errC, quitC, swg, wwg)
depth := 0
treeSize := self.chunkSize
@ -141,11 +140,10 @@ func (self *TreeChunker) Split(data io.Reader, size int64, chunkC chan *Chunk, s
}
key := make([]byte, self.hashFunc().Size())
// glog.V(logger.Detail).Infof("split request received for data (%v bytes, depth: %v)", size, depth)
// this waitgroup member is released after the root hash is calculated
wg.Add(1)
//launch actual recursive function passing the waitgroups
go self.split(depth, treeSize/self.branches, key, data, size, jobC, chunkC, errC, wg, swg, wwg)
go self.split(depth, treeSize/self.branches, key, data, size, jobC, chunkC, errC, quitC, wg, swg, wwg)
// closes internal error channel if all subprocesses in the workgroup finished
go func() {
@ -153,7 +151,6 @@ func (self *TreeChunker) Split(data io.Reader, size int64, chunkC chan *Chunk, s
wg.Wait()
// if storage waitgroup is non-nil, we wait for storage to finish too
if swg != nil {
// glog.V(logger.Detail).Infof("Waiting for storage to finish")
swg.Wait()
}
close(errC)
@ -162,14 +159,15 @@ func (self *TreeChunker) Split(data io.Reader, size int64, chunkC chan *Chunk, s
select {
case err := <-errC:
if err != nil {
close(quitC)
return nil, err
}
//
//TODO: add a timeout
}
return key, nil
}
func (self *TreeChunker) split(depth int, treeSize int64, key Key, data io.Reader, size int64, jobC chan *hashJob, chunkC chan *Chunk, errC chan error, parentWg, swg, wwg *sync.WaitGroup) {
func (self *TreeChunker) split(depth int, treeSize int64, key Key, data io.Reader, size int64, jobC chan *hashJob, chunkC chan *Chunk, errC chan error, quitC chan bool, parentWg, swg, wwg *sync.WaitGroup) {
for depth > 0 && size < treeSize {
treeSize /= self.branches
@ -180,17 +178,20 @@ func (self *TreeChunker) split(depth int, treeSize int64, key Key, data io.Reade
// leaf nodes -> content chunks
chunkData := make([]byte, size+8)
binary.LittleEndian.PutUint64(chunkData[0:8], uint64(size))
data.Read(chunkData[8:])
select {
case jobC <- &hashJob{key, chunkData, size, parentWg}:
case <-errC:
}
// glog.V(logger.Detail).Infof("read %v", size)
_, err := data.Read(chunkData[8:])
if err != nil {
errC <- err
return
}
select {
case jobC <- &hashJob{key, chunkData, size, parentWg}:
case <-quitC:
}
return
}
// dept > 0
// intermediate chunk containing child nodes hashes
branchCnt := int64((size + treeSize - 1) / treeSize)
// glog.V(logger.Detail).Infof("intermediate node: setting branches: %v, depth: %v, max subtree size: %v, data size: %v", branches, depth, treeSize, size)
var chunk []byte = make([]byte, branchCnt*self.hashSize+8)
var pos, i int64
@ -210,7 +211,7 @@ func (self *TreeChunker) split(depth int, treeSize int64, key Key, data io.Reade
subTreeKey := chunk[8+i*self.hashSize : 8+(i+1)*self.hashSize]
childrenWg.Add(1)
self.split(depth-1, treeSize/self.branches, subTreeKey, data, secSize, jobC, chunkC, errC, childrenWg, swg, wwg)
self.split(depth-1, treeSize/self.branches, subTreeKey, data, secSize, jobC, chunkC, errC, quitC, childrenWg, swg, wwg)
i++
pos += treeSize
@ -224,15 +225,15 @@ func (self *TreeChunker) split(depth int, treeSize int64, key Key, data io.Reade
wwg.Add(1)
}
self.workerCount++
go self.hashWorker(jobC, chunkC, errC, swg, wwg)
go self.hashWorker(jobC, chunkC, errC, quitC, swg, wwg)
}
select {
case jobC <- &hashJob{key, chunk, size, parentWg}:
case <-errC:
case <-quitC:
}
}
func (self *TreeChunker) hashWorker(jobC chan *hashJob, chunkC chan *Chunk, errC chan error, swg, wwg *sync.WaitGroup) {
func (self *TreeChunker) hashWorker(jobC chan *hashJob, chunkC chan *Chunk, errC chan error, quitC chan bool, swg, wwg *sync.WaitGroup) {
hasher := self.hashFunc()
if wwg != nil {
defer wwg.Done()
@ -247,8 +248,7 @@ func (self *TreeChunker) hashWorker(jobC chan *hashJob, chunkC chan *Chunk, errC
// now we got the hashes in the chunk, then hash the chunks
hasher.Reset()
self.hashChunk(hasher, job, chunkC, swg)
// glog.V(logger.Detail).Infof("hash chunk (%v)", job.size)
case <-errC:
case <-quitC:
return
}
}
@ -276,6 +276,7 @@ func (self *TreeChunker) hashChunk(hasher hash.Hash, job *hashJob, chunkC chan *
}
}
job.parentWg.Done()
if chunkC != nil {
chunkC <- newChunk
}
@ -328,7 +329,6 @@ func (self *LazyChunkReader) Size(quitC chan bool) (n int64, err error) {
func (self *LazyChunkReader) ReadAt(b []byte, off int64) (read int, err error) {
// this is correct, a swarm doc cannot be zero length, so no EOF is expected
if len(b) == 0 {
// glog.V(logger.Detail).Infof("Size query for %v", chunk.Key.Log())
return 0, nil
}
quitC := make(chan bool)
@ -336,13 +336,10 @@ func (self *LazyChunkReader) ReadAt(b []byte, off int64) (read int, err error) {
if err != nil {
return 0, err
}
// glog.V(logger.Detail).Infof("readAt: len(b): %v, off: %v, size: %v ", len(b), off, size)
errC := make(chan error)
// glog.V(logger.Detail).Infof("readAt: reading %v into %d bytes at offset %d.", self.chunk.Key.Log(), len(b), off)
// }
// glog.V(logger.Detail).Infof("-> want: %v, off: %v size: %v ", want, off, self.size)
var treeSize int64
var depth int
// calculate depth and max treeSize
@ -364,22 +361,16 @@ func (self *LazyChunkReader) ReadAt(b []byte, off int64) (read int, err error) {
return 0, err
}
// glog.V(logger.Detail).Infof("ReadAt received %v", err)
// glog.V(logger.Detail).Infof("end: len(b): %v, off: %v, size: %v ", len(b), off, size)
if off+int64(len(b)) >= size {
// glog.V(logger.Detail).Infof(" len(b): %v EOF", len(b))
return len(b), io.EOF
}
// glog.V(logger.Detail).Infof("ReadAt returning at %d: %v", read, err)
return len(b), nil
}
func (self *LazyChunkReader) join(b []byte, off int64, eoff int64, depth int, treeSize int64, chunk *Chunk, parentWg *sync.WaitGroup, errC chan error, quitC chan bool) {
defer parentWg.Done()
// return NewDPA(&LocalStore{})
// glog.V(logger.Detail).Infof("inh len(b): %v, off: %v eoff: %v ", len(b), off, eoff)
// glog.V(logger.Detail).Infof("depth: %v, loff: %v, eoff: %v, chunk.Size: %v, treeSize: %v", depth, off, eoff, chunk.Size, treeSize)
// chunk.Size = int64(binary.LittleEndian.Uint64(chunk.SData[0:8]))
@ -391,7 +382,6 @@ func (self *LazyChunkReader) join(b []byte, off int64, eoff int64, depth int, tr
// leaf chunk found
if depth == 0 {
// glog.V(logger.Detail).Infof("depth: %v, len(b): %v, off: %v, eoff: %v, chunk.Size: %v %v, treeSize: %v", depth, len(b), off, eoff, chunk.Size, len(chunk.SData), treeSize)
extra := 8 + eoff - int64(len(chunk.SData))
if extra > 0 {
eoff -= extra
@ -406,7 +396,6 @@ func (self *LazyChunkReader) join(b []byte, off int64, eoff int64, depth int, tr
wg := &sync.WaitGroup{}
defer wg.Wait()
// glog.V(logger.Detail).Infof("start %v,end %v", start, end)
for i := start; i < end; i++ {
soff := i * treeSize
@ -425,7 +414,6 @@ func (self *LazyChunkReader) join(b []byte, off int64, eoff int64, depth int, tr
wg.Add(1)
go func(j int64) {
childKey := chunk.SData[8+j*self.hashSize : 8+(j+1)*self.hashSize]
// glog.V(logger.Detail).Infof("subtree ind.ex: %v -> %v", j, childKey.Log())
chunk := retrieve(childKey, self.chunkC, quitC)
if chunk == nil {
select {
@ -450,7 +438,6 @@ func retrieve(key Key, chunkC chan *Chunk, quitC chan bool) *Chunk {
Key: key,
C: make(chan bool), // close channel to signal data delivery
}
// glog.V(logger.Detail).Infof("chunk data sent for %v (key interval in chunk %v-%v)", ch.Key.Log(), j*self.chunker.hashSize, (j+1)*self.chunker.hashSize)
// submit chunk for retrieval
select {
case chunkC <- chunk: // submit retrieval request, someone should be listening on the other side (or we will time out globally)
@ -464,7 +451,6 @@ func retrieve(key Key, chunkC chan *Chunk, quitC chan bool) *Chunk {
// this is how we control process leakage (quitC is closed once join is finished (after timeout))
return nil
case <-chunk.C: // bells are ringing, data have been delivered
// glog.V(logger.Detail).Infof("chunk data received")
}
if len(chunk.SData) == 0 {
return nil // chunk.Size = int64(binary.LittleEndian.Uint64(chunk.SData[0:8]))
@ -476,7 +462,6 @@ func retrieve(key Key, chunkC chan *Chunk, quitC chan bool) *Chunk {
// Read keeps a cursor so cannot be called simulateously, see ReadAt
func (self *LazyChunkReader) Read(b []byte) (read int, err error) {
read, err = self.ReadAt(b, self.off)
// glog.V(logger.Detail).Infof("read: %v, off: %v, error: %v", read, self.off, err)
self.off += int64(read)
return

View File

@ -18,6 +18,7 @@ package storage
import (
"bytes"
"crypto/rand"
"encoding/binary"
"fmt"
"io"
@ -27,6 +28,7 @@ import (
"time"
)
/*
Tests TreeChunker by splitting and joining a random byte slice
*/
@ -49,7 +51,7 @@ func (self *chunkerTester) checkChunks(t *testing.T, want int) {
}
}
func (self *chunkerTester) Split(chunker Splitter, data io.Reader, size int64, chunkC chan *Chunk, swg *sync.WaitGroup) (key Key) {
func (self *chunkerTester) Split(chunker Splitter, data io.Reader, size int64, chunkC chan *Chunk, swg *sync.WaitGroup, expectedError error) (key Key) {
// reset
self.chunks = make(map[string]*Chunk)
@ -65,14 +67,9 @@ func (self *chunkerTester) Split(chunker Splitter, data io.Reader, size int64, c
select {
case <-timeout:
self.t.Fatalf("Join timeout error")
case chunk, ok := <-chunkC:
if !ok {
// glog.V(logger.Info).Infof("chunkC closed quitting")
close(quitC)
case <-quitC:
return
}
// glog.V(logger.Info).Infof("chunk %v received", len(self.chunks))
case chunk := <-chunkC:
// self.chunks = append(self.chunks, chunk)
self.chunks[chunk.Key.String()] = chunk
if chunk.wg != nil {
@ -83,21 +80,16 @@ func (self *chunkerTester) Split(chunker Splitter, data io.Reader, size int64, c
}()
}
key, err := chunker.Split(data, size, chunkC, swg, nil)
if err != nil {
if err != nil && expectedError == nil {
self.t.Fatalf("Split error: %v", err)
} else if expectedError != nil && (err == nil || err.Error() != expectedError.Error()) {
self.t.Fatalf("Not receiving the correct error! Expected %v, received %v", expectedError, err)
}
if chunkC != nil {
if swg != nil {
// glog.V(logger.Info).Infof("Waiting for storage to finish")
swg.Wait()
// glog.V(logger.Info).Infof("Storage finished")
}
close(chunkC)
}
if chunkC != nil {
// glog.V(logger.Info).Infof("waiting for splitter finished")
<-quitC
// glog.V(logger.Info).Infof("Splitter finished")
close(quitC)
}
return
}
@ -105,11 +97,9 @@ func (self *chunkerTester) Split(chunker Splitter, data io.Reader, size int64, c
func (self *chunkerTester) Join(chunker Chunker, key Key, c int, chunkC chan *Chunk, quitC chan bool) LazySectionReader {
// reset but not the chunks
// glog.V(logger.Info).Infof("Splitter finished")
reader := chunker.Join(key, chunkC)
timeout := time.After(600 * time.Second)
// glog.V(logger.Info).Infof("Splitter finished")
i := 0
go func() {
for {
@ -122,15 +112,12 @@ func (self *chunkerTester) Join(chunker Chunker, key Key, c int, chunkC chan *Ch
close(quitC)
return
}
// glog.V(logger.Info).Infof("chunk %v: %v", i, chunk.Key.String())
// this just mocks the behaviour of a chunk store retrieval
stored, success := self.chunks[chunk.Key.String()]
// glog.V(logger.Info).Infof("chunk %v, success: %v", chunk.Key.String(), success)
if !success {
self.t.Fatalf("not found")
return
}
// glog.V(logger.Info).Infof("chunk %v: %v", i, chunk.Key.String())
chunk.SData = stored.SData
chunk.Size = int64(binary.LittleEndian.Uint64(chunk.SData[0:8]))
close(chunk.C)
@ -141,6 +128,26 @@ func (self *chunkerTester) Join(chunker Chunker, key Key, c int, chunkC chan *Ch
return reader
}
func testRandomBrokenData(splitter Splitter, n int, tester *chunkerTester) {
data := io.LimitReader(rand.Reader, int64(n))
brokendata := brokenLimitReader(data, n, n/2)
buf := make([]byte, n)
_, err := brokendata.Read(buf)
if err == nil || err.Error() != "Broken reader" {
tester.t.Fatalf("Broken reader is not broken, hence broken. Returns: %v", err)
}
data = io.LimitReader(rand.Reader, int64(n))
brokendata = brokenLimitReader(data, n, n/2)
chunkC := make(chan *Chunk, 1000)
swg := &sync.WaitGroup{}
key := tester.Split(splitter, brokendata, int64(n), chunkC, swg, fmt.Errorf("Broken reader"))
tester.t.Logf(" Key = %v\n", key)
}
func testRandomData(splitter Splitter, n int, tester *chunkerTester) {
if tester.inputs == nil {
tester.inputs = make(map[uint64][]byte)
@ -151,13 +158,13 @@ func testRandomData(splitter Splitter, n int, tester *chunkerTester) {
data, input = testDataReaderAndSlice(n)
tester.inputs[uint64(n)] = input
} else {
data = limitReader(bytes.NewReader(input), n)
data = io.LimitReader(bytes.NewReader(input), int64(n))
}
chunkC := make(chan *Chunk, 1000)
swg := &sync.WaitGroup{}
key := tester.Split(splitter, data, int64(n), chunkC, swg)
key := tester.Split(splitter, data, int64(n), chunkC, swg, nil)
tester.t.Logf(" Key = %v\n", key)
chunkC = make(chan *Chunk, 1000)
@ -166,9 +173,7 @@ func testRandomData(splitter Splitter, n int, tester *chunkerTester) {
chunker := NewTreeChunker(NewChunkerParams())
reader := tester.Join(chunker, key, 0, chunkC, quitC)
output := make([]byte, n)
// glog.V(logger.Info).Infof(" Key = %v\n", key)
r, err := reader.Read(output)
// glog.V(logger.Info).Infof(" read = %v %v\n", r, err)
if r != n || err != io.EOF {
tester.t.Fatalf("read error read: %v n = %v err = %v\n", r, n, err)
}
@ -183,7 +188,7 @@ func testRandomData(splitter Splitter, n int, tester *chunkerTester) {
func TestRandomData(t *testing.T) {
// sizes := []int{123456}
sizes := []int{1, 60, 83, 179, 253, 1024, 4095, 4096, 4097, 123456}
sizes := []int{1, 60, 83, 179, 253, 1024, 4095, 4096, 4097, 8191, 8192, 8193, 123456, 2345678}
tester := &chunkerTester{t: t}
chunker := NewTreeChunker(NewChunkerParams())
for _, s := range sizes {
@ -195,6 +200,16 @@ func TestRandomData(t *testing.T) {
}
}
func TestRandomBrokenData(t *testing.T) {
sizes := []int{1, 60, 83, 179, 253, 1024, 4095, 4096, 4097, 8191, 8192, 8193, 123456, 2345678}
tester := &chunkerTester{t: t}
chunker := NewTreeChunker(NewChunkerParams())
for _, s := range sizes {
testRandomBrokenData(chunker, s, tester)
t.Logf("done size: %v", s)
}
}
func readAll(reader LazySectionReader, result []byte) {
size := int64(len(result))
@ -227,7 +242,7 @@ func benchmarkJoin(n int, t *testing.B) {
chunkC := make(chan *Chunk, 1000)
swg := &sync.WaitGroup{}
key := tester.Split(chunker, data, int64(n), chunkC, swg)
key := tester.Split(chunker, data, int64(n), chunkC, swg, nil)
// t.StartTimer()
chunkC = make(chan *Chunk, 1000)
quitC := make(chan bool)
@ -248,8 +263,7 @@ func benchmarkSplitTree(n int, t *testing.B) {
chunker := NewTreeChunker(NewChunkerParams())
tester := &chunkerTester{t: t}
data := testDataReader(n)
// glog.V(logger.Info).Infof("splitting data of length %v", n)
tester.Split(chunker, data, int64(n), nil, nil)
tester.Split(chunker, data, int64(n), nil, nil, nil)
}
stats := new(runtime.MemStats)
runtime.ReadMemStats(stats)
@ -262,8 +276,7 @@ func benchmarkSplitPyramid(n int, t *testing.B) {
splitter := NewPyramidChunker(NewChunkerParams())
tester := &chunkerTester{t: t}
data := testDataReader(n)
// glog.V(logger.Info).Infof("splitting data of length %v", n)
tester.Split(splitter, data, int64(n), nil, nil)
tester.Split(splitter, data, int64(n), nil, nil, nil)
}
stats := new(runtime.MemStats)
runtime.ReadMemStats(stats)

View File

@ -19,6 +19,7 @@ package storage
import (
"bytes"
"crypto/rand"
"fmt"
"io"
"sync"
"testing"
@ -27,32 +28,31 @@ import (
"github.com/ethereum/go-ethereum/logger/glog"
)
type limitedReader struct {
r io.Reader
off int64
size int64
type brokenLimitedReader struct {
lr io.Reader
errAt int
off int
size int
}
func limitReader(r io.Reader, size int) *limitedReader {
return &limitedReader{r, 0, int64(size)}
}
func (self *limitedReader) Read(buf []byte) (int, error) {
limit := int64(len(buf))
left := self.size - self.off
if limit >= left {
limit = left
func brokenLimitReader(data io.Reader, size int, errAt int) *brokenLimitedReader {
return &brokenLimitedReader{
lr: data,
errAt: errAt,
size: size,
}
n, err := self.r.Read(buf[:limit])
if err == nil && limit == left {
err = io.EOF
}
self.off += int64(n)
return n, err
}
func testDataReader(l int) (r io.Reader) {
return limitReader(rand.Reader, l)
return io.LimitReader(rand.Reader, int64(l))
}
func (self *brokenLimitedReader) Read(buf []byte) (int, error) {
if self.off+len(buf) > self.errAt {
return 0, fmt.Errorf("Broken reader")
}
self.off += len(buf)
return self.lr.Read(buf)
}
func testDataReaderAndSlice(l int) (r io.Reader, slice []byte) {
@ -60,7 +60,7 @@ func testDataReaderAndSlice(l int) (r io.Reader, slice []byte) {
if _, err := rand.Read(slice); err != nil {
panic("rand error")
}
r = limitReader(bytes.NewReader(slice), l)
r = io.LimitReader(bytes.NewReader(slice), int64(l))
return
}

View File

@ -81,7 +81,6 @@ func (self *PyramidChunker) Split(data io.Reader, size int64, chunkC chan *Chunk
chunks := (size + self.chunkSize - 1) / self.chunkSize
depth := int(math.Ceil(math.Log(float64(chunks))/math.Log(float64(self.branches)))) + 1
// glog.V(logger.Detail).Infof("chunks: %v, depth: %v", chunks, depth)
results := Tree{
Chunks: chunks,
@ -99,26 +98,24 @@ func (self *PyramidChunker) Split(data io.Reader, size int64, chunkC chan *Chunk
go self.processor(pend, swg, tasks, chunkC, &results)
}
// Feed the chunks into the task pool
read := 0
for index := 0; ; index++ {
buffer := make([]byte, self.chunkSize+8)
n, err := data.Read(buffer[8:])
last := err == io.ErrUnexpectedEOF || err == io.EOF
// glog.V(logger.Detail).Infof("n: %v, index: %v, depth: %v", n, index, depth)
read += n
last := int64(read) == size || err == io.ErrUnexpectedEOF || err == io.EOF
if err != nil && !last {
// glog.V(logger.Info).Infof("error: %v", err)
close(abortC)
break
}
binary.LittleEndian.PutUint64(buffer[:8], uint64(n))
pend.Add(1)
// glog.V(logger.Info).Infof("-> task %v (%v)", index, n)
select {
case tasks <- &Task{Index: int64(index), Size: uint64(n), Data: buffer[:n+8], Last: last}:
case <-abortC:
return nil, err
}
if last {
// glog.V(logger.Info).Infof("last task %v (%v)", index, n)
break
}
}
@ -126,7 +123,6 @@ func (self *PyramidChunker) Split(data io.Reader, size int64, chunkC chan *Chunk
close(tasks)
pend.Wait()
// glog.V(logger.Info).Infof("len: %v", results.Levels[0][0])
key := results.Levels[0][0].Children[0][:]
return key, nil
}
@ -134,12 +130,10 @@ func (self *PyramidChunker) Split(data io.Reader, size int64, chunkC chan *Chunk
func (self *PyramidChunker) processor(pend, swg *sync.WaitGroup, tasks chan *Task, chunkC chan *Chunk, results *Tree) {
defer pend.Done()
// glog.V(logger.Info).Infof("processor started")
// Start processing leaf chunks ad infinitum
hasher := self.hashFunc()
for task := range tasks {
depth, pow := len(results.Levels)-1, self.branches
// glog.V(logger.Info).Infof("task: %v, last: %v", task.Index, task.Last)
size := task.Size
data := task.Data
var node *Node
@ -171,10 +165,8 @@ func (self *PyramidChunker) processor(pend, swg *sync.WaitGroup, tasks chan *Tas
}
node = &Node{pending, 0, make([]common.Hash, pending), last}
results.Levels[depth][task.Index/pow] = node
// glog.V(logger.Info).Infof("create node %v, %v (%v children, all pending)", depth, task.Index/pow, pending)
}
node.Pending--
// glog.V(logger.Info).Infof("pending now: %v", node.Pending)
i := task.Index / (pow / self.branches) % self.branches
if last {
node.Last = true
@ -182,7 +174,6 @@ func (self *PyramidChunker) processor(pend, swg *sync.WaitGroup, tasks chan *Tas
copy(node.Children[i][:], hash)
node.Size += size
left := node.Pending
// glog.V(logger.Info).Infof("left pending now: %v, node size: %v", left, node.Size)
if chunkC != nil {
if swg != nil {
swg.Add(1)
@ -198,7 +189,6 @@ func (self *PyramidChunker) processor(pend, swg *sync.WaitGroup, tasks chan *Tas
results.Lock.Unlock()
// If there's more work to be done, leave for others
// glog.V(logger.Info).Infof("left %v", left)
if left > 0 {
break
}