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engine.go
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engine.go
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// package decision implements the decision engine for the bitswap service.
package decision
import (
"sync"
"time"
blocks "github.com/ipfs/go-ipfs/blocks"
bstore "github.com/ipfs/go-ipfs/blocks/blockstore"
bsmsg "github.com/ipfs/go-ipfs/exchange/bitswap/message"
wl "github.com/ipfs/go-ipfs/exchange/bitswap/wantlist"
logging "gx/ipfs/QmNQynaz7qfriSUJkiEZUrm2Wen1u3Kj9goZzWtrPyu7XR/go-log"
peer "gx/ipfs/QmRBqJF7hb8ZSpRcMwUt8hNhydWcxGEhtk81HKq6oUwKvs/go-libp2p-peer"
context "gx/ipfs/QmZy2y8t9zQH2a1b8q2ZSLKp17ATuJoCNxxyMFG5qFExpt/go-net/context"
)
// TODO consider taking responsibility for other types of requests. For
// example, there could be a |cancelQueue| for all of the cancellation
// messages that need to go out. There could also be a |wantlistQueue| for
// the local peer's wantlists. Alternatively, these could all be bundled
// into a single, intelligent global queue that efficiently
// batches/combines and takes all of these into consideration.
//
// Right now, messages go onto the network for four reasons:
// 1. an initial `sendwantlist` message to a provider of the first key in a
// request
// 2. a periodic full sweep of `sendwantlist` messages to all providers
// 3. upon receipt of blocks, a `cancel` message to all peers
// 4. draining the priority queue of `blockrequests` from peers
//
// Presently, only `blockrequests` are handled by the decision engine.
// However, there is an opportunity to give it more responsibility! If the
// decision engine is given responsibility for all of the others, it can
// intelligently decide how to combine requests efficiently.
//
// Some examples of what would be possible:
//
// * when sending out the wantlists, include `cancel` requests
// * when handling `blockrequests`, include `sendwantlist` and `cancel` as
// appropriate
// * when handling `cancel`, if we recently received a wanted block from a
// peer, include a partial wantlist that contains a few other high priority
// blocks
//
// In a sense, if we treat the decision engine as a black box, it could do
// whatever it sees fit to produce desired outcomes (get wanted keys
// quickly, maintain good relationships with peers, etc).
var log = logging.Logger("engine")
const (
// outboxChanBuffer must be 0 to prevent stale messages from being sent
outboxChanBuffer = 0
)
// Envelope contains a message for a Peer
type Envelope struct {
// Peer is the intended recipient
Peer peer.ID
// Block is the payload
Block blocks.Block
// A callback to notify the decision queue that the task is complete
Sent func()
}
type Engine struct {
// peerRequestQueue is a priority queue of requests received from peers.
// Requests are popped from the queue, packaged up, and placed in the
// outbox.
peerRequestQueue *prq
// FIXME it's a bit odd for the client and the worker to both share memory
// (both modify the peerRequestQueue) and also to communicate over the
// workSignal channel. consider sending requests over the channel and
// allowing the worker to have exclusive access to the peerRequestQueue. In
// that case, no lock would be required.
workSignal chan struct{}
// outbox contains outgoing messages to peers. This is owned by the
// taskWorker goroutine
outbox chan (<-chan *Envelope)
bs bstore.Blockstore
lock sync.Mutex // protects the fields immediatly below
// ledgerMap lists Ledgers by their Partner key.
ledgerMap map[peer.ID]*ledger
ticker *time.Ticker
}
func NewEngine(ctx context.Context, bs bstore.Blockstore) *Engine {
e := &Engine{
ledgerMap: make(map[peer.ID]*ledger),
bs: bs,
peerRequestQueue: newPRQ(),
outbox: make(chan (<-chan *Envelope), outboxChanBuffer),
workSignal: make(chan struct{}, 1),
ticker: time.NewTicker(time.Millisecond * 100),
}
go e.taskWorker(ctx)
return e
}
func (e *Engine) WantlistForPeer(p peer.ID) (out []wl.Entry) {
e.lock.Lock()
partner, ok := e.ledgerMap[p]
if ok {
out = partner.wantList.SortedEntries()
}
e.lock.Unlock()
return out
}
func (e *Engine) taskWorker(ctx context.Context) {
defer close(e.outbox) // because taskWorker uses the channel exclusively
for {
oneTimeUse := make(chan *Envelope, 1) // buffer to prevent blocking
select {
case <-ctx.Done():
return
case e.outbox <- oneTimeUse:
}
// receiver is ready for an outoing envelope. let's prepare one. first,
// we must acquire a task from the PQ...
envelope, err := e.nextEnvelope(ctx)
if err != nil {
close(oneTimeUse)
return // ctx cancelled
}
oneTimeUse <- envelope // buffered. won't block
close(oneTimeUse)
}
}
// nextEnvelope runs in the taskWorker goroutine. Returns an error if the
// context is cancelled before the next Envelope can be created.
func (e *Engine) nextEnvelope(ctx context.Context) (*Envelope, error) {
for {
nextTask := e.peerRequestQueue.Pop()
for nextTask == nil {
select {
case <-ctx.Done():
return nil, ctx.Err()
case <-e.workSignal:
nextTask = e.peerRequestQueue.Pop()
case <-e.ticker.C:
e.peerRequestQueue.thawRound()
nextTask = e.peerRequestQueue.Pop()
}
}
// with a task in hand, we're ready to prepare the envelope...
block, err := e.bs.Get(nextTask.Entry.Key)
if err != nil {
// If we don't have the block, don't hold that against the peer
// make sure to update that the task has been 'completed'
nextTask.Done()
continue
}
return &Envelope{
Peer: nextTask.Target,
Block: block,
Sent: func() {
nextTask.Done()
select {
case e.workSignal <- struct{}{}:
// work completing may mean that our queue will provide new
// work to be done.
default:
}
},
}, nil
}
}
// Outbox returns a channel of one-time use Envelope channels.
func (e *Engine) Outbox() <-chan (<-chan *Envelope) {
return e.outbox
}
// Returns a slice of Peers with whom the local node has active sessions
func (e *Engine) Peers() []peer.ID {
e.lock.Lock()
defer e.lock.Unlock()
response := make([]peer.ID, 0)
for _, ledger := range e.ledgerMap {
response = append(response, ledger.Partner)
}
return response
}
// MessageReceived performs book-keeping. Returns error if passed invalid
// arguments.
func (e *Engine) MessageReceived(p peer.ID, m bsmsg.BitSwapMessage) error {
if len(m.Wantlist()) == 0 && len(m.Blocks()) == 0 {
log.Debugf("received empty message from %s", p)
}
newWorkExists := false
defer func() {
if newWorkExists {
e.signalNewWork()
}
}()
l := e.findOrCreate(p)
l.lk.Lock()
defer l.lk.Unlock()
if m.Full() {
l.wantList = wl.New()
}
for _, entry := range m.Wantlist() {
if entry.Cancel {
log.Debugf("cancel %s", entry.Key)
l.CancelWant(entry.Key)
e.peerRequestQueue.Remove(entry.Key, p)
} else {
log.Debugf("wants %s - %d", entry.Key, entry.Priority)
l.Wants(entry.Key, entry.Priority)
if exists, err := e.bs.Has(entry.Key); err == nil && exists {
e.peerRequestQueue.Push(entry.Entry, p)
newWorkExists = true
}
}
}
for _, block := range m.Blocks() {
log.Debugf("got block %s %d bytes", block.Key(), len(block.Data()))
l.ReceivedBytes(len(block.Data()))
}
return nil
}
func (e *Engine) addBlock(block blocks.Block) {
work := false
for _, l := range e.ledgerMap {
l.lk.Lock()
if entry, ok := l.WantListContains(block.Key()); ok {
e.peerRequestQueue.Push(entry, l.Partner)
work = true
}
l.lk.Unlock()
}
if work {
e.signalNewWork()
}
}
func (e *Engine) AddBlock(block blocks.Block) {
e.lock.Lock()
defer e.lock.Unlock()
e.addBlock(block)
}
// TODO add contents of m.WantList() to my local wantlist? NB: could introduce
// race conditions where I send a message, but MessageSent gets handled after
// MessageReceived. The information in the local wantlist could become
// inconsistent. Would need to ensure that Sends and acknowledgement of the
// send happen atomically
func (e *Engine) MessageSent(p peer.ID, m bsmsg.BitSwapMessage) error {
l := e.findOrCreate(p)
for _, block := range m.Blocks() {
l.SentBytes(len(block.Data()))
l.wantList.Remove(block.Key())
e.peerRequestQueue.Remove(block.Key(), p)
}
return nil
}
func (e *Engine) PeerDisconnected(p peer.ID) {
// TODO: release ledger
}
func (e *Engine) numBytesSentTo(p peer.ID) uint64 {
// NB not threadsafe
return e.findOrCreate(p).Accounting.BytesSent
}
func (e *Engine) numBytesReceivedFrom(p peer.ID) uint64 {
// NB not threadsafe
return e.findOrCreate(p).Accounting.BytesRecv
}
// ledger lazily instantiates a ledger
func (e *Engine) findOrCreate(p peer.ID) *ledger {
e.lock.Lock()
l, ok := e.ledgerMap[p]
if !ok {
l = newLedger(p)
e.ledgerMap[p] = l
}
e.lock.Unlock()
return l
}
func (e *Engine) signalNewWork() {
// Signal task generation to restart (if stopped!)
select {
case e.workSignal <- struct{}{}:
default:
}
}