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providerquerymanager.go
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providerquerymanager.go
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package providerquerymanager
import (
"context"
"fmt"
"sync"
"time"
"github.com/ipfs/go-cid"
logging "github.com/ipfs/go-log/v2"
peer "github.com/libp2p/go-libp2p/core/peer"
)
var log = logging.Logger("bitswap")
const (
maxProviders = 10
maxInProcessRequests = 6
defaultTimeout = 10 * time.Second
)
type inProgressRequestStatus struct {
ctx context.Context
cancelFn func()
providersSoFar []peer.ID
listeners map[chan peer.ID]struct{}
}
type findProviderRequest struct {
k cid.Cid
ctx context.Context
}
// ProviderQueryNetwork is an interface for finding providers and connecting to
// peers.
type ProviderQueryNetwork interface {
ConnectTo(context.Context, peer.ID) error
FindProvidersAsync(context.Context, cid.Cid, int) <-chan peer.ID
}
type providerQueryMessage interface {
debugMessage() string
handle(pqm *ProviderQueryManager)
}
type receivedProviderMessage struct {
ctx context.Context
k cid.Cid
p peer.ID
}
type finishedProviderQueryMessage struct {
ctx context.Context
k cid.Cid
}
type newProvideQueryMessage struct {
ctx context.Context
k cid.Cid
inProgressRequestChan chan<- inProgressRequest
}
type cancelRequestMessage struct {
incomingProviders chan peer.ID
k cid.Cid
}
// ProviderQueryManager manages requests to find more providers for blocks
// for bitswap sessions. It's main goals are to:
// - rate limit requests -- don't have too many find provider calls running
// simultaneously
// - connect to found peers and filter them if it can't connect
// - ensure two findprovider calls for the same block don't run concurrently
// - manage timeouts
type ProviderQueryManager struct {
ctx context.Context
network ProviderQueryNetwork
providerQueryMessages chan providerQueryMessage
providerRequestsProcessing chan *findProviderRequest
incomingFindProviderRequests chan *findProviderRequest
findProviderTimeout time.Duration
timeoutMutex sync.RWMutex
// do not touch outside the run loop
inProgressRequestStatuses map[cid.Cid]*inProgressRequestStatus
}
// New initializes a new ProviderQueryManager for a given context and a given
// network provider.
func New(ctx context.Context, network ProviderQueryNetwork) *ProviderQueryManager {
return &ProviderQueryManager{
ctx: ctx,
network: network,
providerQueryMessages: make(chan providerQueryMessage, 16),
providerRequestsProcessing: make(chan *findProviderRequest),
incomingFindProviderRequests: make(chan *findProviderRequest),
inProgressRequestStatuses: make(map[cid.Cid]*inProgressRequestStatus),
findProviderTimeout: defaultTimeout,
}
}
// Startup starts processing for the ProviderQueryManager.
func (pqm *ProviderQueryManager) Startup() {
go pqm.run()
}
type inProgressRequest struct {
providersSoFar []peer.ID
incoming chan peer.ID
}
// SetFindProviderTimeout changes the timeout for finding providers
func (pqm *ProviderQueryManager) SetFindProviderTimeout(findProviderTimeout time.Duration) {
pqm.timeoutMutex.Lock()
pqm.findProviderTimeout = findProviderTimeout
pqm.timeoutMutex.Unlock()
}
// FindProvidersAsync finds providers for the given block.
func (pqm *ProviderQueryManager) FindProvidersAsync(sessionCtx context.Context, k cid.Cid) <-chan peer.ID {
inProgressRequestChan := make(chan inProgressRequest)
select {
case pqm.providerQueryMessages <- &newProvideQueryMessage{
ctx: sessionCtx,
k: k,
inProgressRequestChan: inProgressRequestChan,
}:
case <-pqm.ctx.Done():
ch := make(chan peer.ID)
close(ch)
return ch
case <-sessionCtx.Done():
ch := make(chan peer.ID)
close(ch)
return ch
}
// DO NOT select on sessionCtx. We only want to abort here if we're
// shutting down because we can't actually _cancel_ the request till we
// get to receiveProviders.
var receivedInProgressRequest inProgressRequest
select {
case <-pqm.ctx.Done():
ch := make(chan peer.ID)
close(ch)
return ch
case receivedInProgressRequest = <-inProgressRequestChan:
}
return pqm.receiveProviders(sessionCtx, k, receivedInProgressRequest)
}
func (pqm *ProviderQueryManager) receiveProviders(sessionCtx context.Context, k cid.Cid, receivedInProgressRequest inProgressRequest) <-chan peer.ID {
// maintains an unbuffered queue for incoming providers for given request for a given session
// essentially, as a provider comes in, for a given CID, we want to immediately broadcast to all
// sessions that queried that CID, without worrying about whether the client code is actually
// reading from the returned channel -- so that the broadcast never blocks
// based on: https://medium.com/capital-one-tech/building-an-unbounded-channel-in-go-789e175cd2cd
returnedProviders := make(chan peer.ID)
receivedProviders := append([]peer.ID(nil), receivedInProgressRequest.providersSoFar[0:]...)
incomingProviders := receivedInProgressRequest.incoming
go func() {
defer close(returnedProviders)
outgoingProviders := func() chan<- peer.ID {
if len(receivedProviders) == 0 {
return nil
}
return returnedProviders
}
nextProvider := func() peer.ID {
if len(receivedProviders) == 0 {
return ""
}
return receivedProviders[0]
}
for len(receivedProviders) > 0 || incomingProviders != nil {
select {
case <-pqm.ctx.Done():
return
case <-sessionCtx.Done():
if incomingProviders != nil {
pqm.cancelProviderRequest(k, incomingProviders)
}
return
case provider, ok := <-incomingProviders:
if !ok {
incomingProviders = nil
} else {
receivedProviders = append(receivedProviders, provider)
}
case outgoingProviders() <- nextProvider():
receivedProviders = receivedProviders[1:]
}
}
}()
return returnedProviders
}
func (pqm *ProviderQueryManager) cancelProviderRequest(k cid.Cid, incomingProviders chan peer.ID) {
cancelMessageChannel := pqm.providerQueryMessages
for {
select {
case cancelMessageChannel <- &cancelRequestMessage{
incomingProviders: incomingProviders,
k: k,
}:
cancelMessageChannel = nil
// clear out any remaining providers, in case and "incoming provider"
// messages get processed before our cancel message
case _, ok := <-incomingProviders:
if !ok {
return
}
case <-pqm.ctx.Done():
return
}
}
}
func (pqm *ProviderQueryManager) findProviderWorker() {
// findProviderWorker just cycles through incoming provider queries one
// at a time. We have six of these workers running at once
// to let requests go in parallel but keep them rate limited
for {
select {
case fpr, ok := <-pqm.providerRequestsProcessing:
if !ok {
return
}
k := fpr.k
log.Debugf("Beginning Find Provider Request for cid: %s", k.String())
pqm.timeoutMutex.RLock()
findProviderCtx, cancel := context.WithTimeout(fpr.ctx, pqm.findProviderTimeout)
pqm.timeoutMutex.RUnlock()
providers := pqm.network.FindProvidersAsync(findProviderCtx, k, maxProviders)
wg := &sync.WaitGroup{}
for p := range providers {
wg.Add(1)
go func(p peer.ID) {
defer wg.Done()
err := pqm.network.ConnectTo(findProviderCtx, p)
if err != nil {
log.Debugf("failed to connect to provider %s: %s", p, err)
return
}
select {
case pqm.providerQueryMessages <- &receivedProviderMessage{
ctx: findProviderCtx,
k: k,
p: p,
}:
case <-pqm.ctx.Done():
return
}
}(p)
}
wg.Wait()
cancel()
select {
case pqm.providerQueryMessages <- &finishedProviderQueryMessage{
ctx: findProviderCtx,
k: k,
}:
case <-pqm.ctx.Done():
}
case <-pqm.ctx.Done():
return
}
}
}
func (pqm *ProviderQueryManager) providerRequestBufferWorker() {
// the provider request buffer worker just maintains an unbounded
// buffer for incoming provider queries and dispatches to the find
// provider workers as they become available
// based on: https://medium.com/capital-one-tech/building-an-unbounded-channel-in-go-789e175cd2cd
var providerQueryRequestBuffer []*findProviderRequest
nextProviderQuery := func() *findProviderRequest {
if len(providerQueryRequestBuffer) == 0 {
return nil
}
return providerQueryRequestBuffer[0]
}
outgoingRequests := func() chan<- *findProviderRequest {
if len(providerQueryRequestBuffer) == 0 {
return nil
}
return pqm.providerRequestsProcessing
}
for {
select {
case incomingRequest, ok := <-pqm.incomingFindProviderRequests:
if !ok {
return
}
providerQueryRequestBuffer = append(providerQueryRequestBuffer, incomingRequest)
case outgoingRequests() <- nextProviderQuery():
providerQueryRequestBuffer = providerQueryRequestBuffer[1:]
case <-pqm.ctx.Done():
return
}
}
}
func (pqm *ProviderQueryManager) cleanupInProcessRequests() {
for _, requestStatus := range pqm.inProgressRequestStatuses {
for listener := range requestStatus.listeners {
close(listener)
}
requestStatus.cancelFn()
}
}
func (pqm *ProviderQueryManager) run() {
defer pqm.cleanupInProcessRequests()
go pqm.providerRequestBufferWorker()
for i := 0; i < maxInProcessRequests; i++ {
go pqm.findProviderWorker()
}
for {
select {
case nextMessage := <-pqm.providerQueryMessages:
log.Debug(nextMessage.debugMessage())
nextMessage.handle(pqm)
case <-pqm.ctx.Done():
return
}
}
}
func (rpm *receivedProviderMessage) debugMessage() string {
return fmt.Sprintf("Received provider (%s) for cid (%s)", rpm.p.String(), rpm.k.String())
}
func (rpm *receivedProviderMessage) handle(pqm *ProviderQueryManager) {
requestStatus, ok := pqm.inProgressRequestStatuses[rpm.k]
if !ok {
log.Errorf("Received provider (%s) for cid (%s) not requested", rpm.p.String(), rpm.k.String())
return
}
requestStatus.providersSoFar = append(requestStatus.providersSoFar, rpm.p)
for listener := range requestStatus.listeners {
select {
case listener <- rpm.p:
case <-pqm.ctx.Done():
return
}
}
}
func (fpqm *finishedProviderQueryMessage) debugMessage() string {
return fmt.Sprintf("Finished Provider Query on cid: %s", fpqm.k.String())
}
func (fpqm *finishedProviderQueryMessage) handle(pqm *ProviderQueryManager) {
requestStatus, ok := pqm.inProgressRequestStatuses[fpqm.k]
if !ok {
// we canceled the request as it finished.
return
}
for listener := range requestStatus.listeners {
close(listener)
}
delete(pqm.inProgressRequestStatuses, fpqm.k)
requestStatus.cancelFn()
}
func (npqm *newProvideQueryMessage) debugMessage() string {
return fmt.Sprintf("New Provider Query on cid: %s", npqm.k.String())
}
func (npqm *newProvideQueryMessage) handle(pqm *ProviderQueryManager) {
requestStatus, ok := pqm.inProgressRequestStatuses[npqm.k]
if !ok {
ctx, cancelFn := context.WithCancel(pqm.ctx)
requestStatus = &inProgressRequestStatus{
listeners: make(map[chan peer.ID]struct{}),
ctx: ctx,
cancelFn: cancelFn,
}
pqm.inProgressRequestStatuses[npqm.k] = requestStatus
select {
case pqm.incomingFindProviderRequests <- &findProviderRequest{
k: npqm.k,
ctx: ctx,
}:
case <-pqm.ctx.Done():
return
}
}
inProgressChan := make(chan peer.ID)
requestStatus.listeners[inProgressChan] = struct{}{}
select {
case npqm.inProgressRequestChan <- inProgressRequest{
providersSoFar: requestStatus.providersSoFar,
incoming: inProgressChan,
}:
case <-pqm.ctx.Done():
}
}
func (crm *cancelRequestMessage) debugMessage() string {
return fmt.Sprintf("Cancel provider query on cid: %s", crm.k.String())
}
func (crm *cancelRequestMessage) handle(pqm *ProviderQueryManager) {
requestStatus, ok := pqm.inProgressRequestStatuses[crm.k]
if !ok {
// Request finished while queued.
return
}
_, ok = requestStatus.listeners[crm.incomingProviders]
if !ok {
// Request finished and _restarted_ while queued.
return
}
delete(requestStatus.listeners, crm.incomingProviders)
close(crm.incomingProviders)
if len(requestStatus.listeners) == 0 {
delete(pqm.inProgressRequestStatuses, crm.k)
requestStatus.cancelFn()
}
}