2016-08-29 19:18:00 +00:00
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// Copyright 2016 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package storage
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import (
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"context"
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"encoding/hex"
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"fmt"
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"sync"
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"sync/atomic"
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"time"
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"github.com/ethereum/go-ethereum/p2p/discover"
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"github.com/ethereum/go-ethereum/swarm/log"
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lru "github.com/hashicorp/golang-lru"
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)
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type (
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NewNetFetcherFunc func(ctx context.Context, addr Address, peers *sync.Map) NetFetcher
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)
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type NetFetcher interface {
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Request(ctx context.Context)
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Offer(ctx context.Context, source *discover.NodeID)
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}
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// NetStore is an extension of local storage
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// it implements the ChunkStore interface
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// on request it initiates remote cloud retrieval using a fetcher
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// fetchers are unique to a chunk and are stored in fetchers LRU memory cache
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// fetchFuncFactory is a factory object to create a fetch function for a specific chunk address
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type NetStore struct {
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mu sync.Mutex
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store SyncChunkStore
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fetchers *lru.Cache
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NewNetFetcherFunc NewNetFetcherFunc
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closeC chan struct{}
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}
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// NewNetStore creates a new NetStore object using the given local store. newFetchFunc is a
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// constructor function that can create a fetch function for a specific chunk address.
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func NewNetStore(store SyncChunkStore, nnf NewNetFetcherFunc) (*NetStore, error) {
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fetchers, err := lru.New(defaultChunkRequestsCacheCapacity)
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if err != nil {
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return nil, err
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}
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return &NetStore{
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store: store,
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fetchers: fetchers,
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NewNetFetcherFunc: nnf,
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closeC: make(chan struct{}),
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}, nil
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}
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// Put stores a chunk in localstore, and delivers to all requestor peers using the fetcher stored in
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// the fetchers cache
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func (n *NetStore) Put(ctx context.Context, ch Chunk) error {
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n.mu.Lock()
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defer n.mu.Unlock()
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// put to the chunk to the store, there should be no error
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err := n.store.Put(ctx, ch)
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if err != nil {
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return err
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}
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// if chunk is now put in the store, check if there was an active fetcher and call deliver on it
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// (this delivers the chunk to requestors via the fetcher)
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if f := n.getFetcher(ch.Address()); f != nil {
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f.deliver(ctx, ch)
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}
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return nil
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}
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// Get retrieves the chunk from the NetStore DPA synchronously.
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// It calls NetStore.get, and if the chunk is not in local Storage
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// it calls fetch with the request, which blocks until the chunk
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// arrived or context is done
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func (n *NetStore) Get(rctx context.Context, ref Address) (Chunk, error) {
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chunk, fetch, err := n.get(rctx, ref)
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if err != nil {
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return nil, err
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}
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if chunk != nil {
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return chunk, nil
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}
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return fetch(rctx)
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}
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func (n *NetStore) BinIndex(po uint8) uint64 {
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return n.store.BinIndex(po)
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}
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func (n *NetStore) Iterator(from uint64, to uint64, po uint8, f func(Address, uint64) bool) error {
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return n.store.Iterator(from, to, po, f)
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}
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// FetchFunc returns nil if the store contains the given address. Otherwise it returns a wait function,
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// which returns after the chunk is available or the context is done
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func (n *NetStore) FetchFunc(ctx context.Context, ref Address) func(context.Context) error {
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chunk, fetch, _ := n.get(ctx, ref)
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if chunk != nil {
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return nil
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}
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return func(ctx context.Context) error {
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_, err := fetch(ctx)
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return err
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}
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}
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// Close chunk store
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func (n *NetStore) Close() {
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close(n.closeC)
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n.store.Close()
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// TODO: loop through fetchers to cancel them
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}
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// get attempts at retrieving the chunk from LocalStore
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// If it is not found then using getOrCreateFetcher:
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// 1. Either there is already a fetcher to retrieve it
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// 2. A new fetcher is created and saved in the fetchers cache
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// From here on, all Get will hit on this fetcher until the chunk is delivered
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// or all fetcher contexts are done.
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// It returns a chunk, a fetcher function and an error
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// If chunk is nil, the returned fetch function needs to be called with a context to return the chunk.
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func (n *NetStore) get(ctx context.Context, ref Address) (Chunk, func(context.Context) (Chunk, error), error) {
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n.mu.Lock()
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defer n.mu.Unlock()
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chunk, err := n.store.Get(ctx, ref)
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if err != nil {
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if err != ErrChunkNotFound {
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log.Debug("Received error from LocalStore other than ErrNotFound", "err", err)
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}
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// The chunk is not available in the LocalStore, let's get the fetcher for it, or create a new one
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// if it doesn't exist yet
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f := n.getOrCreateFetcher(ref)
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// If the caller needs the chunk, it has to use the returned fetch function to get it
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return nil, f.Fetch, nil
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}
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return chunk, nil, nil
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}
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// getOrCreateFetcher attempts at retrieving an existing fetchers
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// if none exists, creates one and saves it in the fetchers cache
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// caller must hold the lock
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func (n *NetStore) getOrCreateFetcher(ref Address) *fetcher {
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if f := n.getFetcher(ref); f != nil {
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return f
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}
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// no fetcher for the given address, we have to create a new one
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key := hex.EncodeToString(ref)
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// create the context during which fetching is kept alive
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ctx, cancel := context.WithCancel(context.Background())
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// destroy is called when all requests finish
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destroy := func() {
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// remove fetcher from fetchers
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n.fetchers.Remove(key)
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// stop fetcher by cancelling context called when
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// all requests cancelled/timedout or chunk is delivered
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cancel()
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}
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// peers always stores all the peers which have an active request for the chunk. It is shared
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// between fetcher and the NewFetchFunc function. It is needed by the NewFetchFunc because
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// the peers which requested the chunk should not be requested to deliver it.
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peers := &sync.Map{}
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fetcher := newFetcher(ref, n.NewNetFetcherFunc(ctx, ref, peers), destroy, peers, n.closeC)
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n.fetchers.Add(key, fetcher)
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return fetcher
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}
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// getFetcher retrieves the fetcher for the given address from the fetchers cache if it exists,
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// otherwise it returns nil
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func (n *NetStore) getFetcher(ref Address) *fetcher {
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key := hex.EncodeToString(ref)
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f, ok := n.fetchers.Get(key)
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if ok {
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return f.(*fetcher)
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}
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return nil
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}
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// RequestsCacheLen returns the current number of outgoing requests stored in the cache
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func (n *NetStore) RequestsCacheLen() int {
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return n.fetchers.Len()
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}
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// One fetcher object is responsible to fetch one chunk for one address, and keep track of all the
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// peers who have requested it and did not receive it yet.
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type fetcher struct {
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addr Address // address of chunk
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chunk Chunk // fetcher can set the chunk on the fetcher
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deliveredC chan struct{} // chan signalling chunk delivery to requests
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cancelledC chan struct{} // chan signalling the fetcher has been cancelled (removed from fetchers in NetStore)
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netFetcher NetFetcher // remote fetch function to be called with a request source taken from the context
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cancel func() // cleanup function for the remote fetcher to call when all upstream contexts are called
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peers *sync.Map // the peers which asked for the chunk
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requestCnt int32 // number of requests on this chunk. If all the requests are done (delivered or context is done) the cancel function is called
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deliverOnce *sync.Once // guarantees that we only close deliveredC once
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}
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// newFetcher creates a new fetcher object for the fiven addr. fetch is the function which actually
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// does the retrieval (in non-test cases this is coming from the network package). cancel function is
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// called either
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// 1. when the chunk has been fetched all peers have been either notified or their context has been done
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// 2. the chunk has not been fetched but all context from all the requests has been done
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// The peers map stores all the peers which have requested chunk.
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func newFetcher(addr Address, nf NetFetcher, cancel func(), peers *sync.Map, closeC chan struct{}) *fetcher {
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cancelOnce := &sync.Once{} // cancel should only be called once
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return &fetcher{
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addr: addr,
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deliveredC: make(chan struct{}),
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deliverOnce: &sync.Once{},
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cancelledC: closeC,
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netFetcher: nf,
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cancel: func() {
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cancelOnce.Do(func() {
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cancel()
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})
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},
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peers: peers,
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}
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}
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// Fetch fetches the chunk synchronously, it is called by NetStore.Get is the chunk is not available
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// locally.
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func (f *fetcher) Fetch(rctx context.Context) (Chunk, error) {
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atomic.AddInt32(&f.requestCnt, 1)
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defer func() {
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// if all the requests are done the fetcher can be cancelled
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if atomic.AddInt32(&f.requestCnt, -1) == 0 {
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f.cancel()
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}
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}()
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// The peer asking for the chunk. Store in the shared peers map, but delete after the request
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// has been delivered
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peer := rctx.Value("peer")
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if peer != nil {
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f.peers.Store(peer, time.Now())
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defer f.peers.Delete(peer)
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}
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// If there is a source in the context then it is an offer, otherwise a request
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sourceIF := rctx.Value("source")
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if sourceIF != nil {
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var source *discover.NodeID
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id := discover.MustHexID(sourceIF.(string))
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source = &id
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f.netFetcher.Offer(rctx, source)
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} else {
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f.netFetcher.Request(rctx)
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}
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// wait until either the chunk is delivered or the context is done
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select {
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case <-rctx.Done():
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return nil, rctx.Err()
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case <-f.deliveredC:
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return f.chunk, nil
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case <-f.cancelledC:
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return nil, fmt.Errorf("fetcher cancelled")
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}
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}
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// deliver is called by NetStore.Put to notify all pending requests
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func (f *fetcher) deliver(ctx context.Context, ch Chunk) {
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f.deliverOnce.Do(func() {
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f.chunk = ch
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// closing the deliveredC channel will terminate ongoing requests
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close(f.deliveredC)
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})
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}
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