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online.go
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online.go
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// Copyright (C) 2019 Storj Labs, Inc.
// See LICENSE for copying information.
package checker
import (
"context"
"sync"
"sync/atomic"
"time"
"storj.io/common/pb"
"storj.io/common/storj"
"storj.io/storj/satellite/overlay"
)
// ReliabilityCache caches the reliable nodes for the specified staleness duration
// and updates automatically from overlay.
//
// architecture: Service
type ReliabilityCache struct {
overlay *overlay.Service
staleness time.Duration
mu sync.Mutex
state atomic.Value // contains immutable *reliabilityState
}
// reliabilityState
type reliabilityState struct {
reliable map[storj.NodeID]struct{}
created time.Time
}
// NewReliabilityCache creates a new reliability checking cache.
func NewReliabilityCache(overlay *overlay.Service, staleness time.Duration) *ReliabilityCache {
return &ReliabilityCache{
overlay: overlay,
staleness: staleness,
}
}
// LastUpdate returns when the cache was last updated.
func (cache *ReliabilityCache) LastUpdate() time.Time {
if state, ok := cache.state.Load().(*reliabilityState); ok {
return state.created
}
return time.Time{}
}
// MissingPieces returns piece indices that are unreliable with the given staleness period.
func (cache *ReliabilityCache) MissingPieces(ctx context.Context, created time.Time, pieces []*pb.RemotePiece) (_ []int32, err error) {
defer mon.Task()(&ctx)(&err)
// This code is designed to be very fast in the case where a refresh is not needed: just an
// atomic load from rarely written to bit of shared memory. The general strategy is to first
// read if the state suffices to answer the query. If not (due to it not existing, being
// too stale, etc.), then we acquire the mutex to block other requests that may be stale
// and ensure we only issue one refresh at a time. After acquiring the mutex, we have to
// double check that the state is still stale because some other call may have beat us to
// the acquisition. Only then do we refresh and can then proceed answering the query.
state, ok := cache.state.Load().(*reliabilityState)
if !ok || created.After(state.created) || time.Since(state.created) > cache.staleness {
cache.mu.Lock()
state, ok = cache.state.Load().(*reliabilityState)
if !ok || created.After(state.created) || time.Since(state.created) > cache.staleness {
state, err = cache.refreshLocked(ctx)
}
cache.mu.Unlock()
if err != nil {
return nil, err
}
}
var unreliable []int32
for _, piece := range pieces {
if _, ok := state.reliable[piece.NodeId]; !ok {
unreliable = append(unreliable, piece.PieceNum)
}
}
return unreliable, nil
}
// Refresh refreshes the cache.
func (cache *ReliabilityCache) Refresh(ctx context.Context) (err error) {
defer mon.Task()(&ctx)(&err)
cache.mu.Lock()
defer cache.mu.Unlock()
_, err = cache.refreshLocked(ctx)
return err
}
// refreshLocked does the refreshes assuming the write mutex is held.
func (cache *ReliabilityCache) refreshLocked(ctx context.Context) (_ *reliabilityState, err error) {
defer mon.Task()(&ctx)(&err)
nodes, err := cache.overlay.Reliable(ctx)
if err != nil {
return nil, Error.Wrap(err)
}
state := &reliabilityState{
created: time.Now(),
reliable: make(map[storj.NodeID]struct{}, len(nodes)),
}
for _, id := range nodes {
state.reliable[id] = struct{}{}
}
cache.state.Store(state)
return state, nil
}