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swap, swap/chain: add transaction queue
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,105 @@ | ||
| package chain | ||
|
|
||
| import ( | ||
| "context" | ||
| "encoding" | ||
| "encoding/json" | ||
| "strconv" | ||
| "strings" | ||
| "sync" | ||
| "time" | ||
|
|
||
| "github.com/ethersphere/swarm/state" | ||
| ) | ||
|
|
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| // PersistentQueue represents a queue stored in a state store | ||
| type PersistentQueue struct { | ||
| lock sync.Mutex | ||
| store state.Store | ||
| prefix string | ||
| trigger chan struct{} | ||
| nonce uint64 | ||
| } | ||
|
|
||
| // NewPersistentQueue creates a structure to interact with a queue with the given prefix | ||
| func NewPersistentQueue(store state.Store, prefix string) *PersistentQueue { | ||
| return &PersistentQueue{ | ||
| store: store, | ||
| prefix: prefix, | ||
| trigger: make(chan struct{}, 1), | ||
| nonce: 0, | ||
| } | ||
| } | ||
|
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| // Queue puts the necessary database operations for the queueing into the supplied batch | ||
| // it returns the generated key and a trigger function which must be called if the batch was successfully written | ||
| // this only returns an error if the encoding fails which is an unrecoverable error | ||
| func (pq *PersistentQueue) Queue(b *state.StoreBatch, v interface{}) (key string, trigger func(), err error) { | ||
| pq.lock.Lock() | ||
| defer pq.lock.Unlock() | ||
|
|
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| pq.nonce++ | ||
| key = time.Now().String() + "_" + strconv.FormatUint(pq.nonce, 10) | ||
| if err = b.Put(pq.prefix+key, v); err != nil { | ||
| return "", nil, err | ||
| } | ||
|
|
||
| return key, func() { | ||
| select { | ||
| case pq.trigger <- struct{}{}: | ||
| default: | ||
| } | ||
| }, nil | ||
| } | ||
|
|
||
| // Peek looks at the next item in the queue | ||
| // the error returned is either an decode or an io error | ||
| func (pq *PersistentQueue) Peek(i interface{}) (key string, exists bool, err error) { | ||
| err = pq.store.Iterate(pq.prefix, func(k, data []byte) (bool, error) { | ||
| key = string(k) | ||
| unmarshaler, ok := i.(encoding.BinaryUnmarshaler) | ||
| if !ok { | ||
| return true, json.Unmarshal(data, i) | ||
| } | ||
| return true, unmarshaler.UnmarshalBinary(data) | ||
| }) | ||
| if err != nil { | ||
| return "", false, err | ||
| } | ||
| if key == "" { | ||
| return "", false, nil | ||
| } | ||
| return strings.TrimPrefix(key, pq.prefix), true, nil | ||
| } | ||
|
|
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| // Next looks at the next item in the queue and blocks until an item is available if there is none | ||
| // the error returned is either an decode error, an io error or a cancelled context | ||
| func (pq *PersistentQueue) Next(ctx context.Context, i interface{}) (key string, err error) { | ||
| key, exists, err := pq.Peek(i) | ||
| if err != nil { | ||
| return "", err | ||
| } | ||
| if exists { | ||
| return key, nil | ||
| } | ||
|
|
||
| for { | ||
| select { | ||
| case <-pq.trigger: | ||
| key, exists, err = pq.Peek(i) | ||
| if err != nil { | ||
| return "", err | ||
| } | ||
| if exists { | ||
| return key, nil | ||
| } | ||
| case <-ctx.Done(): | ||
| return "", ctx.Err() | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // Delete adds the batch operation to delete the queue element with the given key | ||
| func (pq *PersistentQueue) Delete(b *state.StoreBatch, key string) { | ||
| b.Delete(pq.prefix + key) | ||
| } |
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