aboutsummaryrefslogtreecommitdiffstats
path: root/core/tx_pool.go
blob: 2c8a5c396c53a8118324434f1ff266cb0dac1f48 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package core

import (
    "errors"
    "fmt"
    "math/big"
    "sort"
    "sync"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/state"
    "github.com/ethereum/go-ethereum/core/types"
    "github.com/ethereum/go-ethereum/event"
    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
    "gopkg.in/karalabe/cookiejar.v2/collections/prque"
)

var (
    // Transaction Pool Errors
    ErrInvalidSender      = errors.New("Invalid sender")
    ErrNonce              = errors.New("Nonce too low")
    ErrCheap              = errors.New("Gas price too low for acceptance")
    ErrBalance            = errors.New("Insufficient balance")
    ErrNonExistentAccount = errors.New("Account does not exist or account balance too low")
    ErrInsufficientFunds  = errors.New("Insufficient funds for gas * price + value")
    ErrIntrinsicGas       = errors.New("Intrinsic gas too low")
    ErrGasLimit           = errors.New("Exceeds block gas limit")
    ErrNegativeValue      = errors.New("Negative value")
)

var (
    minPendingPerAccount = uint64(16)    // Min number of guaranteed transaction slots per address
    maxPendingTotal      = uint64(4096)  // Max limit of pending transactions from all accounts (soft)
    maxQueuedPerAccount  = uint64(64)    // Max limit of queued transactions per address
    maxQueuedInTotal     = uint64(1024)  // Max limit of queued transactions from all accounts
    maxQueuedLifetime    = 3 * time.Hour // Max amount of time transactions from idle accounts are queued
    evictionInterval     = time.Minute   // Time interval to check for evictable transactions
)

type stateFn func() (*state.StateDB, error)

// TxPool contains all currently known transactions. Transactions
// enter the pool when they are received from the network or submitted
// locally. They exit the pool when they are included in the blockchain.
//
// The pool separates processable transactions (which can be applied to the
// current state) and future transactions. Transactions move between those
// two states over time as they are received and processed.
type TxPool struct {
    config       *ChainConfig
    currentState stateFn // The state function which will allow us to do some pre checks
    pendingState *state.ManagedState
    gasLimit     func() *big.Int // The current gas limit function callback
    minGasPrice  *big.Int
    eventMux     *event.TypeMux
    events       event.Subscription
    localTx      *txSet
    mu           sync.RWMutex

    pending map[common.Address]*txList         // All currently processable transactions
    queue   map[common.Address]*txList         // Queued but non-processable transactions
    all     map[common.Hash]*types.Transaction // All transactions to allow lookups
    beats   map[common.Address]time.Time       // Last heartbeat from each known account

    wg   sync.WaitGroup // for shutdown sync
    quit chan struct{}

    homestead bool
}

func NewTxPool(config *ChainConfig, eventMux *event.TypeMux, currentStateFn stateFn, gasLimitFn func() *big.Int) *TxPool {
    pool := &TxPool{
        config:       config,
        pending:      make(map[common.Address]*txList),
        queue:        make(map[common.Address]*txList),
        all:          make(map[common.Hash]*types.Transaction),
        beats:        make(map[common.Address]time.Time),
        eventMux:     eventMux,
        currentState: currentStateFn,
        gasLimit:     gasLimitFn,
        minGasPrice:  new(big.Int),
        pendingState: nil,
        localTx:      newTxSet(),
        events:       eventMux.Subscribe(ChainHeadEvent{}, GasPriceChanged{}, RemovedTransactionEvent{}),
        quit:         make(chan struct{}),
    }

    pool.wg.Add(2)
    go pool.eventLoop()
    go pool.expirationLoop()

    return pool
}

func (pool *TxPool) eventLoop() {
    defer pool.wg.Done()

    // Track chain events. When a chain events occurs (new chain canon block)
    // we need to know the new state. The new state will help us determine
    // the nonces in the managed state
    for ev := range pool.events.Chan() {
        switch ev := ev.Data.(type) {
        case ChainHeadEvent:
            pool.mu.Lock()
            if ev.Block != nil && pool.config.IsHomestead(ev.Block.Number()) {
                pool.homestead = true
            }

            pool.resetState()
            pool.mu.Unlock()
        case GasPriceChanged:
            pool.mu.Lock()
            pool.minGasPrice = ev.Price
            pool.mu.Unlock()
        case RemovedTransactionEvent:
            pool.AddBatch(ev.Txs)
        }
    }
}

func (pool *TxPool) resetState() {
    currentState, err := pool.currentState()
    if err != nil {
        glog.V(logger.Error).Infof("Failed to get current state: %v", err)
        return
    }
    managedState := state.ManageState(currentState)
    if err != nil {
        glog.V(logger.Error).Infof("Failed to get managed state: %v", err)
        return
    }
    pool.pendingState = managedState

    // validate the pool of pending transactions, this will remove
    // any transactions that have been included in the block or
    // have been invalidated because of another transaction (e.g.
    // higher gas price)
    pool.demoteUnexecutables()

    // Update all accounts to the latest known pending nonce
    for addr, list := range pool.pending {
        txs := list.Flatten() // Heavy but will be cached and is needed by the miner anyway
        pool.pendingState.SetNonce(addr, txs[len(txs)-1].Nonce()+1)
    }
    // Check the queue and move transactions over to the pending if possible
    // or remove those that have become invalid
    pool.promoteExecutables()
}

func (pool *TxPool) Stop() {
    pool.events.Unsubscribe()
    close(pool.quit)
    pool.wg.Wait()
    glog.V(logger.Info).Infoln("Transaction pool stopped")
}

func (pool *TxPool) State() *state.ManagedState {
    pool.mu.RLock()
    defer pool.mu.RUnlock()

    return pool.pendingState
}

// Stats retrieves the current pool stats, namely the number of pending and the
// number of queued (non-executable) transactions.
func (pool *TxPool) Stats() (pending int, queued int) {
    pool.mu.RLock()
    defer pool.mu.RUnlock()

    for _, list := range pool.pending {
        pending += list.Len()
    }
    for _, list := range pool.queue {
        queued += list.Len()
    }
    return
}

// Content retrieves the data content of the transaction pool, returning all the
// pending as well as queued transactions, grouped by account and sorted by nonce.
func (pool *TxPool) Content() (map[common.Address]types.Transactions, map[common.Address]types.Transactions) {
    pool.mu.RLock()
    defer pool.mu.RUnlock()

    pending := make(map[common.Address]types.Transactions)
    for addr, list := range pool.pending {
        pending[addr] = list.Flatten()
    }
    queued := make(map[common.Address]types.Transactions)
    for addr, list := range pool.queue {
        queued[addr] = list.Flatten()
    }
    return pending, queued
}

// Pending retrieves all currently processable transactions, groupped by origin
// account and sorted by nonce. The returned transaction set is a copy and can be
// freely modified by calling code.
func (pool *TxPool) Pending() map[common.Address]types.Transactions {
    pool.mu.Lock()
    defer pool.mu.Unlock()

    // check queue first
    pool.promoteExecutables()

    // invalidate any txs
    pool.demoteUnexecutables()

    pending := make(map[common.Address]types.Transactions)
    for addr, list := range pool.pending {
        pending[addr] = list.Flatten()
    }
    return pending
}

// SetLocal marks a transaction as local, skipping gas price
//  check against local miner minimum in the future
func (pool *TxPool) SetLocal(tx *types.Transaction) {
    pool.mu.Lock()
    defer pool.mu.Unlock()
    pool.localTx.add(tx.Hash())
}

// validateTx checks whether a transaction is valid according
// to the consensus rules.
func (pool *TxPool) validateTx(tx *types.Transaction) error {
    local := pool.localTx.contains(tx.Hash())
    // Drop transactions under our own minimal accepted gas price
    if !local && pool.minGasPrice.Cmp(tx.GasPrice()) > 0 {
        return ErrCheap
    }

    currentState, err := pool.currentState()
    if err != nil {
        return err
    }

    from, err := tx.From()
    if err != nil {
        return ErrInvalidSender
    }

    // Make sure the account exist. Non existent accounts
    // haven't got funds and well therefor never pass.
    if !currentState.Exist(from) {
        return ErrNonExistentAccount
    }

    // Last but not least check for nonce errors
    if currentState.GetNonce(from) > tx.Nonce() {
        return ErrNonce
    }

    // Check the transaction doesn't exceed the current
    // block limit gas.
    if pool.gasLimit().Cmp(tx.Gas()) < 0 {
        return ErrGasLimit
    }

    // Transactions can't be negative. This may never happen
    // using RLP decoded transactions but may occur if you create
    // a transaction using the RPC for example.
    if tx.Value().Cmp(common.Big0) < 0 {
        return ErrNegativeValue
    }

    // Transactor should have enough funds to cover the costs
    // cost == V + GP * GL
    if currentState.GetBalance(from).Cmp(tx.Cost()) < 0 {
        return ErrInsufficientFunds
    }

    intrGas := IntrinsicGas(tx.Data(), MessageCreatesContract(tx), pool.homestead)
    if tx.Gas().Cmp(intrGas) < 0 {
        return ErrIntrinsicGas
    }

    return nil
}

// add validates a transaction and inserts it into the non-executable queue for
// later pending promotion and execution.
func (pool *TxPool) add(tx *types.Transaction) error {
    // If the transaction is alreayd known, discard it
    hash := tx.Hash()
    if pool.all[hash] != nil {
        return fmt.Errorf("Known transaction: %x", hash[:4])
    }
    // Otherwise ensure basic validation passes and queue it up
    if err := pool.validateTx(tx); err != nil {
        return err
    }
    pool.enqueueTx(hash, tx)

    // Print a log message if low enough level is set
    if glog.V(logger.Debug) {
        rcpt := "[NEW_CONTRACT]"
        if to := tx.To(); to != nil {
            rcpt = common.Bytes2Hex(to[:4])
        }
        from, _ := tx.From() // from already verified during tx validation
        glog.Infof("(t) 0x%x => %s (%v) %x\n", from[:4], rcpt, tx.Value, hash)
    }
    return nil
}

// enqueueTx inserts a new transaction into the non-executable transaction queue.
//
// Note, this method assumes the pool lock is held!
func (pool *TxPool) enqueueTx(hash common.Hash, tx *types.Transaction) {
    // Try to insert the transaction into the future queue
    from, _ := tx.From() // already validated
    if pool.queue[from] == nil {
        pool.queue[from] = newTxList(false)
    }
    inserted, old := pool.queue[from].Add(tx)
    if !inserted {
        return // An older transaction was better, discard this
    }
    // Discard any previous transaction and mark this
    if old != nil {
        delete(pool.all, old.Hash())
    }
    pool.all[hash] = tx
}

// promoteTx adds a transaction to the pending (processable) list of transactions.
//
// Note, this method assumes the pool lock is held!
func (pool *TxPool) promoteTx(addr common.Address, hash common.Hash, tx *types.Transaction) {
    // Init delayed since tx pool could have been started before any state sync
    if pool.pendingState == nil {
        pool.resetState()
    }
    // Try to insert the transaction into the pending queue
    if pool.pending[addr] == nil {
        pool.pending[addr] = newTxList(true)
    }
    list := pool.pending[addr]

    inserted, old := list.Add(tx)
    if !inserted {
        // An older transaction was better, discard this
        delete(pool.all, hash)
        return
    }
    // Otherwise discard any previous transaction and mark this
    if old != nil {
        delete(pool.all, old.Hash())
    }
    pool.all[hash] = tx // Failsafe to work around direct pending inserts (tests)

    // Set the potentially new pending nonce and notify any subsystems of the new tx
    pool.beats[addr] = time.Now()
    pool.pendingState.SetNonce(addr, tx.Nonce()+1)
    go pool.eventMux.Post(TxPreEvent{tx})
}

// Add queues a single transaction in the pool if it is valid.
func (pool *TxPool) Add(tx *types.Transaction) error {
    pool.mu.Lock()
    defer pool.mu.Unlock()

    if err := pool.add(tx); err != nil {
        return err
    }
    pool.promoteExecutables()

    return nil
}

// AddBatch attempts to queue a batch of transactions.
func (pool *TxPool) AddBatch(txs []*types.Transaction) {
    pool.mu.Lock()
    defer pool.mu.Unlock()

    for _, tx := range txs {
        if err := pool.add(tx); err != nil {
            glog.V(logger.Debug).Infoln("tx error:", err)
        }
    }
    pool.promoteExecutables()
}

// Get returns a transaction if it is contained in the pool
// and nil otherwise.
func (pool *TxPool) Get(hash common.Hash) *types.Transaction {
    pool.mu.RLock()
    defer pool.mu.RUnlock()

    return pool.all[hash]
}

// Remove removes the transaction with the given hash from the pool.
func (pool *TxPool) Remove(hash common.Hash) {
    pool.mu.Lock()
    defer pool.mu.Unlock()

    pool.removeTx(hash)
}

// RemoveBatch removes all given transactions from the pool.
func (pool *TxPool) RemoveBatch(txs types.Transactions) {
    pool.mu.Lock()
    defer pool.mu.Unlock()

    for _, tx := range txs {
        pool.removeTx(tx.Hash())
    }
}

// removeTx removes a single transaction from the queue, moving all subsequent
// transactions back to the future queue.
func (pool *TxPool) removeTx(hash common.Hash) {
    // Fetch the transaction we wish to delete
    tx, ok := pool.all[hash]
    if !ok {
        return
    }
    addr, _ := tx.From() // already validated during insertion

    // Remove it from the list of known transactions
    delete(pool.all, hash)

    // Remove the transaction from the pending lists and reset the account nonce
    if pending := pool.pending[addr]; pending != nil {
        if removed, invalids := pending.Remove(tx); removed {
            // If no more transactions are left, remove the list
            if pending.Empty() {
                delete(pool.pending, addr)
                delete(pool.beats, addr)
            } else {
                // Otherwise postpone any invalidated transactions
                for _, tx := range invalids {
                    pool.enqueueTx(tx.Hash(), tx)
                }
            }
            // Update the account nonce if needed
            if nonce := tx.Nonce(); pool.pendingState.GetNonce(addr) > nonce {
                pool.pendingState.SetNonce(addr, tx.Nonce())
            }
        }
    }
    // Transaction is in the future queue
    if future := pool.queue[addr]; future != nil {
        future.Remove(tx)
        if future.Empty() {
            delete(pool.queue, addr)
        }
    }
}

// promoteExecutables moves transactions that have become processable from the
// future queue to the set of pending transactions. During this process, all
// invalidated transactions (low nonce, low balance) are deleted.
func (pool *TxPool) promoteExecutables() {
    // Init delayed since tx pool could have been started before any state sync
    if pool.pendingState == nil {
        pool.resetState()
    }
    // Retrieve the current state to allow nonce and balance checking
    state, err := pool.currentState()
    if err != nil {
        glog.Errorf("Could not get current state: %v", err)
        return
    }
    // Iterate over all accounts and promote any executable transactions
    queued := uint64(0)
    for addr, list := range pool.queue {
        // Drop all transactions that are deemed too old (low nonce)
        for _, tx := range list.Forward(state.GetNonce(addr)) {
            if glog.V(logger.Core) {
                glog.Infof("Removed old queued transaction: %v", tx)
            }
            delete(pool.all, tx.Hash())
        }
        // Drop all transactions that are too costly (low balance)
        drops, _ := list.Filter(state.GetBalance(addr))
        for _, tx := range drops {
            if glog.V(logger.Core) {
                glog.Infof("Removed unpayable queued transaction: %v", tx)
            }
            delete(pool.all, tx.Hash())
        }
        // Gather all executable transactions and promote them
        for _, tx := range list.Ready(pool.pendingState.GetNonce(addr)) {
            if glog.V(logger.Core) {
                glog.Infof("Promoting queued transaction: %v", tx)
            }
            pool.promoteTx(addr, tx.Hash(), tx)
        }
        // Drop all transactions over the allowed limit
        for _, tx := range list.Cap(int(maxQueuedPerAccount)) {
            if glog.V(logger.Core) {
                glog.Infof("Removed cap-exceeding queued transaction: %v", tx)
            }
            delete(pool.all, tx.Hash())
        }
        queued += uint64(list.Len())

        // Delete the entire queue entry if it became empty.
        if list.Empty() {
            delete(pool.queue, addr)
        }
    }
    // If the pending limit is overflown, start equalizing allowances
    pending := uint64(0)
    for _, list := range pool.pending {
        pending += uint64(list.Len())
    }
    if pending > maxPendingTotal {
        // Assemble a spam order to penalize large transactors first
        spammers := prque.New()
        for addr, list := range pool.pending {
            // Only evict transactions from high rollers
            if uint64(list.Len()) > minPendingPerAccount {
                // Skip local accounts as pools should maintain backlogs for themselves
                for _, tx := range list.txs.items {
                    if !pool.localTx.contains(tx.Hash()) {
                        spammers.Push(addr, float32(list.Len()))
                    }
                    break // Checking on transaction for locality is enough
                }
            }
        }
        // Gradually drop transactions from offenders
        offenders := []common.Address{}
        for pending > maxPendingTotal && !spammers.Empty() {
            // Retrieve the next offender if not local address
            offender, _ := spammers.Pop()
            offenders = append(offenders, offender.(common.Address))

            // Equalize balances until all the same or below threshold
            if len(offenders) > 1 {
                // Calculate the equalization threshold for all current offenders
                threshold := pool.pending[offender.(common.Address)].Len()

                // Iteratively reduce all offenders until below limit or threshold reached
                for pending > maxPendingTotal && pool.pending[offenders[len(offenders)-2]].Len() > threshold {
                    for i := 0; i < len(offenders)-1; i++ {
                        list := pool.pending[offenders[i]]
                        list.Cap(list.Len() - 1)
                        pending--
                    }
                }
            }
        }
        // If still above threshold, reduce to limit or min allowance
        if pending > maxPendingTotal && len(offenders) > 0 {
            for pending > maxPendingTotal && uint64(pool.pending[offenders[len(offenders)-1]].Len()) > minPendingPerAccount {
                for _, addr := range offenders {
                    list := pool.pending[addr]
                    list.Cap(list.Len() - 1)
                    pending--
                }
            }
        }
    }
    // If we've queued more transactions than the hard limit, drop oldest ones
    if queued > maxQueuedInTotal {
        // Sort all accounts with queued transactions by heartbeat
        addresses := make(addresssByHeartbeat, 0, len(pool.queue))
        for addr, _ := range pool.queue {
            addresses = append(addresses, addressByHeartbeat{addr, pool.beats[addr]})
        }
        sort.Sort(addresses)

        // Drop transactions until the total is below the limit
        for drop := queued - maxQueuedInTotal; drop > 0; {
            addr := addresses[len(addresses)-1]
            list := pool.queue[addr.address]

            addresses = addresses[:len(addresses)-1]

            // Drop all transactions if they are less than the overflow
            if size := uint64(list.Len()); size <= drop {
                for _, tx := range list.Flatten() {
                    pool.removeTx(tx.Hash())
                }
                drop -= size
                continue
            }
            // Otherwise drop only last few transactions
            txs := list.Flatten()
            for i := len(txs) - 1; i >= 0 && drop > 0; i-- {
                pool.removeTx(txs[i].Hash())
                drop--
            }
        }
    }
}

// demoteUnexecutables removes invalid and processed transactions from the pools
// executable/pending queue and any subsequent transactions that become unexecutable
// are moved back into the future queue.
func (pool *TxPool) demoteUnexecutables() {
    // Retrieve the current state to allow nonce and balance checking
    state, err := pool.currentState()
    if err != nil {
        glog.V(logger.Info).Infoln("failed to get current state: %v", err)
        return
    }
    // Iterate over all accounts and demote any non-executable transactions
    for addr, list := range pool.pending {
        nonce := state.GetNonce(addr)

        // Drop all transactions that are deemed too old (low nonce)
        for _, tx := range list.Forward(nonce) {
            if glog.V(logger.Core) {
                glog.Infof("Removed old pending transaction: %v", tx)
            }
            delete(pool.all, tx.Hash())
        }
        // Drop all transactions that are too costly (low balance), and queue any invalids back for later
        drops, invalids := list.Filter(state.GetBalance(addr))
        for _, tx := range drops {
            if glog.V(logger.Core) {
                glog.Infof("Removed unpayable pending transaction: %v", tx)
            }
            delete(pool.all, tx.Hash())
        }
        for _, tx := range invalids {
            if glog.V(logger.Core) {
                glog.Infof("Demoting pending transaction: %v", tx)
            }
            pool.enqueueTx(tx.Hash(), tx)
        }
        // Delete the entire queue entry if it became empty.
        if list.Empty() {
            delete(pool.pending, addr)
            delete(pool.beats, addr)
        }
    }
}

// expirationLoop is a loop that periodically iterates over all accounts with
// queued transactions and drop all that have been inactive for a prolonged amount
// of time.
func (pool *TxPool) expirationLoop() {
    defer pool.wg.Done()

    evict := time.NewTicker(evictionInterval)
    defer evict.Stop()

    for {
        select {
        case <-evict.C:
            pool.mu.Lock()
            for addr := range pool.queue {
                if time.Since(pool.beats[addr]) > maxQueuedLifetime {
                    for _, tx := range pool.queue[addr].Flatten() {
                        pool.removeTx(tx.Hash())
                    }
                }
            }
            pool.mu.Unlock()

        case <-pool.quit:
            return
        }
    }
}

// addressByHeartbeat is an account address tagged with its last activity timestamp.
type addressByHeartbeat struct {
    address   common.Address
    heartbeat time.Time
}

type addresssByHeartbeat []addressByHeartbeat

func (a addresssByHeartbeat) Len() int           { return len(a) }
func (a addresssByHeartbeat) Less(i, j int) bool { return a[i].heartbeat.Before(a[j].heartbeat) }
func (a addresssByHeartbeat) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// txSet represents a set of transaction hashes in which entries
//  are automatically dropped after txSetDuration time
type txSet struct {
    txMap          map[common.Hash]struct{}
    txOrd          map[uint64]txOrdType
    addPtr, delPtr uint64
}

const txSetDuration = time.Hour * 2

// txOrdType represents an entry in the time-ordered list of transaction hashes
type txOrdType struct {
    hash common.Hash
    time time.Time
}

// newTxSet creates a new transaction set
func newTxSet() *txSet {
    return &txSet{
        txMap: make(map[common.Hash]struct{}),
        txOrd: make(map[uint64]txOrdType),
    }
}

// contains returns true if the set contains the given transaction hash
// (not thread safe, should be called from a locked environment)
func (self *txSet) contains(hash common.Hash) bool {
    _, ok := self.txMap[hash]
    return ok
}

// add adds a transaction hash to the set, then removes entries older than txSetDuration
// (not thread safe, should be called from a locked environment)
func (self *txSet) add(hash common.Hash) {
    self.txMap[hash] = struct{}{}
    now := time.Now()
    self.txOrd[self.addPtr] = txOrdType{hash: hash, time: now}
    self.addPtr++
    delBefore := now.Add(-txSetDuration)
    for self.delPtr < self.addPtr && self.txOrd[self.delPtr].time.Before(delBefore) {
        delete(self.txMap, self.txOrd[self.delPtr].hash)
        delete(self.txOrd, self.delPtr)
        self.delPtr++
    }
}