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
use std::fmt;
use std::cmp::Ordering;
use std::collections::{HashMap, HashSet};
use linked_hash_map::LinkedHashMap;
use time::precise_time_s;
use primitives::hash::H256;
use types::PeerIndex;
use utils::AverageSpeedMeter;

/// Max peer failures # before excluding from sync process
const MAX_PEER_FAILURES: usize = 4;
/// Max blocks failures # before forgetiing this block and restarting sync
const MAX_BLOCKS_FAILURES: usize = 6;
/// Number of blocks to inspect while calculating average response time
const BLOCKS_TO_INSPECT: usize = 32;

/// Information on synchronization peers
pub struct Information {
	/// total # of peers.
	pub all: usize,
	/// # of peers that are marked as useful for current synchronization session && have no pending requests.
	pub idle: usize,
	/// # of peers that are marked as non-useful for current synchronization session && have no pending requests.
	pub unuseful: usize,
	/// # of peers that are marked as useful for current synchronization session && have pending requests.
	pub active: usize,
}

/// Set of peers selected for synchronization.
#[derive(Debug, Default)]
pub struct PeersTasks {
	/// All known peers ids
	all: HashSet<PeerIndex>,
	/// All unuseful peers
	unuseful: HashSet<PeerIndex>,
	/// All peers without pending headers requests
	idle_for_headers: HashSet<PeerIndex>,
	/// All peers without pending blocks requests
	idle_for_blocks: HashSet<PeerIndex>,
	/// Pending headers requests sent to peers
	headers_requests: LinkedHashMap<PeerIndex, HeadersRequest>,
	/// Pending blocks requests sent to peers
	blocks_requests: LinkedHashMap<PeerIndex, BlocksRequest>,
	/// Peers statistics
	stats: HashMap<PeerIndex, PeerStats>,
	/// Blocks statistics
	blocks_stats: HashMap<H256, BlockStats>,
}

/// Pending headers request
#[derive(Debug, Clone)]
pub struct HeadersRequest {
	/// Time when request has been sent
	pub timestamp: f64,
}

/// Pending blocks request
#[derive(Debug, Clone)]
pub struct BlocksRequest {
	/// Time when request has been sent
	pub timestamp: f64,
	/// Hashes of blocks that have been requested
	pub blocks: HashSet<H256>,
}

/// Peer trust level.
#[derive(Debug, PartialEq, Clone, Copy)]
pub enum TrustLevel {
	/// Suspicios peer (either it is fresh peer, or it has failed to respond to last requests).
	Suspicious,
	/// This peer is responding to requests.
	Trusted,
}

/// Peer statistics
#[derive(Debug)]
pub struct PeerStats {
	/// Number of blocks requests failures
	failures: usize,
	/// Average block response time meter
	speed: AverageSpeedMeter,
	/// Peer trust level.
	trust: TrustLevel,
}

/// Block statistics
#[derive(Debug, Default)]
struct BlockStats {
	/// Number of block request failures
	failures: usize,
}

impl PeersTasks {
	/// Get information on synchronization peers
	pub fn information(&self) -> Information {
		let active_for_headers: HashSet<_> = self.headers_requests.keys().cloned().collect();
		Information {
			all: self.all.len(),
			idle: self.idle_for_blocks.difference(&active_for_headers).count(),
			unuseful: self.unuseful.len(),
			active: active_for_headers.union(&self.blocks_requests.keys().cloned().collect()).count(),
		}
	}

	/// Get all peers
	pub fn all_peers(&self) -> &HashSet<PeerIndex> {
		&self.all
	}

	/// Get useful peers
	pub fn useful_peers(&self) -> Vec<PeerIndex> {
		self.all.difference(&self.unuseful).cloned().collect()
	}

	/// Get idle peers for headers request.
	pub fn idle_peers_for_headers(&self) -> &HashSet<PeerIndex> {
		&self.idle_for_headers
	}

	/// Get idle peers for blocks request.
	pub fn idle_peers_for_blocks(&self) -> &HashSet<PeerIndex> {
		&self.idle_for_blocks
	}

	/// Sort peers for blocks request
	pub fn sort_peers_for_blocks(&self, peers: &mut Vec<PeerIndex>) {
		peers.sort_by(|left, right| {
			let left_speed = self.stats.get(left).map(|s| s.speed.speed()).unwrap_or(0f64);
			let right_speed = self.stats.get(right).map(|s| s.speed.speed()).unwrap_or(0f64);
			// larger speed => better
			right_speed.partial_cmp(&left_speed).unwrap_or(Ordering::Equal)
		})
	}

	/// Get active headers requests, sorted by last response time (oldest first).
	pub fn ordered_headers_requests(&self) -> &LinkedHashMap<PeerIndex, HeadersRequest> {
		&self.headers_requests
	}

	/// Get active blocks requests, sorted by last response time (oldest first).
	pub fn ordered_blocks_requests(&self) -> &LinkedHashMap<PeerIndex, BlocksRequest> {
		&self.blocks_requests
	}

	/// Get peer tasks
	pub fn get_blocks_tasks(&self, peer_index: PeerIndex) -> Option<&HashSet<H256>> {
		self.blocks_requests
			.get(&peer_index)
			.map(|br| &br.blocks)
	}

	/// Get peer statistics
	pub fn get_peer_stats(&self, peer_index: PeerIndex) -> Option<&PeerStats> {
		self.stats.get(&peer_index)
	}

	/// Mark peer as useful.
	pub fn useful_peer(&mut self, peer_index: PeerIndex) {
		// if peer is unknown => insert to idle queue
		// if peer is known && not useful => insert to idle queue
		if self.all.insert(peer_index)
			|| self.unuseful.remove(&peer_index) {
			self.idle_for_headers.insert(peer_index);
			self.idle_for_blocks.insert(peer_index);
			self.stats.insert(peer_index, PeerStats::new());
		}
	}

	/// Mark peer as unuseful.
	pub fn unuseful_peer(&mut self, peer_index: PeerIndex) {
		// blocks should be rerequested from another peers
		assert!(!self.blocks_requests.contains_key(&peer_index));

		if self.all.insert(peer_index) {
			self.stats.insert(peer_index, PeerStats::new());
		}
		self.unuseful.insert(peer_index);
		self.idle_for_headers.remove(&peer_index);
		self.idle_for_blocks.remove(&peer_index);
	}

	/// Peer has been disconnected
	pub fn disconnect(&mut self, peer_index: PeerIndex) {
		// blocks should be rerequested from another peers
		assert!(!self.blocks_requests.contains_key(&peer_index));

		self.all.remove(&peer_index);
		self.unuseful.remove(&peer_index);
		self.idle_for_headers.remove(&peer_index);
		self.idle_for_blocks.remove(&peer_index);
		self.headers_requests.remove(&peer_index);
		self.blocks_requests.remove(&peer_index);
		self.stats.remove(&peer_index);
	}

	/// Block is received from peer.
	pub fn on_block_received(&mut self, peer_index: PeerIndex, block_hash: &H256) {
		// block received => reset failures
		self.blocks_stats.remove(block_hash);

		let is_last_requested_block_received = if let Some(blocks_request) = self.blocks_requests.get_mut(&peer_index) {
			// if block hasn't been requested => do nothing
			if !blocks_request.blocks.remove(block_hash) {
				return;
			}

			blocks_request.blocks.is_empty()
		} else {
			// this peers hasn't been requested for blocks at all
			return;
		};

		// it was requested block => update block response time
		self.stats.get_mut(&peer_index)
			.map(|br| {
				if br.failures > 0 {
					br.failures -= 1;
				}
				br.trust = TrustLevel::Trusted;
				br.speed.checkpoint()
			});

		// if it hasn't been last requested block => just return
		if !is_last_requested_block_received {
			let mut peer_blocks_requests = self.blocks_requests.remove(&peer_index).expect("checked above; qed");
			peer_blocks_requests.timestamp = precise_time_s();
			self.blocks_requests.insert(peer_index, peer_blocks_requests);
			return;
		}

		// no more requested blocks => pause requests speed meter
		self.stats.get_mut(&peer_index).map(|br| br.speed.stop());

		// mark this peer as idle for blocks request
		self.blocks_requests.remove(&peer_index);
		self.idle_for_blocks.insert(peer_index);
		// also mark as available for headers request if not yet
		if !self.headers_requests.contains_key(&peer_index) {
			self.idle_for_headers.insert(peer_index);
		}
	}

	/// Headers received from peer.
	pub fn on_headers_received(&mut self, peer_index: PeerIndex) {
		self.headers_requests.remove(&peer_index);
		// we only ask for new headers when peer is also not asked for blocks
		// => only insert to idle queue if no active blocks requests
		if !self.blocks_requests.contains_key(&peer_index) {
			self.idle_for_headers.insert(peer_index);
		}
	}

	/// Blocks have been requested from peer.
	pub fn on_blocks_requested(&mut self, peer_index: PeerIndex, blocks_hashes: &[H256]) {
		if !self.all.contains(&peer_index) {
			self.unuseful_peer(peer_index);
		}

		self.unuseful.remove(&peer_index);
		self.idle_for_blocks.remove(&peer_index);

		if !self.blocks_requests.contains_key(&peer_index) {
			self.blocks_requests.insert(peer_index, BlocksRequest::new());
		}
		self.blocks_requests.get_mut(&peer_index)
			.expect("inserted one line above")
			.blocks.extend(blocks_hashes.iter().cloned());

		// no more requested blocks => pause requests speed meter
		self.stats.get_mut(&peer_index).map(|br| br.speed.start());
	}

	/// Headers hashave been requested from peer.
	pub fn on_headers_requested(&mut self, peer_index: PeerIndex) {
		if !self.all.contains(&peer_index) {
			self.unuseful_peer(peer_index);
		}

		self.idle_for_headers.remove(&peer_index);
		self.headers_requests.remove(&peer_index);
		self.headers_requests.insert(peer_index, HeadersRequest::new());
	}

	/// We have failed to get blocks
	pub fn on_blocks_failure(&mut self, hashes: Vec<H256>) -> (Vec<H256>, Vec<H256>) {
		let mut failed_blocks: Vec<H256> = Vec::new();
		let mut normal_blocks: Vec<H256> = Vec::with_capacity(hashes.len());
		for hash in hashes {
			let is_failed_block = {
				let block_stats = self.blocks_stats.entry(hash.clone()).or_insert_with(BlockStats::default);
				block_stats.failures += 1;
				block_stats.failures > MAX_BLOCKS_FAILURES
			};
			if is_failed_block {
				self.blocks_stats.remove(&hash);
				failed_blocks.push(hash);
			} else {
				normal_blocks.push(hash);
			}
		}

		(normal_blocks, failed_blocks)
	}

	/// We have failed to get block from peer during given period
	pub fn on_peer_block_failure(&mut self, peer_index: PeerIndex) -> bool {
		self.stats.get_mut(&peer_index)
			.map(|s| {
				s.failures += 1;
				s.failures > MAX_PEER_FAILURES
			})
			.unwrap_or_default()
	}

	/// We have failed to get headers from peer during given period
	pub fn on_peer_headers_failure(&mut self, peer_index: PeerIndex) -> bool {
		// we never penalize peers for header requests failures
		self.headers_requests.remove(&peer_index);
		self.idle_for_headers.insert(peer_index);

		self.stats.get_mut(&peer_index)
			.map(|s| {
				s.failures += 1;
				s.failures > MAX_PEER_FAILURES
			})
			.unwrap_or_default()
	}

	/// Reset all peers state to the unuseful
	pub fn reset(&mut self) {
		self.unuseful.clear();
		self.unuseful.extend(self.all.iter().cloned());
		self.idle_for_headers.clear();
		self.idle_for_blocks.clear();
		self.headers_requests.clear();
		self.blocks_requests.clear();
	}

	/// Reset peer tasks && move peer to idle state
	pub fn reset_blocks_tasks(&mut self, peer_index: PeerIndex) -> Vec<H256> {
		self.idle_for_blocks.insert(peer_index);
		self.blocks_requests.remove(&peer_index)
			.map(|mut br| br.blocks.drain().collect())
			.unwrap_or_default()
	}
}

impl HeadersRequest {
	pub fn new() -> Self {
		HeadersRequest {
			timestamp: precise_time_s(),
		}
	}
}

impl BlocksRequest {
	pub fn new() -> Self {
		BlocksRequest {
			timestamp: precise_time_s(),
			blocks: HashSet::new(),
		}
	}
}

impl PeerStats {
	pub fn new() -> Self {
		PeerStats {
			failures: 0,
			speed: AverageSpeedMeter::with_inspect_items(BLOCKS_TO_INSPECT),
			trust: TrustLevel::Suspicious,
		}
	}

	pub fn trust(&self) -> TrustLevel {
		self.trust
	}
}

impl fmt::Debug for Information {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		write!(f, "{} (act: {}, idl: {}, bad: {})", self.all, self.active, self.idle, self.unuseful)
	}
}

#[cfg(test)]
mod tests {
	use primitives::hash::H256;
	use super::{PeersTasks, MAX_PEER_FAILURES, MAX_BLOCKS_FAILURES};
	use types::PeerIndex;

	#[test]
	fn peers_empty_on_start() {
		let peers = PeersTasks::default();
		assert_eq!(peers.idle_peers_for_blocks().len(), 0);
		assert_eq!(peers.idle_peers_for_headers().len(), 0);

		let info = peers.information();
		assert_eq!(info.idle, 0);
		assert_eq!(info.active, 0);
	}

	#[test]
	fn peers_all_unuseful_after_reset() {
		let mut peers = PeersTasks::default();
		peers.on_blocks_requested(7, &vec![H256::default()]);
		peers.on_blocks_requested(8, &vec![H256::default()]);
		assert_eq!(peers.information().idle, 0);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 2);
		peers.reset();
		assert_eq!(peers.information().idle, 0);
		assert_eq!(peers.information().unuseful, 2);
		assert_eq!(peers.information().active, 0);
	}

	#[test]
	fn peer_idle_after_reset_tasks() {
		let mut peers = PeersTasks::default();
		peers.on_blocks_requested(7, &vec![H256::default()]);
		assert_eq!(peers.information().idle, 0);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 1);
		assert_eq!(peers.reset_blocks_tasks(7), vec![H256::default()]);
		assert_eq!(peers.information().idle, 1);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 0);
	}

	#[test]
	fn peers_active_after_headers_request() {
		let mut peers = PeersTasks::default();
		peers.useful_peer(5);
		peers.useful_peer(7);
		assert_eq!(peers.information().idle, 2);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 0);
		peers.on_headers_requested(5);
		assert_eq!(peers.information().idle, 1);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 1);
	}

	#[test]
	fn peers_insert_remove_idle() {
		let mut peers = PeersTasks::default();

		peers.useful_peer(0);
		assert_eq!(peers.information().idle, 1);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 0);
		assert_eq!(peers.idle_peers_for_blocks().len(), 1);
		assert!(peers.idle_peers_for_blocks().contains(&0));

		peers.useful_peer(5);
		assert_eq!(peers.information().idle, 2);
		assert_eq!(peers.information().active, 0);
		let idle_peers: Vec<_> = peers.idle_peers_for_blocks().iter().cloned().collect();
		assert!(idle_peers[0] == 0 || idle_peers[0] == 5);
		assert!(idle_peers[1] == 0 || idle_peers[1] == 5);

		peers.disconnect(7);
		assert_eq!(peers.information().idle, 2);
		assert_eq!(peers.information().active, 0);
		let idle_peers: Vec<_> = peers.idle_peers_for_blocks().iter().cloned().collect();
		assert!(idle_peers[0] == 0 || idle_peers[0] == 5);
		assert!(idle_peers[1] == 0 || idle_peers[1] == 5);

		peers.disconnect(0);
		assert_eq!(peers.information().idle, 1);
		assert_eq!(peers.information().active, 0);
		assert_eq!(peers.idle_peers_for_blocks().len(), 1);
		assert!(peers.idle_peers_for_blocks().contains(&5));
	}

	#[test]
	fn peers_request_blocks() {
		let mut peers = PeersTasks::default();

		peers.useful_peer(5);

		peers.on_blocks_requested(7, &vec![H256::default()]);
		assert_eq!(peers.information().idle, 1);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 1);

		peers.on_blocks_requested(8, &vec![H256::default()]);
		assert_eq!(peers.information().idle, 1);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 2);

		peers.on_block_received(7, &H256::default());
		assert_eq!(peers.information().idle, 2);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 1);

		peers.on_block_received(9, &H256::default());
		assert_eq!(peers.information().idle, 2);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 1);

		peers.on_block_received(8, &"000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f".into());
		assert_eq!(peers.information().idle, 2);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 1);

		peers.on_block_received(8, &H256::default());
		assert_eq!(peers.information().idle, 3);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 0);
	}

	#[test]
	fn peers_worst() {
		let mut peers = PeersTasks::default();

		peers.useful_peer(1);
		peers.useful_peer(2);
		assert_eq!(peers.ordered_blocks_requests().len(), 0);

		peers.on_blocks_requested(1, &vec![H256::default()]);
		assert_eq!(peers.ordered_blocks_requests().len(), 1);
		assert_eq!(*peers.ordered_blocks_requests().keys().nth(0).unwrap(), 1);

		peers.on_blocks_requested(2, &vec![H256::default()]);
		assert_eq!(peers.ordered_blocks_requests().len(), 2);
		assert_eq!(*peers.ordered_blocks_requests().keys().nth(0).unwrap(), 1);
		assert_eq!(*peers.ordered_blocks_requests().keys().nth(1).unwrap(), 2);

		assert_eq!(peers.information().idle, 0);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 2);

		peers.reset_blocks_tasks(1);

		assert_eq!(peers.information().idle, 1);
		assert_eq!(peers.information().unuseful, 0);
		assert_eq!(peers.information().active, 1);

		assert_eq!(peers.ordered_blocks_requests().len(), 1);
		assert_eq!(*peers.ordered_blocks_requests().keys().nth(0).unwrap(), 2);

		for _ in 0..(MAX_PEER_FAILURES + 1) {
			if peers.on_peer_block_failure(2) {
				peers.reset_blocks_tasks(2);
				peers.unuseful_peer(2);
			}
		}

		assert_eq!(peers.ordered_blocks_requests().len(), 0);
		assert_eq!(peers.information().idle, 1);
		assert_eq!(peers.information().unuseful, 1);
		assert_eq!(peers.information().active, 0);
	}

	#[test]
	fn peer_not_inserted_when_known() {
		let mut peers = PeersTasks::default();
		peers.useful_peer(1);
		peers.useful_peer(1);
		assert_eq!(peers.information().active + peers.information().idle + peers.information().unuseful, 1);
		peers.on_blocks_requested(1, &vec![H256::default()]);
		peers.useful_peer(1);
		assert_eq!(peers.information().active + peers.information().idle + peers.information().unuseful, 1);
		for _ in 0..MAX_PEER_FAILURES {
			if peers.on_peer_block_failure(1) {
				peers.reset_blocks_tasks(1);
				peers.unuseful_peer(1);
			}
		}
		peers.useful_peer(1);
		assert_eq!(peers.information().active + peers.information().idle + peers.information().unuseful, 1);
	}

	#[test]
	fn peer_block_failures() {
		let mut peers = PeersTasks::default();
		peers.useful_peer(1);
		peers.on_blocks_requested(1, &vec![H256::from(1)]);
		for _ in 0..MAX_BLOCKS_FAILURES {
			let requested_blocks = peers.reset_blocks_tasks(1);
			let (blocks_to_request, blocks_to_forget) = peers.on_blocks_failure(requested_blocks);
			assert_eq!(blocks_to_request, vec![H256::from(1)]);
			assert_eq!(blocks_to_forget, vec![]);
			peers.on_blocks_requested(1, &vec![H256::from(1)]);
		}
		let requested_blocks = peers.reset_blocks_tasks(1);
		let (blocks_to_request, blocks_to_forget) = peers.on_blocks_failure(requested_blocks);
		assert_eq!(blocks_to_request, vec![]);
		assert_eq!(blocks_to_forget, vec![H256::from(1)]);
	}

	#[test]
	fn peer_sort_peers_for_blocks() {
		let mut peers = PeersTasks::default();
		peers.on_blocks_requested(1, &vec![H256::from(1), H256::from(2)]);
		peers.on_blocks_requested(2, &vec![H256::from(3), H256::from(4)]);
		peers.on_block_received(2, &H256::from(3));
		peers.on_block_received(2, &H256::from(4));

		use std::thread;
		use std::time::Duration;
		thread::park_timeout(Duration::from_millis(50));

		peers.on_block_received(1, &H256::from(1));
		peers.on_block_received(1, &H256::from(2));

		let mut peers_for_blocks: Vec<PeerIndex> = vec![1, 2];
		peers.sort_peers_for_blocks(&mut peers_for_blocks);
		assert_eq!(peers_for_blocks[0], 2);
		assert_eq!(peers_for_blocks[1], 1);
	}
}