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    // Copyright 2015-2017 Parity Technologies (UK) Ltd.
    // This file is part of Parity.

    // Parity is free software: you can redistribute it and/or modify
    // it under the terms of the GNU General Public License as published by
    // the Free Software Foundation, either version 3 of the License, or
    // (at your option) any later version.

    // Parity 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 General Public License for more details.

    // You should have received a copy of the GNU General Public License
    // along with Parity.  If not, see <http://www.gnu.org/licenses/>.

    //! A queue of blocks. Sits between network or other I/O and the `BlockChain`.
    //! Sorts them ready for blockchain insertion.

    use std::thread::{self, JoinHandle};
    use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering as AtomicOrdering};
    use std::sync::{Condvar as SCondvar, Mutex as SMutex};
    use util::*;
    use io::*;
    use error::*;
    use engines::Engine;
    use service::*;

    use self::kind::{BlockLike, Kind};

    pub use types::verification_queue_info::VerificationQueueInfo as QueueInfo;

    pub mod kind;

    const MIN_MEM_LIMIT: usize = 16384;
    const MIN_QUEUE_LIMIT: usize = 512;

    // maximum possible number of verification threads.
    const MAX_VERIFIERS: usize = 8;

    /// Type alias for block queue convenience.
    pub type BlockQueue = VerificationQueue<self::kind::Blocks>;

    /// Type alias for header queue convenience.
    pub type HeaderQueue = VerificationQueue<self::kind::Headers>;

    /// Verification queue configuration
    #[derive(Debug, PartialEq, Clone)]
    pub struct Config {
    	/// Maximum number of items to keep in unverified queue.
    	/// When the limit is reached, is_full returns true.
    	pub max_queue_size: usize,
    	/// Maximum heap memory to use.
    	/// When the limit is reached, is_full returns true.
    	pub max_mem_use: usize,
    	/// Settings for the number of verifiers and adaptation strategy.
    	pub verifier_settings: VerifierSettings,
    }

    impl Default for Config {
    	fn default() -> Self {
    		Config {
    			max_queue_size: 30000,
    			max_mem_use: 50 * 1024 * 1024,
    			verifier_settings: VerifierSettings::default(),
    		}
    	}
    }

    /// Verifier settings.
    #[derive(Debug, PartialEq, Clone)]
    pub struct VerifierSettings {
    	/// Whether to scale amount of verifiers according to load.
    	// Todo: replace w/ strategy enum?
    	pub scale_verifiers: bool,
    	/// Beginning amount of verifiers.
    	pub num_verifiers: usize,
    }

    impl Default for VerifierSettings {
    	fn default() -> Self {
    		VerifierSettings {
    			scale_verifiers: false,
    			num_verifiers: MAX_VERIFIERS,
    		}
    	}
    }

    // pool states
    enum State {
    	// all threads with id < inner value are to work.
    	Work(usize),
    	Exit,
    }

    /// An item which is in the process of being verified.
    pub struct Verifying<K: Kind> {
    	hash: H256,
    	output: Option<K::Verified>,
    }

    impl<K: Kind> HeapSizeOf for Verifying<K> {
    	fn heap_size_of_children(&self) -> usize {
    		self.output.heap_size_of_children()
    	}
    }

    /// Status of items in the queue.
    pub enum Status {
    	/// Currently queued.
    	Queued,
    	/// Known to be bad.
    	Bad,
    	/// Unknown.
    	Unknown,
    }

    // the internal queue sizes.
    struct Sizes {
    	unverified: AtomicUsize,
    	verifying: AtomicUsize,
    	verified: AtomicUsize,
    }

    /// A queue of items to be verified. Sits between network or other I/O and the `BlockChain`.
    /// Keeps them in the same order as inserted, minus invalid items.
    pub struct VerificationQueue<K: Kind> {
    	panic_handler: Arc<PanicHandler>,
    	engine: Arc<Engine>,
    	more_to_verify: Arc<SCondvar>,
    	verification: Arc<Verification<K>>,
    	deleting: Arc<AtomicBool>,
    	ready_signal: Arc<QueueSignal>,
    	empty: Arc<SCondvar>,
    	processing: RwLock<HashMap<H256, U256>>, // hash to difficulty
    	ticks_since_adjustment: AtomicUsize,
    	max_queue_size: usize,
    	max_mem_use: usize,
    	scale_verifiers: bool,
    	verifier_handles: Vec<JoinHandle<()>>,
    	state: Arc<(Mutex<State>, Condvar)>,
    	total_difficulty: RwLock<U256>,
    }

    struct QueueSignal {
    	deleting: Arc<AtomicBool>,
    	signalled: AtomicBool,
    	message_channel: Mutex<IoChannel<ClientIoMessage>>,
    }

    impl QueueSignal {
    	#[cfg_attr(feature="dev", allow(bool_comparison))]
    	fn set_sync(&self) {
    		// Do not signal when we are about to close
    		if self.deleting.load(AtomicOrdering::Relaxed) {
    			return;
    		}

    		if self.signalled.compare_and_swap(false, true, AtomicOrdering::Relaxed) == false {
    			let channel = self.message_channel.lock().clone();
    			if let Err(e) = channel.send_sync(ClientIoMessage::BlockVerified) {
    				debug!("Error sending BlockVerified message: {:?}", e);
    			}
    		}
    	}

    	#[cfg_attr(feature="dev", allow(bool_comparison))]
    	fn set_async(&self) {
    		// Do not signal when we are about to close
    		if self.deleting.load(AtomicOrdering::Relaxed) {
    			return;
    		}

    		if self.signalled.compare_and_swap(false, true, AtomicOrdering::Relaxed) == false {
    			let channel = self.message_channel.lock().clone();
    			if let Err(e) = channel.send(ClientIoMessage::BlockVerified) {
    				debug!("Error sending BlockVerified message: {:?}", e);
    			}
    		}
    	}

    	fn reset(&self) {
    		self.signalled.store(false, AtomicOrdering::Relaxed);
    	}
    }

    struct Verification<K: Kind> {
    	// All locks must be captured in the order declared here.
    	unverified: Mutex<VecDeque<K::Unverified>>,
    	verifying: Mutex<VecDeque<Verifying<K>>>,
    	verified: Mutex<VecDeque<K::Verified>>,
    	bad: Mutex<HashSet<H256>>,
    	more_to_verify: SMutex<()>,
    	empty: SMutex<()>,
    	sizes: Sizes,
    	check_seal: bool,
    }

    impl<K: Kind> VerificationQueue<K> {
    	/// Creates a new queue instance.
    	pub fn new(config: Config, engine: Arc<Engine>, message_channel: IoChannel<ClientIoMessage>, check_seal: bool) -> Self {
    		let verification = Arc::new(Verification {
    			unverified: Mutex::new(VecDeque::new()),
    			verifying: Mutex::new(VecDeque::new()),
    			verified: Mutex::new(VecDeque::new()),
    			bad: Mutex::new(HashSet::new()),
    			more_to_verify: SMutex::new(()),
    			empty: SMutex::new(()),
    			sizes: Sizes {
    				unverified: AtomicUsize::new(0),
    				verifying: AtomicUsize::new(0),
    				verified: AtomicUsize::new(0),
    			},
    			check_seal: check_seal,
    		});
    		let more_to_verify = Arc::new(SCondvar::new());
    		let deleting = Arc::new(AtomicBool::new(false));
    		let ready_signal = Arc::new(QueueSignal {
    			deleting: deleting.clone(),
    			signalled: AtomicBool::new(false),
    			message_channel: Mutex::new(message_channel),
    		});
    		let empty = Arc::new(SCondvar::new());
    		let panic_handler = PanicHandler::new_in_arc();
    		let scale_verifiers = config.verifier_settings.scale_verifiers;

    		let num_cpus = ::num_cpus::get();
    		let max_verifiers = min(num_cpus, MAX_VERIFIERS);
    		let default_amount = max(1, min(max_verifiers, config.verifier_settings.num_verifiers));
    		let state = Arc::new((Mutex::new(State::Work(default_amount)), Condvar::new()));
    		let mut verifier_handles = Vec::with_capacity(max_verifiers);

    		debug!(target: "verification", "Allocating {} verifiers, {} initially active", max_verifiers, default_amount);
    		debug!(target: "verification", "Verifier auto-scaling {}", if scale_verifiers { "enabled" } else { "disabled" });

    		for i in 0..max_verifiers {
    			debug!(target: "verification", "Adding verification thread #{}", i);

    			let panic_handler = panic_handler.clone();
    			let verification = verification.clone();
    			let engine = engine.clone();
    			let wait = more_to_verify.clone();
    			let ready = ready_signal.clone();
    			let empty = empty.clone();
    			let state = state.clone();

    			let handle = thread::Builder::new()
    				.name(format!("Verifier #{}", i))
    				.spawn(move || {
    					panic_handler.catch_panic(move || {
    						VerificationQueue::verify(
    							verification,
    							engine,
    							wait,
    							ready,
    							empty,
    							state,
    							i,
    						)
    					}).unwrap()
    				})
    				.expect("Failed to create verifier thread.");
    			verifier_handles.push(handle);
    		}

    		VerificationQueue {
    			engine: engine,
    			panic_handler: panic_handler,
    			ready_signal: ready_signal,
    			more_to_verify: more_to_verify,
    			verification: verification,
    			deleting: deleting,
    			processing: RwLock::new(HashMap::new()),
    			empty: empty,
    			ticks_since_adjustment: AtomicUsize::new(0),
    			max_queue_size: max(config.max_queue_size, MIN_QUEUE_LIMIT),
    			max_mem_use: max(config.max_mem_use, MIN_MEM_LIMIT),
    			scale_verifiers: scale_verifiers,
    			verifier_handles: verifier_handles,
    			state: state,
    			total_difficulty: RwLock::new(0.into()),
    		}
    	}

    	fn verify(
    		verification: Arc<Verification<K>>,
    		engine: Arc<Engine>,
    		wait: Arc<SCondvar>,
    		ready: Arc<QueueSignal>,
    		empty: Arc<SCondvar>,
    		state: Arc<(Mutex<State>, Condvar)>,
    		id: usize,
    	) {
    		loop {
    			// check current state.
    			{
    				let mut cur_state = state.0.lock();
    				while let State::Work(x) = *cur_state {
    					// sleep until this thread is required.
    					if id < x { break }

    					debug!(target: "verification", "verifier {} sleeping", id);
    					state.1.wait(&mut cur_state);
    					debug!(target: "verification", "verifier {} waking up", id);
    				}

    				if let State::Exit = *cur_state {
    					debug!(target: "verification", "verifier {} exiting", id);
    					break;
    				}
    			}

    			// wait for work if empty.
    			{
    				let mut more_to_verify = verification.more_to_verify.lock().unwrap();

    				if verification.unverified.lock().is_empty() && verification.verifying.lock().is_empty() {
    					empty.notify_all();
    				}

    				while verification.unverified.lock().is_empty() {
    					if let State::Exit = *state.0.lock() {
    						debug!(target: "verification", "verifier {} exiting", id);
    						return;
    					}

    					more_to_verify = wait.wait(more_to_verify).unwrap();
    				}

    				if let State::Exit = *state.0.lock() {
    					debug!(target: "verification", "verifier {} exiting", id);
    					return;
    				}
    			}

    			// do work.
    			let item = {
    				// acquire these locks before getting the item to verify.
    				let mut unverified = verification.unverified.lock();
    				let mut verifying = verification.verifying.lock();

    				let item = match unverified.pop_front() {
    					Some(item) => item,
    					None => continue,
    				};

    				verification.sizes.unverified.fetch_sub(item.heap_size_of_children(), AtomicOrdering::SeqCst);
    				verifying.push_back(Verifying { hash: item.hash(), output: None });
    				item
    			};

    			let hash = item.hash();
    			let is_ready = match K::verify(item, &*engine, verification.check_seal) {
    				Ok(verified) => {
    					let mut verifying = verification.verifying.lock();
    					let mut idx = None;
    					for (i, e) in verifying.iter_mut().enumerate() {
    						if e.hash == hash {
    							idx = Some(i);

    							verification.sizes.verifying.fetch_add(verified.heap_size_of_children(), AtomicOrdering::SeqCst);
    							e.output = Some(verified);
    							break;
    						}
    					}

    					if idx == Some(0) {
    						// we're next!
    						let mut verified = verification.verified.lock();
    						let mut bad = verification.bad.lock();
    						VerificationQueue::drain_verifying(&mut verifying, &mut verified, &mut bad, &verification.sizes);
    						true
    					} else {
    						false
    					}
    				},
    				Err(_) => {
    					let mut verifying = verification.verifying.lock();
    					let mut verified = verification.verified.lock();
    					let mut bad = verification.bad.lock();

    					bad.insert(hash.clone());
    					verifying.retain(|e| e.hash != hash);

    					if verifying.front().map_or(false, |x| x.output.is_some()) {
    						VerificationQueue::drain_verifying(&mut verifying, &mut verified, &mut bad, &verification.sizes);
    						true
    					} else {
    						false
    					}
    				}
    			};
    			if is_ready {
    				// Import the block immediately
    				ready.set_sync();
    			}
    		}
    	}

    	fn drain_verifying(
    		verifying: &mut VecDeque<Verifying<K>>,
    		verified: &mut VecDeque<K::Verified>,
    		bad: &mut HashSet<H256>,
    		sizes: &Sizes,
    	) {
    		let mut removed_size = 0;
    		let mut inserted_size = 0;

    		while let Some(output) = verifying.front_mut().and_then(|x| x.output.take()) {
    			assert!(verifying.pop_front().is_some());
    			let size = output.heap_size_of_children();
    			removed_size += size;

    			if bad.contains(&output.parent_hash()) {
    				bad.insert(output.hash());
    			} else {
    				inserted_size += size;
    				verified.push_back(output);
    			}
    		}

    		sizes.verifying.fetch_sub(removed_size, AtomicOrdering::SeqCst);
    		sizes.verified.fetch_add(inserted_size, AtomicOrdering::SeqCst);
    	}

    	/// Clear the queue and stop verification activity.
    	pub fn clear(&self) {
    		let mut unverified = self.verification.unverified.lock();
    		let mut verifying = self.verification.verifying.lock();
    		let mut verified = self.verification.verified.lock();
    		unverified.clear();
    		verifying.clear();
    		verified.clear();

    		let sizes = &self.verification.sizes;
    		sizes.unverified.store(0, AtomicOrdering::Release);
    		sizes.verifying.store(0, AtomicOrdering::Release);
    		sizes.verified.store(0, AtomicOrdering::Release);
    		*self.total_difficulty.write() = 0.into();

    		self.processing.write().clear();
    	}

    	/// Wait for unverified queue to be empty
    	pub fn flush(&self) {
    		let mut lock = self.verification.empty.lock().unwrap();
    		while !self.verification.unverified.lock().is_empty() || !self.verification.verifying.lock().is_empty() {
    			lock = self.empty.wait(lock).unwrap();
    		}
    	}

    	/// Check if the item is currently in the queue
    	pub fn status(&self, hash: &H256) -> Status {
    		if self.processing.read().contains_key(hash) {
    			return Status::Queued;
    		}
    		if self.verification.bad.lock().contains(hash) {
    			return Status::Bad;
    		}
    		Status::Unknown
    	}

    	/// Add a block to the queue.
    	pub fn import(&self, input: K::Input) -> ImportResult {
    		let h = input.hash();
    		{
    			if self.processing.read().contains_key(&h) {
    				return Err(ImportError::AlreadyQueued.into());
    			}

    			let mut bad = self.verification.bad.lock();
    			if bad.contains(&h) {
    				return Err(ImportError::KnownBad.into());
    			}

    			if bad.contains(&input.parent_hash()) {
    				bad.insert(h.clone());
    				return Err(ImportError::KnownBad.into());
    			}
    		}

    		match K::create(input, &*self.engine) {
    			Ok(item) => {
    				self.verification.sizes.unverified.fetch_add(item.heap_size_of_children(), AtomicOrdering::SeqCst);

    				self.processing.write().insert(h.clone(), item.difficulty());
    				{
    					let mut td = self.total_difficulty.write();
    					*td = *td + item.difficulty();
    				}
    				self.verification.unverified.lock().push_back(item);
    				self.more_to_verify.notify_all();
    				Ok(h)
    			},
    			Err(err) => {
    				match err {
    					// Don't mark future blocks as bad.
    					Error::Block(BlockError::InvalidTimestamp(ref e)) if e.max.is_some() => {},
    					_ => {
    						self.verification.bad.lock().insert(h.clone());
    					}
    				}
    				Err(err)
    			}
    		}
    	}

    	/// Mark given item and all its children as bad. pauses verification
    	/// until complete.
    	pub fn mark_as_bad(&self, hashes: &[H256]) {
    		if hashes.is_empty() {
    			return;
    		}
    		let mut verified_lock = self.verification.verified.lock();
    		let mut verified = &mut *verified_lock;
    		let mut bad = self.verification.bad.lock();
    		let mut processing = self.processing.write();
    		bad.reserve(hashes.len());
    		for hash in hashes {
    			bad.insert(hash.clone());
    			if let Some(difficulty) = processing.remove(hash) {
    				let mut td = self.total_difficulty.write();
    				*td = *td - difficulty;
    			}
    		}

    		let mut new_verified = VecDeque::new();
    		let mut removed_size = 0;
    		for output in verified.drain(..) {
    			if bad.contains(&output.parent_hash()) {
    				removed_size += output.heap_size_of_children();
    				bad.insert(output.hash());
    				if let Some(difficulty) = processing.remove(&output.hash()) {
    					let mut td = self.total_difficulty.write();
    					*td = *td - difficulty;
    				}
    			} else {
    				new_verified.push_back(output);
    			}
    		}

    		self.verification.sizes.verified.fetch_sub(removed_size, AtomicOrdering::SeqCst);
    		*verified = new_verified;
    	}

    	/// Mark given item as processed.
    	/// Returns true if the queue becomes empty.
    	pub fn mark_as_good(&self, hashes: &[H256]) -> bool {
    		if hashes.is_empty() {
    			return self.processing.read().is_empty();
    		}
    		let mut processing = self.processing.write();
    		for hash in hashes {
    			if let Some(difficulty) = processing.remove(hash) {
    				let mut td = self.total_difficulty.write();
    				*td = *td - difficulty;
    			}
    		}
    		processing.is_empty()
    	}

    	/// Removes up to `max` verified items from the queue
    	pub fn drain(&self, max: usize) -> Vec<K::Verified> {
    		let mut verified = self.verification.verified.lock();
    		let count = min(max, verified.len());
    		let result = verified.drain(..count).collect::<Vec<_>>();

    		let drained_size = result.iter().map(HeapSizeOf::heap_size_of_children).fold(0, |a, c| a + c);
    		self.verification.sizes.verified.fetch_sub(drained_size, AtomicOrdering::SeqCst);

    		self.ready_signal.reset();
    		if !verified.is_empty() {
    			self.ready_signal.set_async();
    		}
    		result
    	}

    	/// Get queue status.
    	pub fn queue_info(&self) -> QueueInfo {
    		use std::mem::size_of;

    		let (unverified_len, unverified_bytes) = {
    			let len = self.verification.unverified.lock().len();
    			let size = self.verification.sizes.unverified.load(AtomicOrdering::Acquire);

    			(len, size + len * size_of::<K::Unverified>())
    		};
    		let (verifying_len, verifying_bytes) = {
    			let len = self.verification.verifying.lock().len();
    			let size = self.verification.sizes.verifying.load(AtomicOrdering::Acquire);
    			(len, size + len * size_of::<Verifying<K>>())
    		};
    		let (verified_len, verified_bytes) = {
    			let len = self.verification.verified.lock().len();
    			let size = self.verification.sizes.verified.load(AtomicOrdering::Acquire);
    			(len, size + len * size_of::<K::Verified>())
    		};

    		QueueInfo {
    			unverified_queue_size: unverified_len,
    			verifying_queue_size: verifying_len,
    			verified_queue_size: verified_len,
    			max_queue_size: self.max_queue_size,
    			max_mem_use: self.max_mem_use,
    			mem_used: unverified_bytes
    					   + verifying_bytes
    					   + verified_bytes
    		}
    	}

    	/// Get the total difficulty of all the blocks in the queue.
    	pub fn total_difficulty(&self) -> U256 {
    		self.total_difficulty.read().clone()
    	}

    	/// Get the current number of working verifiers.
    	pub fn num_verifiers(&self) -> usize {
    		match *self.state.0.lock() {
    			State::Work(x) => x,
    			State::Exit => panic!("state only set to exit on drop; queue live now; qed"),
    		}
    	}

    	/// Optimise memory footprint of the heap fields, and adjust the number of threads
    	/// to better suit the workload.
    	pub fn collect_garbage(&self) {
    		// number of ticks to average queue stats over
    		// when deciding whether to change the number of verifiers.
    		#[cfg(not(test))]
    		const READJUSTMENT_PERIOD: usize = 12;

    		#[cfg(test)]
    		const READJUSTMENT_PERIOD: usize = 1;

    		let (u_len, v_len) = {
    			let u_len = {
    				let mut q = self.verification.unverified.lock();
    				q.shrink_to_fit();
    				q.len()
    			};
    			self.verification.verifying.lock().shrink_to_fit();

    			let v_len = {
    				let mut q = self.verification.verified.lock();
    				q.shrink_to_fit();
    				q.len()
    			};

    			(u_len as isize, v_len as isize)
    		};

    		self.processing.write().shrink_to_fit();

    		if !self.scale_verifiers { return }

    		if self.ticks_since_adjustment.fetch_add(1, AtomicOrdering::SeqCst) + 1 >= READJUSTMENT_PERIOD {
    			self.ticks_since_adjustment.store(0, AtomicOrdering::SeqCst);
    		} else {
    			return;
    		}

    		let current = self.num_verifiers();

    		let diff = (v_len - u_len).abs();
    		let total = v_len + u_len;

    		self.scale_verifiers(
    			if u_len < 20 {
    				1
    			} else if diff <= total / 10 {
    				current
    			} else if v_len > u_len {
    				current - 1
    			} else {
    				current + 1
    			}
    		);
    	}

    	// wake up or sleep verifiers to get as close to the target as
    	// possible, never going over the amount of initially allocated threads
    	// or below 1.
    	fn scale_verifiers(&self, target: usize) {
    		let current = self.num_verifiers();
    		let target = min(self.verifier_handles.len(), target);
    		let target = max(1, target);

    		debug!(target: "verification", "Scaling from {} to {} verifiers", current, target);

    		*self.state.0.lock() = State::Work(target);
    		self.state.1.notify_all();
    	}
    }

    impl<K: Kind> MayPanic for VerificationQueue<K> {
    	fn on_panic<F>(&self, closure: F) where F: OnPanicListener {
    		self.panic_handler.on_panic(closure);
    	}
    }

    impl<K: Kind> Drop for VerificationQueue<K> {
    	fn drop(&mut self) {
    		trace!(target: "shutdown", "[VerificationQueue] Closing...");
    		self.clear();
    		self.deleting.store(true, AtomicOrdering::SeqCst);

    		// set exit state; should be done before `more_to_verify` notification.
    		*self.state.0.lock() = State::Exit;
    		self.state.1.notify_all();

    		// acquire this lock to force threads to reach the waiting point
    		// if they're in-between the exit check and the more_to_verify wait.
    		{
    			let _more = self.verification.more_to_verify.lock().unwrap();
    			self.more_to_verify.notify_all();
    		}

    		// wait for all verifier threads to join.
    		for thread in self.verifier_handles.drain(..) {
    			thread.join().expect("Propagating verifier thread panic on shutdown");
    		}

    		trace!(target: "shutdown", "[VerificationQueue] Closed.");
    	}
    }

    #[cfg(test)]
    mod tests {
    	use util::*;
    	use io::*;
    	use spec::*;
    	use super::{BlockQueue, Config, State};
    	use super::kind::blocks::Unverified;
    	use tests::helpers::*;
    	use error::*;
    	use views::*;

    	// create a test block queue.
    	// auto_scaling enables verifier adjustment.
    	fn get_test_queue(auto_scale: bool) -> BlockQueue {
    		let spec = get_test_spec();
    		let engine = spec.engine;

    		let mut config = Config::default();
    		config.verifier_settings.scale_verifiers = auto_scale;
    		BlockQueue::new(config, engine, IoChannel::disconnected(), true)
    	}

    	#[test]
    	fn can_be_created() {
    		// TODO better test
    		let spec = Spec::new_test();
    		let engine = spec.engine;
    		let _ = BlockQueue::new(Config::default(), engine, IoChannel::disconnected(), true);
    	}

    	#[test]
    	fn can_import_blocks() {
    		let queue = get_test_queue(false);
    		if let Err(e) = queue.import(Unverified::new(get_good_dummy_block())) {
    			panic!("error importing block that is valid by definition({:?})", e);
    		}
    	}

    	#[test]
    	fn returns_error_for_duplicates() {
    		let queue = get_test_queue(false);
    		if let Err(e) = queue.import(Unverified::new(get_good_dummy_block())) {
    			panic!("error importing block that is valid by definition({:?})", e);
    		}

    		let duplicate_import = queue.import(Unverified::new(get_good_dummy_block()));
    		match duplicate_import {
    			Err(e) => {
    				match e {
    					Error::Import(ImportError::AlreadyQueued) => {},
    					_ => { panic!("must return AlreadyQueued error"); }
    				}
    			}
    			Ok(_) => { panic!("must produce error"); }
    		}
    	}

    	#[test]
    	fn returns_total_difficulty() {
    		let queue = get_test_queue(false);
    		let block = get_good_dummy_block();
    		let hash = BlockView::new(&block).header().hash().clone();
    		if let Err(e) = queue.import(Unverified::new(block)) {
    			panic!("error importing block that is valid by definition({:?})", e);
    		}
    		queue.flush();
    		assert_eq!(queue.total_difficulty(), 131072.into());
    		queue.drain(10);
    		assert_eq!(queue.total_difficulty(), 131072.into());
    		queue.mark_as_good(&[ hash ]);
    		assert_eq!(queue.total_difficulty(), 0.into());
    	}

    	#[test]
    	fn returns_ok_for_drained_duplicates() {
    		let queue = get_test_queue(false);
    		let block = get_good_dummy_block();
    		let hash = BlockView::new(&block).header().hash().clone();
    		if let Err(e) = queue.import(Unverified::new(block)) {
    			panic!("error importing block that is valid by definition({:?})", e);
    		}
    		queue.flush();
    		queue.drain(10);
    		queue.mark_as_good(&[ hash ]);

    		if let Err(e) = queue.import(Unverified::new(get_good_dummy_block())) {
    			panic!("error importing block that has already been drained ({:?})", e);
    		}
    	}

    	#[test]
    	fn returns_empty_once_finished() {
    		let queue = get_test_queue(false);
    		queue.import(Unverified::new(get_good_dummy_block()))
    			.expect("error importing block that is valid by definition");
    		queue.flush();
    		queue.drain(1);

    		assert!(queue.queue_info().is_empty());
    	}

    	#[test]
    	fn test_mem_limit() {
    		let spec = get_test_spec();
    		let engine = spec.engine;
    		let mut config = Config::default();
    		config.max_mem_use = super::MIN_MEM_LIMIT;  // empty queue uses about 15000
    		let queue = BlockQueue::new(config, engine, IoChannel::disconnected(), true);
    		assert!(!queue.queue_info().is_full());
    		let mut blocks = get_good_dummy_block_seq(50);
    		for b in blocks.drain(..) {
    			queue.import(Unverified::new(b)).unwrap();
    		}
    		assert!(queue.queue_info().is_full());
    	}

    	#[test]
    	fn scaling_limits() {
    		use super::MAX_VERIFIERS;

    		let queue = get_test_queue(true);
    		queue.scale_verifiers(MAX_VERIFIERS + 1);

    		assert!(queue.num_verifiers() < MAX_VERIFIERS + 1);

    		queue.scale_verifiers(0);

    		assert!(queue.num_verifiers() == 1);
    	}

    	#[test]
    	fn readjust_verifiers() {
    		let queue = get_test_queue(true);

    		// put all the verifiers to sleep to ensure
    		// the test isn't timing sensitive.
    		*queue.state.0.lock() = State::Work(0);

    		for block in get_good_dummy_block_seq(5000) {
    			queue.import(Unverified::new(block)).expect("Block good by definition; qed");
    		}

    		// almost all unverified == bump verifier count.
    		queue.collect_garbage();
    		assert_eq!(queue.num_verifiers(), 1);

    		queue.flush();

    		// nothing to verify == use minimum number of verifiers.
    		queue.collect_garbage();
    		assert_eq!(queue.num_verifiers(), 1);
    	}
    }

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