Introduce options for fine-grained management of work queue. (#1484)

* Introduce options for fine-grained management of work queue.

- Minimum reseal period between non-mandatory (transaction) reseals.
- Maximum historical cached block size.

Defaults changed to reflect real-world scenarios (2s, 20 blocks).

* Fix test bug.

* 50 -> 20.

parity/cli.rs

@@ -137,6 +137,13 @@ Sealing/Mining Options:
                            own - reseal only on a new local transaction;
                            ext - reseal only on a new external transaction;
                            all - reseal on all new transactions [default: all].
+  --reseal-min-period MS   Specify the minimum time between reseals from 
+                           incoming transactions. MS is time measured in
+                           milliseconds [default: 2000].
+  --work-queue-size ITEMS  Specify the number of historical work packages
+                           which are kept cached lest a solution is found for 
+                           them later. High values take more memory but result
+                           in fewer unusable solutions [default: 20].
   --tx-gas-limit GAS       Apply a limit of GAS as the maximum amount of gas
                            a single transaction may have for it to be mined.
   --relay-set SET          Set of transactions to relay. SET may be:
@@ -302,6 +309,8 @@ pub struct Args {
 	pub flag_no_token: bool,
 	pub flag_force_sealing: bool,
 	pub flag_reseal_on_txs: String,
+	pub flag_reseal_min_period: u64,
+	pub flag_work_queue_size: usize,
 	pub flag_tx_gas_limit: Option<String>,
 	pub flag_relay_set: String,
 	pub flag_author: Option<String>,

parity/configuration.rs

@@ -16,6 +16,7 @@
 
 use std::env;
 use std::fs::File;
+use std::time::Duration;
 use std::io::{BufRead, BufReader};
 use std::net::{SocketAddr, IpAddr};
 use std::path::PathBuf;
@@ -103,6 +104,8 @@ impl Configuration {
 				"lenient" => PendingSet::SealingOrElseQueue,
 				x => die!("{}: Invalid value for --relay-set option. Use --help for more information.", x)
 			},
+			reseal_min_period: Duration::from_millis(self.args.flag_reseal_min_period),
+			work_queue_size: self.args.flag_work_queue_size,
 		}
 	}