Collate network PoW computes into a fixed-sized pool, with dead peer detection.

Also added Named/DaemonThreadFactory classes.

Network EPC now uses NamedThreadFactory for easier debugging.

Added settings field "networkPoWComputePoolSize", default 2, which
seems to work with both low-power ARM boards and high-power desktops.

src/main/java/org/qortal/network/Handshake.java

@@ -1,6 +1,8 @@
 package org.qortal.network;
 
 import java.util.Arrays;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -13,7 +15,9 @@ import org.qortal.network.message.ChallengeMessage;
 import org.qortal.network.message.HelloMessage;
 import org.qortal.network.message.Message;
 import org.qortal.network.message.Message.MessageType;
+import org.qortal.settings.Settings;
 import org.qortal.network.message.ResponseMessage;
+import org.qortal.utils.DaemonThreadFactory;
 import org.qortal.utils.NTP;
 
 import com.google.common.primitives.Bytes;
@@ -27,6 +31,7 @@ public enum Handshake {
 
 		@Override
 		public void action(Peer peer) {
+			/* Never called */
 		}
 	},
 	HELLO(MessageType.HELLO) {
@@ -183,7 +188,12 @@ public enum Handshake {
 			final byte[] data = Crypto.digest(Bytes.concat(sharedSecret, peersChallenge));
 
 			// We do this in a new thread as it can take a while...
-			Thread responseThread = new Thread(() -> {
+			responseExecutor.execute(() -> {
+				// Are we still connected?
+				if (peer.isStopping())
+					// No point computing for dead peer
+					return;
+
 				Integer nonce = MemoryPoW.compute2(data, POW_BUFFER_SIZE, POW_DIFFICULTY);
 
 				Message responseMessage = new ResponseMessage(nonce, data);
@@ -197,9 +207,6 @@ public enum Handshake {
 					Network.getInstance().onHandshakeCompleted(peer);
 				}
 			});
-
-			responseThread.setDaemon(true);
-			responseThread.start();
 		}
 	},
 	// Interim holding state while we compute RESPONSE to send to inbound peer
@@ -237,6 +244,7 @@ public enum Handshake {
 
 	private static final int POW_BUFFER_SIZE = 8 * 1024 * 1024; // bytes
 	private static final int POW_DIFFICULTY = 8; // leading zero bits
+	private static final ExecutorService responseExecutor = Executors.newFixedThreadPool(Settings.getInstance().getNetworkPoWComputePoolSize(), new DaemonThreadFactory("Network-PoW"));
 
 	private static final byte[] ZERO_CHALLENGE = new byte[ChallengeMessage.CHALLENGE_LENGTH];
 

src/main/java/org/qortal/network/Network.java

@@ -55,6 +55,7 @@ import org.qortal.utils.ExecuteProduceConsume;
 // import org.qortal.utils.ExecutorDumper;
 import org.qortal.utils.ExecuteProduceConsume.StatsSnapshot;
 import org.qortal.utils.NTP;
+import org.qortal.utils.NamedThreadFactory;
 
 // For managing peers
 public class Network {
@@ -151,7 +152,8 @@ public class Network {
 		ExecutorService networkExecutor = new ThreadPoolExecutor(1,
 				Settings.getInstance().getMaxNetworkThreadPoolSize(),
 				NETWORK_EPC_KEEPALIVE, TimeUnit.SECONDS,
-				new SynchronousQueue<Runnable>());
+				new SynchronousQueue<Runnable>(),
+				new NamedThreadFactory("Network-EPC"));
 		networkEPC = new NetworkProcessor(networkExecutor);
 	}
 
@@ -355,7 +357,7 @@ public class Network {
 
 		private Task maybeProducePeerPingTask(Long now) {
 			// Ask connected peers whether they need a ping
-			for (Peer peer : getConnectedPeers()) {
+			for (Peer peer : getHandshakedPeers()) {
 				Task peerTask = peer.getPingTask(now);
 				if (peerTask != null)
 					return peerTask;

src/main/java/org/qortal/settings/Settings.java

@@ -92,6 +92,8 @@ public class Settings {
 	private int maxPeers = 32;
 	/** Maximum number of threads for network engine. */
 	private int maxNetworkThreadPoolSize = 20;
+	/** Maximum number of threads for network proof-of-work compute, used during handshaking. */
+	private int networkPoWComputePoolSize = 2;
 
 	// Which blockchains this node is running
 	private String blockchainConfig = null; // use default from resources
@@ -355,6 +357,10 @@ public class Settings {
 		return this.maxNetworkThreadPoolSize;
 	}
 
+	public int getNetworkPoWComputePoolSize() {
+		return this.networkPoWComputePoolSize;
+	}
+
 	public String getBlockchainConfig() {
 		return this.blockchainConfig;
 	}

src/main/java/org/qortal/utils/DaemonThreadFactory.java

@@ -0,0 +1,31 @@
+package org.qortal.utils;
+
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class DaemonThreadFactory implements ThreadFactory {
+
+	private final String name;
+	private final AtomicInteger threadNumber = new AtomicInteger(1);
+
+	public DaemonThreadFactory(String name) {
+		this.name = name;
+	}
+
+	public DaemonThreadFactory() {
+		this(null);
+	}
+
+	@Override
+	public Thread newThread(Runnable runnable) {
+		Thread thread = Executors.defaultThreadFactory().newThread(runnable);
+		thread.setDaemon(true);
+
+		if (this.name != null)
+			thread.setName(this.name + "-" + this.threadNumber.getAndIncrement());
+
+		return thread;
+	}
+
+}

src/main/java/org/qortal/utils/NamedThreadFactory.java

@@ -0,0 +1,24 @@
+package org.qortal.utils;
+
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class NamedThreadFactory implements ThreadFactory {
+
+	private final String name;
+	private final AtomicInteger threadNumber = new AtomicInteger(1);
+
+	public NamedThreadFactory(String name) {
+		this.name = name;
+	}
+
+	@Override
+	public Thread newThread(Runnable runnable) {
+		Thread thread = Executors.defaultThreadFactory().newThread(runnable);
+		thread.setName(this.name + "-" + this.threadNumber.getAndIncrement());
+
+		return thread;
+	}
+
+}