Dynamically allocate/deallocate Peer byteBuffer to reduce memory load at the expense of extra GC

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

@@ -61,6 +61,8 @@ public class Peer {
 	private InetSocketAddress resolvedAddress = null;
 	/** True if remote address is loopback/link-local/site-local, false otherwise. */
 	private boolean isLocal;
+
+	private final Object byteBufferLock = new Object();
 	private volatile ByteBuffer byteBuffer;
 	private Map<Integer, BlockingQueue<Message>> replyQueues;
 	private LinkedBlockingQueue<Message> pendingMessages;
@@ -256,7 +258,7 @@ public class Peer {
 		this.connectionTimestamp = NTP.getTime();
 		this.socketChannel.setOption(StandardSocketOptions.TCP_NODELAY, true);
 		this.socketChannel.configureBlocking(false);
-		this.byteBuffer = ByteBuffer.allocate(Network.getInstance().getMaxMessageSize());
+		this.byteBuffer = null; // Defer allocation to when we need it, to save memory. Sorry GC!
 		this.replyQueues = Collections.synchronizedMap(new HashMap<Integer, BlockingQueue<Message>>());
 		this.pendingMessages = new LinkedBlockingQueue<>();
 	}
@@ -292,11 +294,15 @@ public class Peer {
 	 * @throws IOException
 	 */
 	/* package */ void readChannel() throws IOException {
-		synchronized (this.byteBuffer) {
+		synchronized (this.byteBufferLock) {
 			while(true) {
 				if (!this.socketChannel.isOpen() || this.socketChannel.socket().isClosed())
 					return;
 
+				// Do we need to allocate byteBuffer?
+				if (this.byteBuffer == null)
+					this.byteBuffer = ByteBuffer.allocate(Network.getInstance().getMaxMessageSize());
+
 				final int bytesRead = this.socketChannel.read(this.byteBuffer);
 				if (bytesRead == -1) {
 					this.disconnect("EOF");
@@ -318,9 +324,15 @@ public class Peer {
 						return;
 					}
 
-					if (message == null && bytesRead == 0 && !wasByteBufferFull)
+					if (message == null && bytesRead == 0 && !wasByteBufferFull) {
 						// No complete message in buffer, no more bytes to read from socket even though there was room to read bytes
+
+						// If byteBuffer is empty then we can deallocate it, to save memory, albeit costing GC
+						if (this.byteBuffer.remaining() == this.byteBuffer.capacity())
+							this.byteBuffer = null;
+
 						return;
+					}
 
 					if (message == null)
 						// No complete message in buffer, but maybe more bytes to read from socket