make tests more robust

1. we are now using a random port for listening
2. TcpIngestor.start() waits until the socket is established.

pdb-ui/src/main/java/org/lucares/pdbui/TcpIngestor.java

@@ -6,9 +6,11 @@ import java.net.Socket;
 import java.net.SocketTimeoutException;
 import java.nio.file.Path;
 import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import javax.annotation.PreDestroy;
@@ -20,7 +22,6 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Component;
 
 @Component
@@ -37,6 +38,8 @@ public class TcpIngestor implements Ingestor, AutoCloseable, DisposableBean {
 
     private final PerformanceDb db;
 
+    private volatile int port = PORT;
+
     public TcpIngestor(final Path dataDirectory) throws IOException {
         LOGGER.info("opening performance db: " + dataDirectory);
         db = new PerformanceDb(dataDirectory);
@@ -48,23 +51,42 @@ public class TcpIngestor implements Ingestor, AutoCloseable, DisposableBean {
         this.db = db;
     }
 
+    public void useRandomPort() {
+        port = 0;
+    }
+
+    /**
+     * Returns the port used. If {@link #useRandomPort()} is used then the port may
+     * be null until the socket is open.
+     * 
+     * @return the port used
+     */
+    public int getPort() {
+        return port;
+    }
+
     public PerformanceDb getDb() {
         return db;
     }
 
-    @Async
     @Override
     public void start() throws Exception {
-
-        serverThreadPool.submit(() -> listen());
+        final CountDownLatch started = new CountDownLatch(1);
+        serverThreadPool.submit(() -> listen(started));
+        final boolean startedSuccessfully = started.await(5, TimeUnit.SECONDS);
+        if (!startedSuccessfully) {
+            throw new TimeoutException("failed to start listener");
+        }
     }
 
-    private Void listen() throws IOException {
+    private Void listen(final CountDownLatch started) throws IOException {
         Thread.currentThread().setName("socket-listener");
-        try (ServerSocket serverSocket = new ServerSocket(PORT);) {
-            LOGGER.info("listening on port " + PORT);
+        try (ServerSocket serverSocket = new ServerSocket(port);) {
+            port = serverSocket.getLocalPort();
+            LOGGER.info("listening on port " + serverSocket.getLocalPort());
 
             serverSocket.setSoTimeout((int) TimeUnit.MILLISECONDS.toMillis(2));
+            started.countDown(); // notify caller that the socket is now listening
 
             while (acceptNewConnections.get()) {
                 try {