Set Emitter's threads name for easier debugging (close #280)

src/main/java/com/snowplowanalytics/snowplow/tracker/emitter/AbstractEmitter.java

@@ -15,6 +15,8 @@
 import java.util.List;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import com.google.common.base.Preconditions;
 
@@ -131,10 +133,11 @@ protected AbstractEmitter(final Builder<?> builder) {
         }
 
         this.requestCallback = builder.requestCallback;
+
         if (builder.requestExecutorService != null) {
             this.executor = builder.requestExecutorService;
         } else {
-            this.executor = Executors.newScheduledThreadPool(builder.threadCount);
+            this.executor = Executors.newScheduledThreadPool(builder.threadCount, new EmitterThreadFactory());
         }
     }
 
@@ -195,4 +198,34 @@ protected void execute(final Runnable runnable) {
     protected boolean isSuccessfulSend(final int code) {
         return code >= 200 && code < 300;
     }
+
+    /**
+     * Copied from `Executors.defaultThreadFactory()`.
+     * The only change is the generated name prefix.
+     */
+    static class EmitterThreadFactory implements ThreadFactory {
+        private static final AtomicInteger poolNumber = new AtomicInteger(1);
+        private final ThreadGroup group;
+        private final AtomicInteger threadNumber = new AtomicInteger(1);
+        private final String namePrefix;
+
+        EmitterThreadFactory() {
+            SecurityManager securityManager = System.getSecurityManager();
+            this.group = securityManager != null ? securityManager.getThreadGroup() : Thread.currentThread().getThreadGroup();
+            this.namePrefix = "snowplow-emitter-pool-" + poolNumber.getAndIncrement() + "-request-thread-";
+        }
+
+        public Thread newThread(Runnable runnable) {
+            Thread thread = new Thread(this.group, runnable, this.namePrefix + this.threadNumber.getAndIncrement(), 0L);
+            if (thread.isDaemon()) {
+                thread.setDaemon(false);
+            }
+
+            if (thread.getPriority() != 5) {
+                thread.setPriority(5);
+            }
+
+            return thread;
+        }
+    }
 }

src/main/java/com/snowplowanalytics/snowplow/tracker/emitter/BatchEmitter.java

@@ -20,6 +20,7 @@
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import com.google.common.base.Preconditions;
 import com.snowplowanalytics.snowplow.tracker.constants.Constants;
@@ -38,6 +39,8 @@
 public class BatchEmitter extends AbstractEmitter implements Closeable {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(BatchEmitter.class);
+    private static final AtomicInteger BUFFER_CONSUMER_THREAD_NUMBER = new AtomicInteger(1);
+    private static final String BUFFER_CONSUMER_THREAD_NAME_PREFIX = "snowplow-emitter-BufferConsumer-thread-";
 
     private final Thread bufferConsumer;
     private boolean isClosing = false;
@@ -89,7 +92,10 @@ protected BatchEmitter(final Builder<?> builder) {
 
         this.bufferSize = builder.bufferSize;
 
-        bufferConsumer = new Thread(getBufferConsumerRunnable());
+        bufferConsumer = new Thread(
+                getBufferConsumerRunnable(),
+                BUFFER_CONSUMER_THREAD_NAME_PREFIX + BUFFER_CONSUMER_THREAD_NUMBER.getAndIncrement()
+        );
         bufferConsumer.start();
     }