[Core] Use meaningful thread names (#1623)

Before it was using the standard threadfactory, which
was naming threads like `pool-x-thread-y`. Now it is
`cucumber-runner-y-thread-x`. This better for logging to
 see which threads belong to cucumber and which are
unrelated background

Author: kutzi

core/src/main/java/cucumber/runtime/Runtime.java

@@ -26,7 +26,9 @@
 import java.util.concurrent.AbstractExecutorService;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
 
 /**
  * This is the main entry point for running Cucumber features from the CLI.
@@ -195,7 +197,7 @@ public Runtime build() {
                 : new SingletonRunnerSupplier(this.runtimeOptions, eventBus, backendSupplier);
 
             final ExecutorService executor = runtimeOptions.isMultiThreaded()
-                ? Executors.newFixedThreadPool(runtimeOptions.getThreads())
+                ? Executors.newFixedThreadPool(runtimeOptions.getThreads(), new CucumberThreadFactory())
                 : new SameThreadExecutorService();
 
 
@@ -210,6 +212,22 @@ public Runtime build() {
         }
     }
 
+    private static final class CucumberThreadFactory implements ThreadFactory {
+
+        private static final AtomicInteger poolNumber = new AtomicInteger(1);
+        private final AtomicInteger threadNumber = new AtomicInteger(1);
+        private final String namePrefix;
+
+        CucumberThreadFactory() {
+            this.namePrefix = "cucumber-runner-" + poolNumber.getAndIncrement() + "-thread-";
+        }
+        
+        @Override
+        public Thread newThread(Runnable r) {
+            return new Thread(r, namePrefix + this.threadNumber.getAndIncrement());
+        }
+    }
+
     private static final class SameThreadExecutorService extends AbstractExecutorService {
 
         @Override