HSEARCH-3739 Add ThreadSpy to execute assertions on threads created by Hibernate Search

Author: yrodiere

util/internal/integrationtest/common/src/main/java/org/hibernate/search/util/impl/integrationtest/common/rule/ThreadSpy.java

@@ -0,0 +1,106 @@
+/*
+ * Hibernate Search, full-text search for your domain model
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.search.util.impl.integrationtest.common.rule;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Locale;
+import java.util.concurrent.ThreadFactory;
+import java.util.stream.Collectors;
+
+import org.hibernate.search.engine.cfg.spi.EngineSpiSettings;
+import org.hibernate.search.engine.environment.bean.BeanHolder;
+import org.hibernate.search.engine.environment.bean.BeanReference;
+import org.hibernate.search.engine.environment.thread.spi.ThreadProvider;
+
+import org.junit.rules.TestRule;
+import org.junit.runner.Description;
+import org.junit.runners.model.Statement;
+
+/**
+ * Spy on the threads created by Hibernate Search.
+ * <p>
+ * To use this, configure a ThreadSpy instance as a {@code @Rule} in your test,
+ * then set {@link EngineSpiSettings#THREAD_PROVIDER} to the result of {@link ThreadSpy#getThreadProvider()}
+ * when starting Hibernate Search.
+ */
+public class ThreadSpy implements TestRule {
+	private List<Thread> createdThreads = Collections.synchronizedList( new ArrayList<>() );
+
+	@Override
+	public Statement apply(Statement base, Description description) {
+		return new Statement() {
+			@Override
+			public void evaluate() throws Throwable {
+				setup();
+				try {
+					base.evaluate();
+				}
+				finally {
+					tearDown();
+				}
+			}
+		};
+	}
+
+	public BeanReference<ThreadProvider> getThreadProvider() {
+		return beanResolver -> {
+			BeanHolder<? extends ThreadProvider> delegateHolder =
+					beanResolver.resolve( EngineSpiSettings.Defaults.THREAD_PROVIDER );
+			SpyingThreadProvider spyingFactory = new SpyingThreadProvider( delegateHolder.get() );
+			return BeanHolder.<ThreadProvider>of( spyingFactory )
+					.withDependencyAutoClosing( delegateHolder );
+		};
+	}
+
+	public List<Thread> getCreatedThreads(String stringInName) {
+		return createdThreads.stream()
+				.filter( t -> t.getName().toLowerCase( Locale.ROOT ).contains( stringInName.toLowerCase( Locale.ROOT ) ) )
+				.collect( Collectors.toList() );
+	}
+
+	private void setup() {
+	}
+
+	private void tearDown() {
+		createdThreads.clear();
+	}
+
+	private class SpyingThreadProvider implements ThreadProvider {
+		private final ThreadProvider delegate;
+
+		private SpyingThreadProvider(ThreadProvider delegate) {
+			this.delegate = delegate;
+		}
+
+		@Override
+		public String createThreadName(String prefix, int threadNumber) {
+			return delegate.createThreadName( prefix, threadNumber );
+		}
+
+		@Override
+		public ThreadFactory createThreadFactory(String prefix) {
+			return new SpyingThreadFactory( delegate.createThreadFactory( prefix ) );
+		}
+	}
+
+	private class SpyingThreadFactory implements ThreadFactory {
+		private final ThreadFactory delegate;
+
+		SpyingThreadFactory(ThreadFactory delegate) {
+			this.delegate = delegate;
+		}
+
+		@Override
+		public Thread newThread(Runnable r) {
+			Thread thread = delegate.newThread( r );
+			createdThreads.add( thread );
+			return thread;
+		}
+	}
+}