Add BlockHound integration that detects blocking calls in event loops (#9687)

Motivation:

Netty is an asynchronous framework.
If somebody uses a blocking call inside Netty's event loops,
it may lead to a severe performance degradation.
BlockHound is a tool that helps detecting such calls.

Modifications:

This change adds a BlockHound's SPI integration that marks
threads created by Netty (`FastThreadLocalThread`s) as non-blocking.
It also marks some of Netty's internal methods as whitelisted
as they are required to run the event loops.

Result:

When BlockHound is installed, any blocking call inside event loops
is intercepted and reported (by default an error will be thrown).

common/pom.xml

@@ -78,6 +78,11 @@
       <artifactId>log4j-core</artifactId>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>io.projectreactor.tools</groupId>
+      <artifactId>blockhound</artifactId>
+      <optional>true</optional>
+    </dependency>
     <dependency>
       <groupId>org.mockito</groupId>
       <artifactId>mockito-core</artifactId>

common/src/main/java/io/netty/util/internal/Hidden.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2019 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+package io.netty.util.internal;
+
+import io.netty.util.concurrent.FastThreadLocalThread;
+import reactor.blockhound.BlockHound;
+import reactor.blockhound.integration.BlockHoundIntegration;
+
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+/**
+ * Contains classes that must be have public visibility but are not public API.
+ */
+class Hidden {
+
+    /**
+     * This class integrates Netty with BlockHound.
+     * <p>
+     * It is public but only because of the ServiceLoader's limitations
+     * and SHOULD NOT be considered a public API.
+     */
+    @UnstableApi
+    @SuppressJava6Requirement(reason = "BlockHound is Java 8+, but this class is only loaded by it's SPI")
+    public static final class NettyBlockHoundIntegration implements BlockHoundIntegration {
+
+        @Override
+        public void applyTo(BlockHound.Builder builder) {
+            builder.allowBlockingCallsInside(
+                    "io.netty.channel.nio.NioEventLoop",
+                    "handleLoopException"
+            );
+
+            builder.allowBlockingCallsInside(
+                    "io.netty.channel.kqueue.KQueueEventLoop",
+                    "handleLoopException"
+            );
+
+            builder.allowBlockingCallsInside(
+                    "io.netty.channel.epoll.EpollEventLoop",
+                    "handleLoopException"
+            );
+
+            builder.allowBlockingCallsInside(
+                    "io.netty.util.HashedWheelTimer$Worker",
+                    "waitForNextTick"
+            );
+
+            builder.allowBlockingCallsInside(
+                    "io.netty.util.concurrent.SingleThreadEventExecutor",
+                    "confirmShutdown"
+            );
+
+            builder.nonBlockingThreadPredicate(new Function<Predicate<Thread>, Predicate<Thread>>() {
+                @Override
+                public Predicate<Thread> apply(final Predicate<Thread> p) {
+                    return new Predicate<Thread>() {
+                        @Override
+                        @SuppressJava6Requirement(reason = "Predicate#test")
+                        public boolean test(Thread thread) {
+                            return p.test(thread) || thread instanceof FastThreadLocalThread;
+                        }
+                    };
+                }
+            });
+        }
+
+        @Override
+        public int compareTo(BlockHoundIntegration o) {
+            return 0;
+        }
+    }
+}

common/src/main/resources/META-INF/services/reactor.blockhound.integration.BlockHoundIntegration

@@ -0,0 +1,14 @@
+# Copyright 2019 The Netty Project
+#
+# The Netty Project licenses this file to you under the Apache License,
+# version 2.0 (the "License"); you may not use this file except in compliance
+# with the License. You may obtain a copy of the License at:
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+io.netty.util.internal.Hidden$NettyBlockHoundIntegration

pom.xml

@@ -375,6 +375,7 @@
     <module>testsuite-osgi</module>
     <module>testsuite-shading</module>
     <module>testsuite-native-image</module>
+    <module>transport-blockhound-tests</module>
     <module>microbench</module>
     <module>bom</module>
   </modules>
@@ -674,6 +675,13 @@
         <version>${log4j2.version}</version>
         <scope>test</scope>
       </dependency>
+
+      <!-- BlockHound integration -->
+      <dependency>
+        <groupId>io.projectreactor.tools</groupId>
+        <artifactId>blockhound</artifactId>
+        <version>1.0.1.RELEASE</version>
+      </dependency>
     </dependencies>
   </dependencyManagement>
 

transport-blockhound-tests/pom.xml

@@ -0,0 +1,53 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ Copyright 2019 The Netty Project
+  ~
+  ~ The Netty Project licenses this file to you under the Apache License,
+  ~ version 2.0 (the "License"); you may not use this file except in compliance
+  ~ with the License. You may obtain a copy of the License at:
+  ~
+  ~   http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+  ~ WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+  ~ License for the specific language governing permissions and limitations
+  ~ under the License.
+  -->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>io.netty</groupId>
+    <artifactId>netty-parent</artifactId>
+    <version>4.1.43.Final-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>netty-transport-blockhound-tests</artifactId>
+  <packaging>jar</packaging>
+  <description>
+    Tests for the BlockHound integration.
+  </description>
+
+  <name>Netty/Transport/BlockHound/Tests</name>
+
+  <properties>
+    <maven.compiler.source>1.8</maven.compiler.source>
+    <maven.compiler.target>1.8</maven.compiler.target>
+    <skipJapicmp>true</skipJapicmp>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>${project.groupId}</groupId>
+      <artifactId>netty-transport</artifactId>
+      <version>${project.version}</version>
+    </dependency>
+
+    <dependency>
+      <groupId>io.projectreactor.tools</groupId>
+      <artifactId>blockhound</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

transport-blockhound-tests/src/test/java/io/netty/util/internal/NettyBlockHoundIntegrationTest.java

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2019 The Netty Project
+
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+
+ * http://www.apache.org/licenses/LICENSE-2.0
+
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.util.internal;
+
+import io.netty.util.concurrent.GlobalEventExecutor;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import reactor.blockhound.BlockHound;
+
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.FutureTask;
+import java.util.concurrent.TimeUnit;
+
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+public class NettyBlockHoundIntegrationTest {
+
+    @BeforeClass
+    public static void setUpClass() {
+        BlockHound.install();
+    }
+
+    @Test
+    public void testBlockingCallsInNettyThreads() throws Exception {
+        final FutureTask<Void> future = new FutureTask<>(() -> {
+            Thread.sleep(0);
+            return null;
+        });
+        GlobalEventExecutor.INSTANCE.execute(future);
+
+        try {
+            future.get(5, TimeUnit.SECONDS);
+            fail("Expected an exception due to a blocking call but none was thrown");
+        } catch (ExecutionException e) {
+            Throwable throwable = e.getCause();
+            assertNotNull("An exception was thrown", throwable);
+            assertTrue("Blocking call was reported", throwable.getMessage().contains("Blocking call"));
+        }
+    }
+}