聊聊SkyWalkingAgent

序

本文主要研究一下SkyWalkingAgent

SkyWalkingAgent

skywalking-6.6.0/apm-sniffer/apm-agent/src/main/java/org/apache/skywalking/apm/agent/SkyWalkingAgent.java

public class SkyWalkingAgent {
    private static final ILog logger = LogManager.getLogger(SkyWalkingAgent.class);

    /**
     * Main entrance. Use byte-buddy transform to enhance all classes, which define in plugins.
     *
     * @param agentArgs
     * @param instrumentation
     * @throws PluginException
     */
    public static void premain(String agentArgs, Instrumentation instrumentation) throws PluginException, IOException {
        final PluginFinder pluginFinder;
        try {
            SnifferConfigInitializer.initialize(agentArgs);

            pluginFinder = new PluginFinder(new PluginBootstrap().loadPlugins());

        } catch (ConfigNotFoundException ce) {
            logger.error(ce, "SkyWalking agent could not find config. Shutting down.");
            return;
        } catch (AgentPackageNotFoundException ape) {
            logger.error(ape, "Locate agent.jar failure. Shutting down.");
            return;
        } catch (Exception e) {
            logger.error(e, "SkyWalking agent initialized failure. Shutting down.");
            return;
        }

        final ByteBuddy byteBuddy = new ByteBuddy()
            .with(TypeValidation.of(Config.Agent.IS_OPEN_DEBUGGING_CLASS));

        AgentBuilder agentBuilder = new AgentBuilder.Default(byteBuddy)
            .ignore(
                nameStartsWith("net.bytebuddy.")
                    .or(nameStartsWith("org.slf4j."))
                    .or(nameStartsWith("org.groovy."))
                    .or(nameContains("javassist"))
                    .or(nameContains(".asm."))
                    .or(nameContains(".reflectasm."))
                    .or(nameStartsWith("sun.reflect"))
                    .or(allSkyWalkingAgentExcludeToolkit())
                    .or(ElementMatchers.<TypeDescription>isSynthetic()));

        JDK9ModuleExporter.EdgeClasses edgeClasses = new JDK9ModuleExporter.EdgeClasses();
        try {
            agentBuilder = BootstrapInstrumentBoost.inject(pluginFinder, instrumentation, agentBuilder, edgeClasses);
        } catch (Exception e) {
            logger.error(e, "SkyWalking agent inject bootstrap instrumentation failure. Shutting down.");
            return;
        }

        try {
            agentBuilder = JDK9ModuleExporter.openReadEdge(instrumentation, agentBuilder, edgeClasses);
        } catch (Exception e) {
            logger.error(e, "SkyWalking agent open read edge in JDK 9+ failure. Shutting down.");
            return;
        }

        agentBuilder
            .type(pluginFinder.buildMatch())
            .transform(new Transformer(pluginFinder))
            .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
            .with(new Listener())
            .installOn(instrumentation);

        try {
            ServiceManager.INSTANCE.boot();
        } catch (Exception e) {
            logger.error(e, "Skywalking agent boot failure.");
        }

        Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
            @Override public void run() {
                ServiceManager.INSTANCE.shutdown();
            }
        }, "skywalking service shutdown thread"));
    }

    //......
}

• SkyWalkingAgent的premain方法首先通过SnifferConfigInitializer.initialize(agentArgs)进行初始化，然后执行new PluginFinder(new PluginBootstrap().loadPlugins())，之后创建AgentBuilder，设置ignore、type、transform、listener然后install；最后执行ServiceManager.INSTANCE.boot()并注册shutdownHook执行ServiceManager.INSTANCE.shutdown()

SnifferConfigInitializer

skywalking-6.6.0/apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/conf/SnifferConfigInitializer.java

public class SnifferConfigInitializer {
    private static final ILog logger = LogManager.getLogger(SnifferConfigInitializer.class);
    private static String SPECIFIED_CONFIG_PATH = "skywalking_config";
    private static String DEFAULT_CONFIG_FILE_NAME = "/config/agent.config";
    private static String ENV_KEY_PREFIX = "skywalking.";
    private static boolean IS_INIT_COMPLETED = false;

    /**
     * If the specified agent config path is set, the agent will try to locate the specified agent config. If the
     * specified agent config path is not set , the agent will try to locate `agent.config`, which should be in the
     * /config directory of agent package.
     * <p>
     * Also try to override the config by system.properties. All the keys in this place should
     * start with {@link #ENV_KEY_PREFIX}. e.g. in env `skywalking.agent.service_name=yourAppName` to override
     * `agent.service_name` in config file.
     * <p>
     * At the end, `agent.service_name` and `collector.servers` must not be blank.
     */
    public static void initialize(String agentOptions) throws ConfigNotFoundException, AgentPackageNotFoundException {
        InputStreamReader configFileStream;

        try {
            configFileStream = loadConfig();
            Properties properties = new Properties();
            properties.load(configFileStream);
            for (String key : properties.stringPropertyNames()) {
                String value = (String)properties.get(key);
                //replace the key's value. properties.replace(key,value) in jdk8+
                properties.put(key, PropertyPlaceholderHelper.INSTANCE.replacePlaceholders(value, properties));
            }
            ConfigInitializer.initialize(properties, Config.class);
        } catch (Exception e) {
            logger.error(e, "Failed to read the config file, skywalking is going to run in default config.");
        }

        try {
            overrideConfigBySystemProp();
        } catch (Exception e) {
            logger.error(e, "Failed to read the system properties.");
        }

        if (!StringUtil.isEmpty(agentOptions)) {
            try {
                agentOptions = agentOptions.trim();
                logger.info("Agent options is {}.", agentOptions);

                overrideConfigByAgentOptions(agentOptions);
            } catch (Exception e) {
                logger.error(e, "Failed to parse the agent options, val is {}.", agentOptions);
            }
        }

        if (StringUtil.isEmpty(Config.Agent.SERVICE_NAME)) {
            throw new ExceptionInInitializerError("`agent.service_name` is missing.");
        }
        if (StringUtil.isEmpty(Config.Collector.BACKEND_SERVICE)) {
            throw new ExceptionInInitializerError("`collector.backend_service` is missing.");
        }
        if (Config.Plugin.PEER_MAX_LENGTH <= 3) {
            logger.warn("PEER_MAX_LENGTH configuration:{} error, the default value of 200 will be used.", Config.Plugin.PEER_MAX_LENGTH);
            Config.Plugin.PEER_MAX_LENGTH = 200;
        }

        IS_INIT_COMPLETED = true;
    }

    //......
}

• SnifferConfigInitializer主要用于加载skywalking的配置文件，默认是读取/config/agent.config文件

PluginBootstrap

skywalking-6.6.0/apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/plugin/PluginBootstrap.java

public class PluginBootstrap {
    private static final ILog logger = LogManager.getLogger(PluginBootstrap.class);

    /**
     * load all plugins.
     *
     * @return plugin definition list.
     */
    public List<AbstractClassEnhancePluginDefine> loadPlugins() throws AgentPackageNotFoundException {
        AgentClassLoader.initDefaultLoader();

        PluginResourcesResolver resolver = new PluginResourcesResolver();
        List<URL> resources = resolver.getResources();

        if (resources == null || resources.size() == 0) {
            logger.info("no plugin files (skywalking-plugin.def) found, continue to start application.");
            return new ArrayList<AbstractClassEnhancePluginDefine>();
        }

        for (URL pluginUrl : resources) {
            try {
                PluginCfg.INSTANCE.load(pluginUrl.openStream());
            } catch (Throwable t) {
                logger.error(t, "plugin file [{}] init failure.", pluginUrl);
            }
        }

        List<PluginDefine> pluginClassList = PluginCfg.INSTANCE.getPluginClassList();

        List<AbstractClassEnhancePluginDefine> plugins = new ArrayList<AbstractClassEnhancePluginDefine>();
        for (PluginDefine pluginDefine : pluginClassList) {
            try {
                logger.debug("loading plugin class {}.", pluginDefine.getDefineClass());
                AbstractClassEnhancePluginDefine plugin =
                    (AbstractClassEnhancePluginDefine)Class.forName(pluginDefine.getDefineClass(),
                        true,
                        AgentClassLoader.getDefault())
                        .newInstance();
                plugins.add(plugin);
            } catch (Throwable t) {
                logger.error(t, "load plugin [{}] failure.", pluginDefine.getDefineClass());
            }
        }

        plugins.addAll(DynamicPluginLoader.INSTANCE.load(AgentClassLoader.getDefault()));

        return plugins;

    }

}

• PluginBootstrap提供了loadPlugins方法，它通过PluginResourcesResolver来加载skywalking-plugin.def定义的plugin

PluginFinder

skywalking-6.6.0/apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/plugin/PluginFinder.java

public class PluginFinder {
    private final Map<String, LinkedList<AbstractClassEnhancePluginDefine>> nameMatchDefine = new HashMap<String, LinkedList<AbstractClassEnhancePluginDefine>>();
    private final List<AbstractClassEnhancePluginDefine> signatureMatchDefine = new ArrayList<AbstractClassEnhancePluginDefine>();
    private final List<AbstractClassEnhancePluginDefine> bootstrapClassMatchDefine = new ArrayList<AbstractClassEnhancePluginDefine>();

    public PluginFinder(List<AbstractClassEnhancePluginDefine> plugins) {
        for (AbstractClassEnhancePluginDefine plugin : plugins) {
            ClassMatch match = plugin.enhanceClass();

            if (match == null) {
                continue;
            }

            if (match instanceof NameMatch) {
                NameMatch nameMatch = (NameMatch)match;
                LinkedList<AbstractClassEnhancePluginDefine> pluginDefines = nameMatchDefine.get(nameMatch.getClassName());
                if (pluginDefines == null) {
                    pluginDefines = new LinkedList<AbstractClassEnhancePluginDefine>();
                    nameMatchDefine.put(nameMatch.getClassName(), pluginDefines);
                }
                pluginDefines.add(plugin);
            } else {
                signatureMatchDefine.add(plugin);
            }

            if (plugin.isBootstrapInstrumentation()) {
                bootstrapClassMatchDefine.add(plugin);
            }
        }
    }

    public List<AbstractClassEnhancePluginDefine> find(TypeDescription typeDescription) {
        List<AbstractClassEnhancePluginDefine> matchedPlugins = new LinkedList<AbstractClassEnhancePluginDefine>();
        String typeName = typeDescription.getTypeName();
        if (nameMatchDefine.containsKey(typeName)) {
            matchedPlugins.addAll(nameMatchDefine.get(typeName));
        }

        for (AbstractClassEnhancePluginDefine pluginDefine : signatureMatchDefine) {
            IndirectMatch match = (IndirectMatch)pluginDefine.enhanceClass();
            if (match.isMatch(typeDescription)) {
                matchedPlugins.add(pluginDefine);
            }
        }

        return matchedPlugins;
    }

    public ElementMatcher<? super TypeDescription> buildMatch() {
        ElementMatcher.Junction judge = new AbstractJunction<NamedElement>() {
            @Override
            public boolean matches(NamedElement target) {
                return nameMatchDefine.containsKey(target.getActualName());
            }
        };
        judge = judge.and(not(isInterface()));
        for (AbstractClassEnhancePluginDefine define : signatureMatchDefine) {
            ClassMatch match = define.enhanceClass();
            if (match instanceof IndirectMatch) {
                judge = judge.or(((IndirectMatch)match).buildJunction());
            }
        }
        return new ProtectiveShieldMatcher(judge);
    }

    public List<AbstractClassEnhancePluginDefine> getBootstrapClassMatchDefine() {
        return bootstrapClassMatchDefine;
    }
}

• PluginFinder的构造器接收AbstractClassEnhancePluginDefine列表，并提供了find方法用于根据typeDescription查找匹配的AbstractClassEnhancePluginDefine，以及buildMatch方法用于构造ProtectiveShieldMatcher

Transformer

skywalking-6.6.0/apm-sniffer/apm-agent/src/main/java/org/apache/skywalking/apm/agent/SkyWalkingAgent.java

    private static class Transformer implements AgentBuilder.Transformer {
        private PluginFinder pluginFinder;

        Transformer(PluginFinder pluginFinder) {
            this.pluginFinder = pluginFinder;
        }

        @Override
        public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDescription typeDescription,
            ClassLoader classLoader, JavaModule module) {
            List<AbstractClassEnhancePluginDefine> pluginDefines = pluginFinder.find(typeDescription);
            if (pluginDefines.size() > 0) {
                DynamicType.Builder<?> newBuilder = builder;
                EnhanceContext context = new EnhanceContext();
                for (AbstractClassEnhancePluginDefine define : pluginDefines) {
                    DynamicType.Builder<?> possibleNewBuilder = define.define(typeDescription, newBuilder, classLoader, context);
                    if (possibleNewBuilder != null) {
                        newBuilder = possibleNewBuilder;
                    }
                }
                if (context.isEnhanced()) {
                    logger.debug("Finish the prepare stage for {}.", typeDescription.getName());
                }

                return newBuilder;
            }

            logger.debug("Matched class {}, but ignore by finding mechanism.", typeDescription.getTypeName());
            return builder;
        }
    }

• Transformer实现了AgentBuilder.Transformer接口，其构造器要求输入pluginFinder；其transform方法通过pluginFinder.find(typeDescription)获取指定的pluginDefines，若不为空则遍历pluginDefines进行define返回possibleNewBuilder

Listener

skywalking-6.6.0/apm-sniffer/apm-agent/src/main/java/org/apache/skywalking/apm/agent/SkyWalkingAgent.java

    private static class Listener implements AgentBuilder.Listener {
        @Override
        public void onDiscovery(String typeName, ClassLoader classLoader, JavaModule module, boolean loaded) {

        }

        @Override
        public void onTransformation(TypeDescription typeDescription, ClassLoader classLoader, JavaModule module,
            boolean loaded, DynamicType dynamicType) {
            if (logger.isDebugEnable()) {
                logger.debug("On Transformation class {}.", typeDescription.getName());
            }

            InstrumentDebuggingClass.INSTANCE.log(dynamicType);
        }

        @Override
        public void onIgnored(TypeDescription typeDescription, ClassLoader classLoader, JavaModule module,
            boolean loaded) {

        }

        @Override
        public void onError(String typeName, ClassLoader classLoader, JavaModule module, boolean loaded,
            Throwable throwable) {
            logger.error("Enhance class " + typeName + " error.", throwable);
        }

        @Override
        public void onComplete(String typeName, ClassLoader classLoader, JavaModule module, boolean loaded) {
        }
    }

• Listener实现了AgentBuilder.Listener接口，其onTransformation方法会进行打印debug日志，以及执行InstrumentDebuggingClass.INSTANCE.log(dynamicType)；其onError方法则会打印error日志

ServiceManager

skywalking-6.6.0/apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/boot/ServiceManager.java

public enum ServiceManager {
    INSTANCE;

    private static final ILog logger = LogManager.getLogger(ServiceManager.class);
    private Map<Class, BootService> bootedServices = Collections.emptyMap();

    public void boot() {
        bootedServices = loadAllServices();

        prepare();
        startup();
        onComplete();
    }

    public void shutdown() {
        for (BootService service : bootedServices.values()) {
            try {
                service.shutdown();
            } catch (Throwable e) {
                logger.error(e, "ServiceManager try to shutdown [{}] fail.", service.getClass().getName());
            }
        }
    }

    private Map<Class, BootService> loadAllServices() {
        Map<Class, BootService> bootedServices = new LinkedHashMap<Class, BootService>();
        List<BootService> allServices = new LinkedList<BootService>();
        load(allServices);
        Iterator<BootService> serviceIterator = allServices.iterator();
        while (serviceIterator.hasNext()) {
            BootService bootService = serviceIterator.next();

            Class<? extends BootService> bootServiceClass = bootService.getClass();
            boolean isDefaultImplementor = bootServiceClass.isAnnotationPresent(DefaultImplementor.class);
            if (isDefaultImplementor) {
                if (!bootedServices.containsKey(bootServiceClass)) {
                    bootedServices.put(bootServiceClass, bootService);
                } else {
                    //ignore the default service
                }
            } else {
                OverrideImplementor overrideImplementor = bootServiceClass.getAnnotation(OverrideImplementor.class);
                if (overrideImplementor == null) {
                    if (!bootedServices.containsKey(bootServiceClass)) {
                        bootedServices.put(bootServiceClass, bootService);
                    } else {
                        throw new ServiceConflictException("Duplicate service define for :" + bootServiceClass);
                    }
                } else {
                    Class<? extends BootService> targetService = overrideImplementor.value();
                    if (bootedServices.containsKey(targetService)) {
                        boolean presentDefault = bootedServices.get(targetService).getClass().isAnnotationPresent(DefaultImplementor.class);
                        if (presentDefault) {
                            bootedServices.put(targetService, bootService);
                        } else {
                            throw new ServiceConflictException("Service " + bootServiceClass + " overrides conflict, " +
                                "exist more than one service want to override :" + targetService);
                        }
                    } else {
                        bootedServices.put(targetService, bootService);
                    }
                }
            }

        }
        return bootedServices;
    }

    private void prepare() {
        for (BootService service : bootedServices.values()) {
            try {
                service.prepare();
            } catch (Throwable e) {
                logger.error(e, "ServiceManager try to pre-start [{}] fail.", service.getClass().getName());
            }
        }
    }

    private void startup() {
        for (BootService service : bootedServices.values()) {
            try {
                service.boot();
            } catch (Throwable e) {
                logger.error(e, "ServiceManager try to start [{}] fail.", service.getClass().getName());
            }
        }
    }

    private void onComplete() {
        for (BootService service : bootedServices.values()) {
            try {
                service.onComplete();
            } catch (Throwable e) {
                logger.error(e, "Service [{}] AfterBoot process fails.", service.getClass().getName());
            }
        }
    }

    /**
     * Find a {@link BootService} implementation, which is already started.
     *
     * @param serviceClass class name.
     * @param <T> {@link BootService} implementation class.
     * @return {@link BootService} instance
     */
    public <T extends BootService> T findService(Class<T> serviceClass) {
        return (T)bootedServices.get(serviceClass);
    }

    void load(List<BootService> allServices) {
        Iterator<BootService> iterator = ServiceLoader.load(BootService.class, AgentClassLoader.getDefault()).iterator();
        while (iterator.hasNext()) {
            allServices.add(iterator.next());
        }
    }
}

• ServiceManager是个枚举，它有个INSTANCE单例，其boot方法主要执行loadAllServices、prepare、startup、onComplete；其shutdown方法则遍历bootedServices挨个执行service.shutdown()；loadAllServices方法通过ServiceLoader.load(BootService.class, AgentClassLoader.getDefault()).iterator()加载BootService；prepare、startup、onComplete都是遍历bootedServices分别执行service.prepare()、service.boot()、service.onComplete()

小结

SkyWalkingAgent的premain方法首先通过SnifferConfigInitializer.initialize(agentArgs)进行初始化，然后执行new PluginFinder(new PluginBootstrap().loadPlugins())，之后创建AgentBuilder，设置ignore、type、transform、listener然后install；最后执行ServiceManager.INSTANCE.boot()并注册shutdownHook执行ServiceManager.INSTANCE.shutdown()

doc

• SkyWalkingAgent