/**
* Copyright 2012 Netflix, Inc.
*
* Licensed 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 com.netflix.hystrix.strategy;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
import java.util.concurrent.atomic.AtomicReference;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import com.netflix.hystrix.strategy.concurrency.HystrixConcurrencyStrategy;
import com.netflix.hystrix.strategy.concurrency.HystrixConcurrencyStrategyDefault;
import com.netflix.hystrix.strategy.eventnotifier.HystrixEventNotifier;
import com.netflix.hystrix.strategy.eventnotifier.HystrixEventNotifierDefault;
import com.netflix.hystrix.strategy.executionhook.HystrixCommandExecutionHook;
import com.netflix.hystrix.strategy.executionhook.HystrixCommandExecutionHookDefault;
import com.netflix.hystrix.strategy.metrics.HystrixMetricsPublisher;
import com.netflix.hystrix.strategy.metrics.HystrixMetricsPublisherDefault;
import com.netflix.hystrix.strategy.metrics.HystrixMetricsPublisherFactory;
import com.netflix.hystrix.strategy.properties.HystrixDynamicProperties;
import com.netflix.hystrix.strategy.properties.HystrixDynamicPropertiesSystemProperties;
import com.netflix.hystrix.strategy.properties.HystrixPropertiesStrategy;
import com.netflix.hystrix.strategy.properties.HystrixPropertiesStrategyDefault;
/**
* Registry for plugin implementations that allows global override and handles the retrieval of correct implementation based on order of precedence:
* <ol>
* <li>plugin registered globally via <code>register</code> methods in this class</li>
* <li>plugin registered and retrieved using the resolved {@link HystrixDynamicProperties} (usually Archaius, see get methods for property names)</li>
* <li>plugin registered and retrieved using the JDK {@link ServiceLoader}</li>
* <li>default implementation</li>
* </ol>
*
* The exception to the above order is the {@link HystrixDynamicProperties} implementation
* which is only loaded through <code>System.properties</code> or the ServiceLoader (see the {@link HystrixPlugins#getDynamicProperties() getter} for more details).
* <p>
* See the Hystrix GitHub Wiki for more information: <a href="https://github.com/Netflix/Hystrix/wiki/Plugins">https://github.com/Netflix/Hystrix/wiki/Plugins</a>.
*/
public class HystrixPlugins {
//We should not load unless we are requested to. This avoids accidental initialization. @agentgt
//See https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
private static class LazyHolder { private static final HystrixPlugins INSTANCE = HystrixPlugins.create(); }
private final ClassLoader classLoader;
/* package */ final AtomicReference<HystrixEventNotifier> notifier = new AtomicReference<HystrixEventNotifier>();
/* package */ final AtomicReference<HystrixConcurrencyStrategy> concurrencyStrategy = new AtomicReference<HystrixConcurrencyStrategy>();
/* package */ final AtomicReference<HystrixMetricsPublisher> metricsPublisher = new AtomicReference<HystrixMetricsPublisher>();
/* package */ final AtomicReference<HystrixPropertiesStrategy> propertiesFactory = new AtomicReference<HystrixPropertiesStrategy>();
/* package */ final AtomicReference<HystrixCommandExecutionHook> commandExecutionHook = new AtomicReference<HystrixCommandExecutionHook>();
private final HystrixDynamicProperties dynamicProperties;
private HystrixPlugins(ClassLoader classLoader, LoggerSupplier logSupplier) {
//This will load Archaius if its in the classpath.
this.classLoader = classLoader;
//N.B. Do not use a logger before this is loaded as it will most likely load the configuration system.
//The configuration system may need to do something prior to loading logging. @agentgt
dynamicProperties = resolveDynamicProperties(classLoader, logSupplier);
}
/**
* For unit test purposes.
* @ExcludeFromJavadoc
*/
/* private */ static HystrixPlugins create(ClassLoader classLoader, LoggerSupplier logSupplier) {
return new HystrixPlugins(classLoader, logSupplier);
}
/**
* For unit test purposes.
* @ExcludeFromJavadoc
*/
/* private */ static HystrixPlugins create(ClassLoader classLoader) {
return new HystrixPlugins(classLoader, new LoggerSupplier() {
@Override
public Logger getLogger() {
return LoggerFactory.getLogger(HystrixPlugins.class);
}
});
}
/**
* @ExcludeFromJavadoc
*/
/* private */ static HystrixPlugins create() {
return create(HystrixPlugins.class.getClassLoader());
}
public static HystrixPlugins getInstance() {
return LazyHolder.INSTANCE;
}
/**
* Reset all of the HystrixPlugins to null. You may invoke this directly, or it also gets invoked via <code>Hystrix.reset()</code>
*/
public static void reset() {
getInstance().notifier.set(null);
getInstance().concurrencyStrategy.set(null);
getInstance().metricsPublisher.set(null);
getInstance().propertiesFactory.set(null);
getInstance().commandExecutionHook.set(null);
HystrixMetricsPublisherFactory.reset();
}
/**
* Retrieve instance of {@link HystrixEventNotifier} to use based on order of precedence as defined in {@link HystrixPlugins} class header.
* <p>
* Override default by using {@link #registerEventNotifier(HystrixEventNotifier)} or setting property (via Archaius): <code>hystrix.plugin.HystrixEventNotifier.implementation</code> with the full classname to
* load.
*
* @return {@link HystrixEventNotifier} implementation to use
*/
public HystrixEventNotifier getEventNotifier() {
if (notifier.get() == null) {
// check for an implementation from Archaius first
Object impl = getPluginImplementation(HystrixEventNotifier.class);
if (impl == null) {
// nothing set via Archaius so initialize with default
notifier.compareAndSet(null, HystrixEventNotifierDefault.getInstance());
// we don't return from here but call get() again in case of thread-race so the winner will always get returned
} else {
// we received an implementation from Archaius so use it
notifier.compareAndSet(null, (HystrixEventNotifier) impl);
}
}
return notifier.get();
}
/**
* Register a {@link HystrixEventNotifier} implementation as a global override of any injected or default implementations.
*
* @param impl
* {@link HystrixEventNotifier} implementation
* @throws IllegalStateException
* if called more than once or after the default was initialized (if usage occurs before trying to register)
*/
public void registerEventNotifier(HystrixEventNotifier impl) {
if (!notifier.compareAndSet(null, impl)) {
throw new IllegalStateException("Another strategy was already registered.");
}
}
/**
* Retrieve instance of {@link HystrixConcurrencyStrategy} to use based on order of precedence as defined in {@link HystrixPlugins} class header.
* <p>
* Override default by using {@link #registerConcurrencyStrategy(HystrixConcurrencyStrategy)} or setting property (via Archaius): <code>hystrix.plugin.HystrixConcurrencyStrategy.implementation</code> with the
* full classname to load.
*
* @return {@link HystrixConcurrencyStrategy} implementation to use
*/
public HystrixConcurrencyStrategy getConcurrencyStrategy() {
if (concurrencyStrategy.get() == null) {
// check for an implementation from Archaius first
Object impl = getPluginImplementation(HystrixConcurrencyStrategy.class);
if (impl == null) {
// nothing set via Archaius so initialize with default
concurrencyStrategy.compareAndSet(null, HystrixConcurrencyStrategyDefault.getInstance());
// we don't return from here but call get() again in case of thread-race so the winner will always get returned
} else {
// we received an implementation from Archaius so use it
concurrencyStrategy.compareAndSet(null, (HystrixConcurrencyStrategy) impl);
}
}
return concurrencyStrategy.get();
}
/**
* Register a {@link HystrixConcurrencyStrategy} implementation as a global override of any injected or default implementations.
*
* @param impl
* {@link HystrixConcurrencyStrategy} implementation
* @throws IllegalStateException
* if called more than once or after the default was initialized (if usage occurs before trying to register)
*/
public void registerConcurrencyStrategy(HystrixConcurrencyStrategy impl) {
if (!concurrencyStrategy.compareAndSet(null, impl)) {
throw new IllegalStateException("Another strategy was already registered.");
}
}
/**
* Retrieve instance of {@link HystrixMetricsPublisher} to use based on order of precedence as defined in {@link HystrixPlugins} class header.
* <p>
* Override default by using {@link #registerMetricsPublisher(HystrixMetricsPublisher)} or setting property (via Archaius): <code>hystrix.plugin.HystrixMetricsPublisher.implementation</code> with the full
* classname to load.
*
* @return {@link HystrixMetricsPublisher} implementation to use
*/
public HystrixMetricsPublisher getMetricsPublisher() {
if (metricsPublisher.get() == null) {
// check for an implementation from Archaius first
Object impl = getPluginImplementation(HystrixMetricsPublisher.class);
if (impl == null) {
// nothing set via Archaius so initialize with default
metricsPublisher.compareAndSet(null, HystrixMetricsPublisherDefault.getInstance());
// we don't return from here but call get() again in case of thread-race so the winner will always get returned
} else {
// we received an implementation from Archaius so use it
metricsPublisher.compareAndSet(null, (HystrixMetricsPublisher) impl);
}
}
return metricsPublisher.get();
}
/**
* Register a {@link HystrixMetricsPublisher} implementation as a global override of any injected or default implementations.
*
* @param impl
* {@link HystrixMetricsPublisher} implementation
* @throws IllegalStateException
* if called more than once or after the default was initialized (if usage occurs before trying to register)
*/
public void registerMetricsPublisher(HystrixMetricsPublisher impl) {
if (!metricsPublisher.compareAndSet(null, impl)) {
throw new IllegalStateException("Another strategy was already registered.");
}
}
/**
* Retrieve instance of {@link HystrixPropertiesStrategy} to use based on order of precedence as defined in {@link HystrixPlugins} class header.
* <p>
* Override default by using {@link #registerPropertiesStrategy(HystrixPropertiesStrategy)} or setting property (via Archaius): <code>hystrix.plugin.HystrixPropertiesStrategy.implementation</code> with the full
* classname to load.
*
* @return {@link HystrixPropertiesStrategy} implementation to use
*/
public HystrixPropertiesStrategy getPropertiesStrategy() {
if (propertiesFactory.get() == null) {
// check for an implementation from Archaius first
Object impl = getPluginImplementation(HystrixPropertiesStrategy.class);
if (impl == null) {
// nothing set via Archaius so initialize with default
propertiesFactory.compareAndSet(null, HystrixPropertiesStrategyDefault.getInstance());
// we don't return from here but call get() again in case of thread-race so the winner will always get returned
} else {
// we received an implementation from Archaius so use it
propertiesFactory.compareAndSet(null, (HystrixPropertiesStrategy) impl);
}
}
return propertiesFactory.get();
}
/**
* Retrieves the instance of {@link HystrixDynamicProperties} to use.
* <p>
* Unlike the other plugins this plugin cannot be re-registered and is only loaded at creation
* of the {@link HystrixPlugins} singleton.
* <p>
* The order of precedence for loading implementations is:
* <ol>
* <li>System property of key: <code>hystrix.plugin.HystrixDynamicProperties.implementation</code> with the class as a value.</li>
* <li>The {@link ServiceLoader}.</li>
* <li>An implementation based on Archaius if it is found in the classpath is used.</li>
* <li>A fallback implementation based on the {@link System#getProperties()}</li>
* </ol>
* @return never <code>null</code>
*/
public HystrixDynamicProperties getDynamicProperties() {
return dynamicProperties;
}
/**
* Register a {@link HystrixPropertiesStrategy} implementation as a global override of any injected or default implementations.
*
* @param impl
* {@link HystrixPropertiesStrategy} implementation
* @throws IllegalStateException
* if called more than once or after the default was initialized (if usage occurs before trying to register)
*/
public void registerPropertiesStrategy(HystrixPropertiesStrategy impl) {
if (!propertiesFactory.compareAndSet(null, impl)) {
throw new IllegalStateException("Another strategy was already registered.");
}
}
/**
* Retrieve instance of {@link HystrixCommandExecutionHook} to use based on order of precedence as defined in {@link HystrixPlugins} class header.
* <p>
* Override default by using {@link #registerCommandExecutionHook(HystrixCommandExecutionHook)} or setting property (via Archaius): <code>hystrix.plugin.HystrixCommandExecutionHook.implementation</code> with the
* full classname to
* load.
*
* @return {@link HystrixCommandExecutionHook} implementation to use
*
* @since 1.2
*/
public HystrixCommandExecutionHook getCommandExecutionHook() {
if (commandExecutionHook.get() == null) {
// check for an implementation from Archaius first
Object impl = getPluginImplementation(HystrixCommandExecutionHook.class);
if (impl == null) {
// nothing set via Archaius so initialize with default
commandExecutionHook.compareAndSet(null, HystrixCommandExecutionHookDefault.getInstance());
// we don't return from here but call get() again in case of thread-race so the winner will always get returned
} else {
// we received an implementation from Archaius so use it
commandExecutionHook.compareAndSet(null, (HystrixCommandExecutionHook) impl);
}
}
return commandExecutionHook.get();
}
/**
* Register a {@link HystrixCommandExecutionHook} implementation as a global override of any injected or default implementations.
*
* @param impl
* {@link HystrixCommandExecutionHook} implementation
* @throws IllegalStateException
* if called more than once or after the default was initialized (if usage occurs before trying to register)
*
* @since 1.2
*/
public void registerCommandExecutionHook(HystrixCommandExecutionHook impl) {
if (!commandExecutionHook.compareAndSet(null, impl)) {
throw new IllegalStateException("Another strategy was already registered.");
}
}
private <T> T getPluginImplementation(Class<T> pluginClass) {
T p = getPluginImplementationViaProperties(pluginClass, dynamicProperties);
if (p != null) return p;
return findService(pluginClass, classLoader);
}
@SuppressWarnings("unchecked")
private static <T> T getPluginImplementationViaProperties(Class<T> pluginClass, HystrixDynamicProperties dynamicProperties) {
String classSimpleName = pluginClass.getSimpleName();
// Check Archaius for plugin class.
String propertyName = "hystrix.plugin." + classSimpleName + ".implementation";
String implementingClass = dynamicProperties.getString(propertyName, null).get();
if (implementingClass != null) {
try {
Class<?> cls = Class.forName(implementingClass);
// narrow the scope (cast) to the type we're expecting
cls = cls.asSubclass(pluginClass);
return (T) cls.newInstance();
} catch (ClassCastException e) {
throw new RuntimeException(classSimpleName + " implementation is not an instance of " + classSimpleName + ": " + implementingClass);
} catch (ClassNotFoundException e) {
throw new RuntimeException(classSimpleName + " implementation class not found: " + implementingClass, e);
} catch (InstantiationException e) {
throw new RuntimeException(classSimpleName + " implementation not able to be instantiated: " + implementingClass, e);
} catch (IllegalAccessException e) {
throw new RuntimeException(classSimpleName + " implementation not able to be accessed: " + implementingClass, e);
}
} else {
return null;
}
}
private static HystrixDynamicProperties resolveDynamicProperties(ClassLoader classLoader, LoggerSupplier logSupplier) {
HystrixDynamicProperties hp = getPluginImplementationViaProperties(HystrixDynamicProperties.class,
HystrixDynamicPropertiesSystemProperties.getInstance());
if (hp != null) {
logSupplier.getLogger().debug(
"Created HystrixDynamicProperties instance from System property named "
+ "\"hystrix.plugin.HystrixDynamicProperties.implementation\". Using class: {}",
hp.getClass().getCanonicalName());
return hp;
}
hp = findService(HystrixDynamicProperties.class, classLoader);
if (hp != null) {
logSupplier.getLogger()
.debug("Created HystrixDynamicProperties instance by loading from ServiceLoader. Using class: {}",
hp.getClass().getCanonicalName());
return hp;
}
hp = HystrixArchaiusHelper.createArchaiusDynamicProperties();
if (hp != null) {
logSupplier.getLogger().debug("Created HystrixDynamicProperties. Using class : {}",
hp.getClass().getCanonicalName());
return hp;
}
hp = HystrixDynamicPropertiesSystemProperties.getInstance();
logSupplier.getLogger().info("Using System Properties for HystrixDynamicProperties! Using class: {}",
hp.getClass().getCanonicalName());
return hp;
}
private static <T> T findService(
Class<T> spi,
ClassLoader classLoader) throws ServiceConfigurationError {
ServiceLoader<T> sl = ServiceLoader.load(spi,
classLoader);
for (T s : sl) {
if (s != null)
return s;
}
return null;
}
interface LoggerSupplier {
Logger getLogger();
}
}