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/*
 * Copyright 2018 The gRPC Authors
 *
 * 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 io.grpc;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.VisibleForTesting;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;

/**
 * Registry of {@link LoadBalancerProvider}s.  The {@link #getDefaultRegistry default instance}
 * loads providers at runtime through the Java service provider mechanism.
 *
 * @since 1.17.0
 */
@ExperimentalApi("https://github.com/grpc/grpc-java/issues/1771")
@ThreadSafe
public final class LoadBalancerRegistry {
  private static final Logger logger = Logger.getLogger(LoadBalancerRegistry.class.getName());
  private static LoadBalancerRegistry instance;
  private static final Iterable> HARDCODED_CLASSES = getHardCodedClasses();

  private final LinkedHashSet allProviders =
      new LinkedHashSet<>();
  private final LinkedHashMap effectiveProviders =
      new LinkedHashMap<>();

  /**
   * Register a provider.
   *
   * 

If the provider's {@link LoadBalancerProvider#isAvailable isAvailable()} returns * {@code false}, this method will throw {@link IllegalArgumentException}. * *

If more than one provider with the same {@link LoadBalancerProvider#getPolicyName policy * name} are registered, the one with the highest {@link LoadBalancerProvider#getPriority * priority} will be effective. If there are more than one name-sake providers rank the highest * priority, the one registered first will be effective. */ public synchronized void register(LoadBalancerProvider provider) { addProvider(provider); refreshProviderMap(); } private synchronized void addProvider(LoadBalancerProvider provider) { checkArgument(provider.isAvailable(), "isAvailable() returned false"); allProviders.add(provider); } /** * Deregisters a provider. No-op if the provider is not in the registry. If there are more * than one providers with the same policy name as the deregistered one in the registry, one * of them will become the effective provider for that policy, per the rule documented in {@link * #register}. * * @param provider the provider that was added to the register via {@link #register}. */ public synchronized void deregister(LoadBalancerProvider provider) { allProviders.remove(provider); refreshProviderMap(); } private synchronized void refreshProviderMap() { effectiveProviders.clear(); for (LoadBalancerProvider provider : allProviders) { String policy = provider.getPolicyName(); LoadBalancerProvider existing = effectiveProviders.get(policy); if (existing == null || existing.getPriority() < provider.getPriority()) { effectiveProviders.put(policy, provider); } } } /** * Returns the default registry that loads providers via the Java service loader mechanism. */ public static synchronized LoadBalancerRegistry getDefaultRegistry() { if (instance == null) { List providerList = ServiceProviders.loadAll( LoadBalancerProvider.class, HARDCODED_CLASSES, LoadBalancerProvider.class.getClassLoader(), new LoadBalancerPriorityAccessor()); instance = new LoadBalancerRegistry(); for (LoadBalancerProvider provider : providerList) { logger.fine("Service loader found " + provider); instance.addProvider(provider); } instance.refreshProviderMap(); } return instance; } /** * Returns the effective provider for the given load-balancing policy, or {@code null} if no * suitable provider can be found. Each provider declares its policy name via {@link * LoadBalancerProvider#getPolicyName}. */ @Nullable public synchronized LoadBalancerProvider getProvider(String policy) { return effectiveProviders.get(checkNotNull(policy, "policy")); } /** * Returns effective providers in a new map. */ @VisibleForTesting synchronized Map providers() { return new LinkedHashMap<>(effectiveProviders); } @VisibleForTesting static List> getHardCodedClasses() { // Class.forName(String) is used to remove the need for ProGuard configuration. Note that // ProGuard does not detect usages of Class.forName(String, boolean, ClassLoader): // https://sourceforge.net/p/proguard/bugs/418/ ArrayList> list = new ArrayList<>(); try { list.add(Class.forName("io.grpc.internal.PickFirstLoadBalancerProvider")); } catch (ClassNotFoundException e) { logger.log(Level.WARNING, "Unable to find pick-first LoadBalancer", e); } try { list.add(Class.forName("io.grpc.util.SecretRoundRobinLoadBalancerProvider$Provider")); } catch (ClassNotFoundException e) { // Since hard-coded list is only used in Android environment, and we don't expect round-robin // to be actually used there, we log it as a lower level. logger.log(Level.FINE, "Unable to find round-robin LoadBalancer", e); } return Collections.unmodifiableList(list); } private static final class LoadBalancerPriorityAccessor implements ServiceProviders.PriorityAccessor { LoadBalancerPriorityAccessor() {} @Override public boolean isAvailable(LoadBalancerProvider provider) { return provider.isAvailable(); } @Override public int getPriority(LoadBalancerProvider provider) { return provider.getPriority(); } } }





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