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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 com.google.common.base.MoreObjects;
import io.grpc.NameResolver.ConfigOrError;
import java.util.Map;

/**
 * Provider of {@link LoadBalancer}s.  Each provider is bounded to a load-balancing policy name.
 *
 * 

Implementations can be automatically discovered by gRPC via Java's SPI mechanism. For * automatic discovery, the implementation must have a zero-argument constructor and include * a resource named {@code META-INF/services/io.grpc.LoadBalancerProvider} in their JAR. The * file's contents should be the implementation's class name. Implementations that need arguments in * their constructor can be manually registered by {@link LoadBalancerRegistry#register}. * *

Implementations should not throw. If they do, it may interrupt class loading. If * exceptions may reasonably occur for implementation-specific reasons, implementations should * generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}. * * @since 1.17.0 */ @ExperimentalApi("https://github.com/grpc/grpc-java/issues/1771") public abstract class LoadBalancerProvider extends LoadBalancer.Factory { /** * A sentinel value indicating that service config is not supported. This can be used to * indicate that parsing of the service config is neither right nor wrong, but doesn't have * any meaning. */ private static final ConfigOrError UNKNOWN_CONFIG = ConfigOrError.fromConfig(new UnknownConfig()); /** * Whether this provider is available for use, taking the current environment into consideration. * If {@code false}, {@link #newLoadBalancer} is not safe to be called. */ public abstract boolean isAvailable(); /** * A priority, from 0 to 10 that this provider should be used, taking the current environment into * consideration. 5 should be considered the default, and then tweaked based on environment * detection. A priority of 0 does not imply that the provider wouldn't work; just that it should * be last in line. */ public abstract int getPriority(); /** * Returns the load-balancing policy name associated with this provider, which makes it selectable * via {@link LoadBalancerRegistry#getProvider}. This is called only when the class is loaded. It * shouldn't change, and there is no point doing so. * *

The policy name should consist of only lower case letters letters, underscore and digits, * and can only start with letters. */ public abstract String getPolicyName(); /** * Parses the config for the Load Balancing policy unpacked from the service config. This will * return a {@link ConfigOrError} which contains either the successfully parsed config, or the * {@link Status} representing the failure to parse. Implementations are expected to not throw * exceptions but return a Status representing the failure. If successful, the load balancing * policy config should be immutable. * * @param rawLoadBalancingPolicyConfig The {@link Map} representation of the load balancing * policy choice. * @return a tuple of the fully parsed and validated balancer configuration, else the Status. * @since 1.20.0 * @see * A24-lb-policy-config.md */ public ConfigOrError parseLoadBalancingPolicyConfig(Map rawLoadBalancingPolicyConfig) { return UNKNOWN_CONFIG; } @Override public final String toString() { return MoreObjects.toStringHelper(this) .add("policy", getPolicyName()) .add("priority", getPriority()) .add("available", isAvailable()) .toString(); } /** * Uses identity equality. */ @Override public final boolean equals(Object other) { return this == other; } @Override public final int hashCode() { return super.hashCode(); } private static final class UnknownConfig { UnknownConfig() {} @Override public String toString() { return "service config is unused"; } } }





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