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/*
* Copyright (C) 2020 ActiveJ LLC.
*
* 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.activej.fs.cluster;
import io.activej.async.callback.Callback;
import io.activej.fs.ActiveFs;
import org.jetbrains.annotations.Nullable;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
/**
* A service that allows to discover actual {@link ActiveFs} partitions in a cluster
*/
public interface DiscoveryService {
/**
* Discovers actual {@link ActiveFs} partitions in a cluster
*
* A previous partitions are supplied. Whenever a set of actual partitions changes
* and is not the same as previous partitions, a callback will be completed
* with new partitions as a result. A callback will also be completed if an error occurs.
*
* If there are multiple {@code discover(...)} calls, the callbacks should be completed
* in the order in which they were passed to the method
*
* @param previous previous partitions
* @param cb callback to be completed when a set of actual partitions in a cluster changes
* or an error occurs
*/
void discover(@Nullable Map previous, Callback> cb);
/**
* A {@code DiscoveryService} that consists of given partitions that never change
*
* @param partitions constant {@link ActiveFs} partitions
* @return a constant discovery service
*/
static DiscoveryService constant(Map partitions) {
Map constant = Collections.unmodifiableMap(new HashMap<>(partitions));
return (previous, cb) -> {
if (!constant.equals(previous)) {
cb.accept(constant, null);
}
};
}
}