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Factor InMemoryVidIndexMap out of VidIndexMap (#1615)
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...tlin/org/wfanet/measurement/eventdataprovider/shareshuffle/v2alpha/InMemoryVidIndexMap.kt
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| // Copyright 2024 The Cross-Media Measurement 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. | ||
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| package org.wfanet.measurement.eventdataprovider.shareshuffle.v2alpha | ||
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| import com.google.common.hash.Hashing | ||
| import com.google.protobuf.ByteString | ||
| import java.nio.ByteOrder | ||
| import org.wfanet.measurement.api.v2alpha.PopulationSpec | ||
| import org.wfanet.measurement.api.v2alpha.PopulationSpecValidator | ||
| import org.wfanet.measurement.common.toByteString | ||
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| /** | ||
| * An implementation of [VidIndexMap] that holds the Map in memory. | ||
| * | ||
| * This implementation of [VidIndexMap] creates the mapping from scratch given a [PopulationSpec] | ||
| * | ||
| * Overriding the default hash function can cause incompatibilities between EDPs which can lead to | ||
| * bad measurement. The [hashFunction] is exposed only for testing. | ||
| * | ||
| * @param[populationSpec] The [PopulationSpec] to build the map for. | ||
| * @param [hashFunction] The hash function to use for hashing VIDs. | ||
| * @constructor Creates a [VidIndexMap] for the given [PopulationSpec] | ||
| * @throws [PopulationSpecValidationException] if the [populationSpec] is invalid | ||
| */ | ||
| class InMemoryVidIndexMap( | ||
| override val populationSpec: PopulationSpec, | ||
| private val hashFunction: (Long, ByteString) -> Long = Companion::hashVidToLongWithFarmHash, | ||
| ) : VidIndexMap { | ||
| // TODO(@kungfucraig): Provide a constructor that reads the vid->index map from a file. | ||
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| override val size | ||
| get() = indexMap.size.toLong() | ||
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| /** A map of a VID to its index in the [Frequency Vector]. */ | ||
| private val indexMap = hashMapOf<Long, Int>() | ||
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| /** | ||
| * A salt value to ensure the output of the hash used by the VidIndexMap is different from other | ||
| * functions that hash VIDs (e.g. the labeler). These are the first several digits of phi (the | ||
| * golden ratio) added to the date this value was created. | ||
| */ | ||
| private val salt = (1_618_033L + 20_240_417L).toByteString(ByteOrder.BIG_ENDIAN) | ||
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| /** A data class for a VID and its hash value. */ | ||
| data class VidAndHash(val vid: Long, val hash: Long) : Comparable<VidAndHash> { | ||
| override operator fun compareTo(other: VidAndHash): Int = | ||
| compareValuesBy(this, other, { it.hash }, { it.vid }) | ||
| } | ||
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| init { | ||
| PopulationSpecValidator.validateVidRangesList(populationSpec).getOrThrow() | ||
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| val hashes = mutableListOf<VidAndHash>() | ||
| for (subPop in populationSpec.subpopulationsList) { | ||
| for (range in subPop.vidRangesList) { | ||
| for (vid in range.startVid..range.endVidInclusive) { | ||
| hashes.add(VidAndHash(vid, hashFunction(vid, salt))) | ||
| } | ||
| } | ||
| } | ||
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| hashes.sortWith(compareBy<VidAndHash>() { it }) | ||
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| for ((index, vidAndHash) in hashes.withIndex()) { | ||
| indexMap[vidAndHash.vid] = index | ||
| } | ||
| } | ||
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| /** | ||
| * Returns the index in the [FrequencyVector] for the given [vid]. | ||
| * | ||
| * @throws VidNotFoundException if the [vid] does not exist in the map | ||
| */ | ||
| override operator fun get(vid: Long): Int = indexMap[vid] ?: throw VidNotFoundException(vid) | ||
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| companion object { | ||
| /** | ||
| * Hash a VID with FarmHash and return the output as a [Long] | ||
| * | ||
| * The input of the hash function is determined by converting the [vid] to a byte array with big | ||
| * endian ordering and concatenating the [salt] to it. | ||
| * | ||
| * This input is passed to farmHashFingerprint64() whose output is a byte array. | ||
| * | ||
| * The bytearray is converted to a long in little endian order, which is then returned. | ||
| * | ||
| * @param [vid] the vid to hash | ||
| * @param [salt] the value concatenated to the [vid] prior to hashing | ||
| * @returns the hash of the vid | ||
| */ | ||
| fun hashVidToLongWithFarmHash(vid: Long, salt: ByteString): Long { | ||
| val hashInput = vid.toByteString(ByteOrder.BIG_ENDIAN).concat(salt) | ||
| return Hashing.farmHashFingerprint64().hashBytes(hashInput.toByteArray()).asLong() | ||
| } | ||
| } | ||
| } |
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