Monitor visitors' codec lists, and aggregate them into a conference property. #1137
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,114 @@ | ||
| /* | ||
| * Jicofo, the Jitsi Conference Focus. | ||
| * | ||
| * Copyright @ 2015-Present 8x8, 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 org.jitsi.jicofo.util | ||
|
|
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| /** Aggregate lists of preferences coming from a large group of people, such that the resulting aggregated | ||
| * list consists of preference items supported by everyone, and in a rough consensus of preference order. | ||
| * | ||
| * The intended use case is maintaining the list of supported codecs for conference visitors. | ||
| * | ||
| * Preferences are aggregated using the Borda count; this isn't theoretically optimal, but it's computationally cheap. | ||
| */ | ||
| class PreferenceAggregator( | ||
| private val onChanged: (List<String>) -> Unit | ||
| ) { | ||
| private val lock = Any() | ||
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| var aggregate: List<String> = emptyList() | ||
| private set | ||
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| var count = 0 | ||
| private set | ||
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| private val values = mutableMapOf<String, ValueInfo>() | ||
|
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| /** | ||
| * Add a preference to the aggregator. | ||
| */ | ||
| fun addPreference(prefs: List<String>) { | ||
| synchronized(lock) { | ||
| count++ | ||
| prefs.forEachIndexed { index, element -> | ||
| val info = values.computeIfAbsent(element) { ValueInfo() } | ||
| info.count++ | ||
| info.rankAggregate += index | ||
| } | ||
| updateAggregate() | ||
| } | ||
| } | ||
|
|
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| /** | ||
| * Remove a preference from the aggregator. | ||
| */ | ||
| fun removePreference(prefs: List<String>) { | ||
| synchronized(lock) { | ||
| count-- | ||
| check(count >= 0) { | ||
|
There was a problem hiding this comment. This could also be force to fail by sending initial presence with no codecs, then updating with some codecs, then leaving repeatedly |
||
| "Preference count $count should not be negative" | ||
| } | ||
| prefs.forEachIndexed { index, element -> | ||
| val info = values[element] | ||
| check(info != null) { | ||
| "Preference info for $element should exist when preferences are being removed" | ||
| } | ||
| info.count-- | ||
| check(info.count >= 0) { | ||
| "Preference count for $element ${info.count} should not be negative" | ||
| } | ||
| info.rankAggregate -= index | ||
| check(info.rankAggregate >= 0) { | ||
| "Preference rank aggregate for $element ${info.rankAggregate} should not be negative" | ||
| } | ||
| if (info.count == 0) { | ||
| check(info.rankAggregate == 0) { | ||
| "Preference rank aggregate for $element ${info.rankAggregate} should be zero " + | ||
| "when preference count is 0" | ||
| } | ||
| values.remove(element) | ||
| } | ||
| } | ||
| updateAggregate() | ||
| } | ||
| } | ||
|
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| fun reset() { | ||
| synchronized(lock) { | ||
| aggregate = emptyList() | ||
| count = 0 | ||
| values.clear() | ||
| } | ||
| } | ||
|
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| private fun updateAggregate() { | ||
| val newAggregate = values.asSequence() | ||
| .filter { it.value.count == count } | ||
| .sortedBy { it.value.rankAggregate } | ||
| .map { it.key } | ||
| .toList() | ||
| if (aggregate != newAggregate) { | ||
| aggregate = newAggregate | ||
| /* ?? Do we need to drop the lock before calling this? */ | ||
| onChanged(aggregate) | ||
| } | ||
| } | ||
|
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| private class ValueInfo { | ||
| var count = 0 | ||
| var rankAggregate = 0 | ||
| } | ||
| } | ||
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We allow codecs to change from null to a non-null, so if a visitor joins with no codecs and then adds some it would mess with the count. It's a bit of a stretch, but one could trick jicofo into upgrading to av1 thus breaking video for some participants.
Maybe make
ChatRoomMemberImpl.videoCodecsalazy valand initialize it with the first presence received?Unless I misunderstand how the aggregator works