Add BeatmapLookupCache

osu.Game/Database/BeatmapLookupCache.cs

@@ -0,0 +1,143 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using JetBrains.Annotations;
+using osu.Framework.Allocation;
+using osu.Game.Online.API;
+using osu.Game.Online.API.Requests;
+using osu.Game.Online.API.Requests.Responses;
+
+namespace osu.Game.Database
+{
+    // This class is based on `UserLookupCache` which is well tested.
+    // If modifications are to be made here, a base abstract implementation should likely be created and shared between the two.
+    public class BeatmapLookupCache : MemoryCachingComponent<int, APIBeatmap>
+    {
+        [Resolved]
+        private IAPIProvider api { get; set; }
+
+        /// <summary>
+        /// Perform an API lookup on the specified beatmap, populating a <see cref="APIBeatmap"/> model.
+        /// </summary>
+        /// <param name="beatmapId">The beatmap to lookup.</param>
+        /// <param name="token">An optional cancellation token.</param>
+        /// <returns>The populated beatmap, or null if the beatmap does not exist or the request could not be satisfied.</returns>
+        [ItemCanBeNull]
+        public Task<APIBeatmap> GetBeatmapAsync(int beatmapId, CancellationToken token = default) => GetAsync(beatmapId, token);
+
+        /// <summary>
+        /// Perform an API lookup on the specified beatmaps, populating a <see cref="APIBeatmap"/> model.
+        /// </summary>
+        /// <param name="beatmapIds">The beatmaps to lookup.</param>
+        /// <param name="token">An optional cancellation token.</param>
+        /// <returns>The populated beatmaps. May include null results for failed retrievals.</returns>
+        public Task<APIBeatmap[]> GetBeatmapsAsync(int[] beatmapIds, CancellationToken token = default)
+        {
+            var beatmapLookupTasks = new List<Task<APIBeatmap>>();
+
+            foreach (int u in beatmapIds)
+            {
+                beatmapLookupTasks.Add(GetBeatmapAsync(u, token).ContinueWith(task =>
+                {
+                    if (!task.IsCompletedSuccessfully)
+                        return null;
+
+                    return task.Result;
+                }, token));
+            }
+
+            return Task.WhenAll(beatmapLookupTasks);
+        }
+
+        protected override async Task<APIBeatmap> ComputeValueAsync(int lookup, CancellationToken token = default)
+            => await queryBeatmap(lookup).ConfigureAwait(false);
+
+        private readonly Queue<(int id, TaskCompletionSource<APIBeatmap>)> pendingBeatmapTasks = new Queue<(int, TaskCompletionSource<APIBeatmap>)>();
+        private Task pendingRequestTask;
+        private readonly object taskAssignmentLock = new object();
+
+        private Task<APIBeatmap> queryBeatmap(int beatmapId)
+        {
+            lock (taskAssignmentLock)
+            {
+                var tcs = new TaskCompletionSource<APIBeatmap>();
+
+                // Add to the queue.
+                pendingBeatmapTasks.Enqueue((beatmapId, tcs));
+
+                // Create a request task if there's not already one.
+                if (pendingRequestTask == null)
+                    createNewTask();
+
+                return tcs.Task;
+            }
+        }
+
+        private void performLookup()
+        {
+            // contains at most 50 unique beatmap IDs from beatmapTasks, which is used to perform the lookup.
+            var beatmapTasks = new Dictionary<int, List<TaskCompletionSource<APIBeatmap>>>();
+
+            // Grab at most 50 unique beatmap IDs from the queue.
+            lock (taskAssignmentLock)
+            {
+                while (pendingBeatmapTasks.Count > 0 && beatmapTasks.Count < 1)
+                {
+                    (int id, TaskCompletionSource<APIBeatmap> task) next = pendingBeatmapTasks.Dequeue();
+
+                    // Perform a secondary check for existence, in case the beatmap was queried in a previous batch.
+                    if (CheckExists(next.id, out var existing))
+                        next.task.SetResult(existing);
+                    else
+                    {
+                        if (beatmapTasks.TryGetValue(next.id, out var tasks))
+                            tasks.Add(next.task);
+                        else
+                            beatmapTasks[next.id] = new List<TaskCompletionSource<APIBeatmap>> { next.task };
+                    }
+                }
+            }
+
+            // Query the beatmaps.
+            var request = new GetBeatmapRequest(new APIBeatmap { OnlineID = beatmapTasks.Keys.First() });
+
+            // rather than queueing, we maintain our own single-threaded request stream.
+            // todo: we probably want retry logic here.
+            api.Perform(request);
+
+            // Create a new request task if there's still more beatmaps to query.
+            lock (taskAssignmentLock)
+            {
+                pendingRequestTask = null;
+                if (pendingBeatmapTasks.Count > 0)
+                    createNewTask();
+            }
+
+            List<APIBeatmap> foundBeatmaps = new List<APIBeatmap> { request.Response };
+
+            foreach (var beatmap in foundBeatmaps)
+            {
+                if (beatmapTasks.TryGetValue(beatmap.OnlineID, out var tasks))
+                {
+                    foreach (var task in tasks)
+                        task.SetResult(beatmap);
+
+                    beatmapTasks.Remove(beatmap.OnlineID);
+                }
+            }
+
+            // if any tasks remain which were not satisfied, return null.
+            foreach (var tasks in beatmapTasks.Values)
+            {
+                foreach (var task in tasks)
+                    task.SetResult(null);
+            }
+        }
+
+        private void createNewTask() => pendingRequestTask = Task.Run(performLookup);
+    }
+}