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Merge pull request #10867 from smoogipoo/refactor-user-request
Refactor user caching to improve readability and fix threadsafety issues
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@ -1,7 +1,6 @@
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// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
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// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
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// See the LICENCE file in the repository root for full licence text.
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// See the LICENCE file in the repository root for full licence text.
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using System;
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using System.Collections.Generic;
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using System.Collections.Generic;
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using System.Linq;
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using System.Linq;
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using System.Threading;
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using System.Threading;
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@ -15,103 +14,93 @@ namespace osu.Game.Database
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{
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{
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public class UserLookupCache : MemoryCachingComponent<int, User>
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public class UserLookupCache : MemoryCachingComponent<int, User>
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{
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{
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private readonly HashSet<int> nextTaskIDs = new HashSet<int>();
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[Resolved]
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[Resolved]
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private IAPIProvider api { get; set; }
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private IAPIProvider api { get; set; }
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private readonly object taskAssignmentLock = new object();
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private Task<List<User>> pendingRequest;
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/// <summary>
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/// Whether <see cref="pendingRequest"/> has already grabbed its IDs.
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/// </summary>
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private bool pendingRequestConsumedIDs;
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public Task<User> GetUserAsync(int userId, CancellationToken token = default) => GetAsync(userId, token);
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public Task<User> GetUserAsync(int userId, CancellationToken token = default) => GetAsync(userId, token);
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protected override async Task<User> ComputeValueAsync(int lookup, CancellationToken token = default)
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protected override async Task<User> ComputeValueAsync(int lookup, CancellationToken token = default)
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{
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=> await queryUser(lookup);
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var users = await getQueryTaskForUser(lookup);
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return users.FirstOrDefault(u => u.Id == lookup);
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}
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/// <summary>
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private readonly Queue<(int id, TaskCompletionSource<User>)> pendingUserTasks = new Queue<(int, TaskCompletionSource<User>)>();
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/// Return the task responsible for fetching the provided user.
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private Task pendingRequestTask;
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/// This may be part of a larger batch lookup to reduce web requests.
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private readonly object taskAssignmentLock = new object();
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/// </summary>
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/// <param name="userId">The user to lookup.</param>
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private Task<User> queryUser(int userId)
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/// <returns>The task responsible for the lookup.</returns>
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private Task<List<User>> getQueryTaskForUser(int userId)
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{
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{
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lock (taskAssignmentLock)
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lock (taskAssignmentLock)
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{
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{
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nextTaskIDs.Add(userId);
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var tcs = new TaskCompletionSource<User>();
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// if there's a pending request which hasn't been started yet (and is not yet full), we can wait on it.
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// Add to the queue.
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if (pendingRequest != null && !pendingRequestConsumedIDs && nextTaskIDs.Count < 50)
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pendingUserTasks.Enqueue((userId, tcs));
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return pendingRequest;
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return queueNextTask(nextLookup);
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// Create a request task if there's not already one.
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if (pendingRequestTask == null)
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createNewTask();
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return tcs.Task;
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}
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}
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}
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List<User> nextLookup()
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private void performLookup()
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{
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// contains at most 50 unique user IDs from userTasks, which is used to perform the lookup.
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var userTasks = new Dictionary<int, List<TaskCompletionSource<User>>>();
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// Grab at most 50 unique user IDs from the queue.
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lock (taskAssignmentLock)
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{
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{
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int[] lookupItems;
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while (pendingUserTasks.Count > 0 && userTasks.Count < 50)
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lock (taskAssignmentLock)
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{
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{
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pendingRequestConsumedIDs = true;
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(int id, TaskCompletionSource<User> task) next = pendingUserTasks.Dequeue();
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lookupItems = nextTaskIDs.ToArray();
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nextTaskIDs.Clear();
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if (lookupItems.Length == 0)
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// Perform a secondary check for existence, in case the user was queried in a previous batch.
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if (CheckExists(next.id, out var existing))
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next.task.SetResult(existing);
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else
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{
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{
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queueNextTask(null);
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if (userTasks.TryGetValue(next.id, out var tasks))
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return new List<User>();
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tasks.Add(next.task);
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else
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userTasks[next.id] = new List<TaskCompletionSource<User>> { next.task };
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}
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}
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}
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}
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var request = new GetUsersRequest(lookupItems);
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// rather than queueing, we maintain our own single-threaded request stream.
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api.Perform(request);
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return request.Result?.Users;
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}
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}
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}
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/// <summary>
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// Query the users.
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/// Queues new work at the end of the current work tasks.
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var request = new GetUsersRequest(userTasks.Keys.ToArray());
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/// Ensures the provided work is eventually run.
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/// </summary>
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// rather than queueing, we maintain our own single-threaded request stream.
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/// <param name="work">The work to run. Can be null to signify the end of available work.</param>
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api.Perform(request);
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/// <returns>The task tracking this work.</returns>
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private Task<List<User>> queueNextTask(Func<List<User>> work)
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// Create a new request task if there's still more users to query.
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{
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lock (taskAssignmentLock)
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lock (taskAssignmentLock)
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{
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{
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if (work == null)
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pendingRequestTask = null;
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{
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if (pendingUserTasks.Count > 0)
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pendingRequest = null;
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createNewTask();
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pendingRequestConsumedIDs = false;
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}
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}
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else if (pendingRequest == null)
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{
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// special case for the first request ever.
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pendingRequest = Task.Run(work);
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pendingRequestConsumedIDs = false;
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}
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else
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{
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// append the new request on to the last to be executed.
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pendingRequest = pendingRequest.ContinueWith(_ => work());
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pendingRequestConsumedIDs = false;
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}
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return pendingRequest;
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foreach (var user in request.Result.Users)
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{
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if (userTasks.TryGetValue(user.Id, out var tasks))
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{
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foreach (var task in tasks)
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task.SetResult(user);
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userTasks.Remove(user.Id);
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}
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}
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// if any tasks remain which were not satisfied, return null.
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foreach (var tasks in userTasks.Values)
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{
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foreach (var task in tasks)
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task.SetResult(null);
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}
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}
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}
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}
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private void createNewTask() => pendingRequestTask = Task.Run(performLookup);
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}
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}
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}
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}
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