| | | 1 | | using Microsoft.Extensions.Logging; |
| | | 2 | | |
| | | 3 | | namespace AsyncResponse; |
| | | 4 | | |
| | | 5 | | /// <summary> |
| | | 6 | | /// Owns the per-channel <see cref="ChannelSerialExecutor"/> instances for a response channel and |
| | | 7 | | /// coordinates their lifecycle so that, for any one channel key, work is never enqueued onto an |
| | | 8 | | /// executor that is concurrently being retired — which would silently drop the message — and at |
| | | 9 | | /// most one <em>live</em> executor exists per channel at a time. |
| | | 10 | | /// <para> |
| | | 11 | | /// The coordination is a single lock guarding the map. <see cref="EnqueueAsync"/> reserves the live |
| | | 12 | | /// executor under that lock, then waits for bounded queue capacity outside it. Retirement closes |
| | | 13 | | /// admission, waits for those reservations, drains the executor, and only then lets a new executor |
| | | 14 | | /// be created. Disposal runs outside the lock. |
| | | 15 | | /// </para> |
| | | 16 | | /// <para> |
| | | 17 | | /// This replaces an earlier <c>ConcurrentDictionary</c> + fire-and-forget <c>Task.Run(remove)</c> |
| | | 18 | | /// scheme in which a new waiter reusing a correlation id mid-drain could observe a second executor |
| | | 19 | | /// for the same channel, briefly violating the per-channel ordering guarantee. |
| | | 20 | | /// </para> |
| | | 21 | | /// </summary> |
| | | 22 | | internal sealed class SerialExecutorRegistry(ILogger _logger) |
| | | 23 | | { |
| | | 24 | | // How long a retired channel's tombstone blocks executor re-creation. Long enough to outlive |
| | | 25 | | // any enqueue that was already in flight when cleanup retired the executor, short enough that |
| | | 26 | | // an unpruned tombstone only ever delays a reused correlation id briefly. |
| | | 27 | | internal static readonly TimeSpan TombstoneLifetime = TimeSpan.FromSeconds(30); |
| | | 28 | | |
| | | 29 | | private readonly Dictionary<string, ExecutorEntry> _executors = new(StringComparer.Ordinal); |
| | | 30 | | private readonly Dictionary<string, DateTime> _tombstones = new(StringComparer.Ordinal); |
| | | 31 | | private readonly Dictionary<string, int> _registrations = new(StringComparer.Ordinal); |
| | | 32 | | private readonly object _gate = new(); |
| | | 33 | | |
| | | 34 | | /// <summary> |
| | | 35 | | /// Records a live subscription for <paramref name="channel"/>. While any subscription is |
| | | 36 | | /// registered, retirement tombstones do not drop work — a retired executor is legitimately |
| | | 37 | | /// recreated, and the remaining subscription's own cleanup retires it again (no leak). |
| | | 38 | | /// </summary> |
| | | 39 | | public void OnSubscriptionRegistered(string channel) |
| | | 40 | | { |
| | | 41 | | ArgumentException.ThrowIfNullOrWhiteSpace(channel); |
| | | 42 | | |
| | | 43 | | lock (_gate) |
| | | 44 | | { |
| | | 45 | | _registrations[channel] = _registrations.TryGetValue(channel, out var count) ? count + 1 : 1; |
| | | 46 | | _tombstones.Remove(channel); |
| | | 47 | | } |
| | | 48 | | } |
| | | 49 | | |
| | | 50 | | /// <summary>Records that a subscription for <paramref name="channel"/> is gone.</summary> |
| | | 51 | | public void OnSubscriptionRetired(string channel) |
| | | 52 | | { |
| | | 53 | | ArgumentException.ThrowIfNullOrWhiteSpace(channel); |
| | | 54 | | |
| | | 55 | | lock (_gate) |
| | | 56 | | { |
| | | 57 | | if (!_registrations.TryGetValue(channel, out var count)) |
| | | 58 | | return; |
| | | 59 | | |
| | | 60 | | if (count <= 1) |
| | | 61 | | _registrations.Remove(channel); |
| | | 62 | | else |
| | | 63 | | _registrations[channel] = count - 1; |
| | | 64 | | } |
| | | 65 | | } |
| | | 66 | | |
| | | 67 | | /// <summary> |
| | | 68 | | /// Asynchronously enqueues work, applying bounded per-channel backpressure. Returns <c>true</c> |
| | | 69 | | /// once the work is accepted by a live executor; <c>false</c> when it was suppressed by a |
| | | 70 | | /// tombstone (the executor was retired with no registration left — every dispatch it ever |
| | | 71 | | /// admitted has fully completed, so a caller draining before disposal knows nothing is in |
| | | 72 | | /// flight). |
| | | 73 | | /// </summary> |
| | | 74 | | public async ValueTask<bool> EnqueueAsync(string channel, Func<Task> work, CancellationToken cancellationToken = def |
| | | 75 | | { |
| | | 76 | | ArgumentException.ThrowIfNullOrWhiteSpace(channel); |
| | | 77 | | ArgumentNullException.ThrowIfNull(work); |
| | | 78 | | |
| | | 79 | | while (true) |
| | | 80 | | { |
| | | 81 | | ExecutorEntry? entry = null; |
| | | 82 | | Task? retirement = null; |
| | | 83 | | lock (_gate) |
| | | 84 | | { |
| | | 85 | | if (!_executors.TryGetValue(channel, out var current)) |
| | | 86 | | { |
| | | 87 | | // A tombstoned channel was retired and no subscription is registered anymore: |
| | | 88 | | // recreating an executor here (typically for an enqueue that was already in |
| | | 89 | | // flight when cleanup ran) would leak it — nothing retires it again — and the |
| | | 90 | | // work item would no-op anyway because the subscriptions are gone. Drop it. |
| | | 91 | | // With a subscription still registered the recreate is legitimate (its own |
| | | 92 | | // cleanup retires the new executor), so the tombstone does not apply. |
| | | 93 | | if (!_registrations.ContainsKey(channel) && IsTombstonedUnderLock(channel)) |
| | | 94 | | { |
| | | 95 | | // Deliberate, but never silent: if this fires for a live waiter, its channel |
| | | 96 | | // registered the subscription only after the transport began delivering. |
| | | 97 | | _logger.LogWarning( |
| | | 98 | | "Suppressed a delivery for channel {Channel}: the channel is tombstoned and has no registere |
| | | 99 | | channel); |
| | | 100 | | return false; |
| | | 101 | | } |
| | | 102 | | |
| | | 103 | | current = new ExecutorEntry(new ChannelSerialExecutor(_logger, channel)); |
| | | 104 | | _executors[channel] = current; |
| | | 105 | | } |
| | | 106 | | |
| | | 107 | | if (current.Retiring) |
| | | 108 | | retirement = current.Retired.Task; |
| | | 109 | | else |
| | | 110 | | { |
| | | 111 | | current.InFlightEnqueues++; |
| | | 112 | | entry = current; |
| | | 113 | | } |
| | | 114 | | } |
| | | 115 | | |
| | | 116 | | if (entry is null) |
| | | 117 | | { |
| | | 118 | | await retirement!.WaitAsync(cancellationToken).ConfigureAwait(false); |
| | | 119 | | continue; |
| | | 120 | | } |
| | | 121 | | |
| | | 122 | | bool accepted; |
| | | 123 | | try |
| | | 124 | | { |
| | | 125 | | accepted = await entry.Executor.Enqueue(work, cancellationToken).ConfigureAwait(false); |
| | | 126 | | } |
| | | 127 | | finally |
| | | 128 | | { |
| | | 129 | | TaskCompletionSource? enqueuesDrained = null; |
| | | 130 | | lock (_gate) |
| | | 131 | | { |
| | | 132 | | entry.InFlightEnqueues--; |
| | | 133 | | if (entry.Retiring && entry.InFlightEnqueues == 0) |
| | | 134 | | enqueuesDrained = entry.EnqueuesDrained; |
| | | 135 | | } |
| | | 136 | | |
| | | 137 | | enqueuesDrained?.TrySetResult(); |
| | | 138 | | } |
| | | 139 | | |
| | | 140 | | if (accepted) |
| | | 141 | | return true; |
| | | 142 | | } |
| | | 143 | | } |
| | | 144 | | |
| | | 145 | | /// <summary> |
| | | 146 | | /// Retires the channel's serial executor (if present), draining its queued work. Safe to call |
| | | 147 | | /// concurrently with <see cref="EnqueueAsync"/>: admitted enqueues finish against the retiring |
| | | 148 | | /// executor, while later enqueues wait until it is fully drained before creating a replacement. |
| | | 149 | | /// </summary> |
| | | 150 | | public async ValueTask RemoveAsync(string channel) |
| | | 151 | | { |
| | | 152 | | ArgumentException.ThrowIfNullOrWhiteSpace(channel); |
| | | 153 | | |
| | | 154 | | ExecutorEntry? entry; |
| | | 155 | | Task waitForEnqueues; |
| | | 156 | | var ownsRetirement = false; |
| | | 157 | | lock (_gate) |
| | | 158 | | { |
| | | 159 | | if (!_executors.TryGetValue(channel, out entry)) |
| | | 160 | | return; |
| | | 161 | | |
| | | 162 | | if (entry.Retiring) |
| | | 163 | | { |
| | | 164 | | waitForEnqueues = entry.Retired.Task; |
| | | 165 | | } |
| | | 166 | | else |
| | | 167 | | { |
| | | 168 | | entry.Retiring = true; |
| | | 169 | | ownsRetirement = true; |
| | | 170 | | if (entry.InFlightEnqueues == 0) |
| | | 171 | | { |
| | | 172 | | waitForEnqueues = Task.CompletedTask; |
| | | 173 | | } |
| | | 174 | | else |
| | | 175 | | { |
| | | 176 | | entry.EnqueuesDrained = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously) |
| | | 177 | | waitForEnqueues = entry.EnqueuesDrained.Task; |
| | | 178 | | } |
| | | 179 | | } |
| | | 180 | | } |
| | | 181 | | |
| | | 182 | | if (!ownsRetirement) |
| | | 183 | | { |
| | | 184 | | await waitForEnqueues.ConfigureAwait(false); |
| | | 185 | | return; |
| | | 186 | | } |
| | | 187 | | |
| | | 188 | | try |
| | | 189 | | { |
| | | 190 | | await waitForEnqueues.ConfigureAwait(false); |
| | | 191 | | await entry.Executor.DisposeAsync().ConfigureAwait(false); |
| | | 192 | | } |
| | | 193 | | finally |
| | | 194 | | { |
| | | 195 | | lock (_gate) |
| | | 196 | | { |
| | | 197 | | if (_executors.TryGetValue(channel, out var current) && ReferenceEquals(current, entry)) |
| | | 198 | | _executors.Remove(channel); |
| | | 199 | | |
| | | 200 | | // Tombstone the retired channel so an enqueue that raced this retirement cannot |
| | | 201 | | // recreate a leaked executor; ClearTombstone lifts it the moment a new |
| | | 202 | | // subscription legitimately reuses the channel. |
| | | 203 | | _tombstones[channel] = DateTime.UtcNow + TombstoneLifetime; |
| | | 204 | | PruneTombstonesUnderLock(); |
| | | 205 | | } |
| | | 206 | | |
| | | 207 | | entry.Retired.TrySetResult(); |
| | | 208 | | } |
| | | 209 | | } |
| | | 210 | | |
| | | 211 | | private bool IsTombstonedUnderLock(string channel) |
| | | 212 | | { |
| | | 213 | | if (!_tombstones.TryGetValue(channel, out var expiresAtUtc)) |
| | | 214 | | return false; |
| | | 215 | | |
| | | 216 | | if (expiresAtUtc > DateTime.UtcNow) |
| | | 217 | | return true; |
| | | 218 | | |
| | | 219 | | _tombstones.Remove(channel); |
| | | 220 | | return false; |
| | | 221 | | } |
| | | 222 | | |
| | | 223 | | private void PruneTombstonesUnderLock() |
| | | 224 | | { |
| | | 225 | | if (_tombstones.Count == 0) |
| | | 226 | | return; |
| | | 227 | | |
| | | 228 | | var now = DateTime.UtcNow; |
| | | 229 | | List<string>? expired = null; |
| | | 230 | | foreach (var (channel, expiresAtUtc) in _tombstones) |
| | | 231 | | { |
| | | 232 | | if (expiresAtUtc <= now) |
| | | 233 | | (expired ??= []).Add(channel); |
| | | 234 | | } |
| | | 235 | | |
| | | 236 | | if (expired is null) |
| | | 237 | | return; |
| | | 238 | | |
| | | 239 | | foreach (var channel in expired) |
| | | 240 | | _tombstones.Remove(channel); |
| | | 241 | | } |
| | | 242 | | |
| | 3 | 243 | | private sealed class ExecutorEntry(ChannelSerialExecutor executor) |
| | | 244 | | { |
| | 3 | 245 | | public ChannelSerialExecutor Executor { get; } = executor; |
| | 3 | 246 | | public TaskCompletionSource Retired { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously); |
| | | 247 | | public TaskCompletionSource? EnqueuesDrained { get; set; } |
| | | 248 | | public int InFlightEnqueues { get; set; } |
| | | 249 | | public bool Retiring { get; set; } |
| | | 250 | | } |
| | | 251 | | } |