Async write path (#1056)

* start work on a true async write path (no sync flush); at the moment only existing async code uses this - once stable, we can move more code to the full async path

* finish prep work before tackling subscriber lock (note: still lots of handshake options to asyncify)

* implement a background queue that represents the (necessarily ordered) subscription operations, rather than executing them synchronously (sync over async, locks, etc)

src/StackExchange.Redis/ChannelMessageQueue.cs

@@ -164,7 +164,7 @@ private async Task OnMessageSyncImpl()
             while (!Completion.IsCompleted)
             {
                 ChannelMessage next;
-                try { if (!TryRead(out next)) next = await ReadAsync().ConfigureAwait(false); }
+                try { if (!TryRead(out next)) next = await ReadAsync().ForAwait(); }
                 catch (ChannelClosedException) { break; } // expected
                 catch (Exception ex)
                 {
@@ -195,7 +195,7 @@ private async Task OnMessageAsyncImpl()
             while (!Completion.IsCompleted)
             {
                 ChannelMessage next;
-                try { if (!TryRead(out next)) next = await ReadAsync().ConfigureAwait(false); }
+                try { if (!TryRead(out next)) next = await ReadAsync().ForAwait(); }
                 catch (ChannelClosedException) { break; } // expected
                 catch (Exception ex)
                 {
@@ -206,7 +206,7 @@ private async Task OnMessageAsyncImpl()
                 try
                 {
                     var task = handler(next);
-                    if (task != null && task.Status != TaskStatus.RanToCompletion) await task.ConfigureAwait(false);
+                    if (task != null && task.Status != TaskStatus.RanToCompletion) await task.ForAwait();
                 }
                 catch { } // matches MessageCompletable
             }
@@ -229,7 +229,7 @@ internal async Task UnsubscribeAsyncImpl(Exception error = null, CommandFlags fl
             _parent = null;
             if (parent != null)
             {
-                await parent.UnsubscribeAsync(Channel, HandleMessage, flags).ConfigureAwait(false);
+                await parent.UnsubscribeAsync(Channel, HandleMessage, flags).ForAwait();
             }
             _queue.Writer.TryComplete(error);
         }

src/StackExchange.Redis/Condition.cs

 using System;
 using System.Collections.Generic;
 
+#pragma warning disable RCS1231
+
 namespace StackExchange.Redis
 {
     /// <summary>
@@ -303,6 +305,8 @@ public static Condition StringNotEqual(RedisKey key, RedisValue value)
         /// <param name="count">The number of members which sorted set must not have.</param>
         public static Condition SortedSetScoreNotExists(RedisKey key, RedisValue score, RedisValue count) => new SortedSetScoreCondition(key, score, false, count);
 
+#pragma warning restore RCS1231
+
         internal abstract void CheckCommands(CommandMap commandMap);
 
         internal abstract IEnumerable<Message> CreateMessages(int db, ResultBox resultBox);
@@ -314,12 +318,14 @@ internal sealed class ConditionProcessor : ResultProcessor<bool>
         {
             public static readonly ConditionProcessor Default = new ConditionProcessor();
 
-            public static Message CreateMessage(Condition condition, int db, CommandFlags flags, RedisCommand command, RedisKey key, RedisValue value = default(RedisValue))
+#pragma warning disable RCS1231 // Make parameter ref read-only.
+            public static Message CreateMessage(Condition condition, int db, CommandFlags flags, RedisCommand command, in RedisKey key, RedisValue value = default(RedisValue))
+#pragma warning restore RCS1231 // Make parameter ref read-only.
             {
                 return new ConditionMessage(condition, db, flags, command, key, value);
             }
 
-            public static Message CreateMessage(Condition condition, int db, CommandFlags flags, RedisCommand command, RedisKey key, RedisValue value, RedisValue value1)
+            public static Message CreateMessage(Condition condition, int db, CommandFlags flags, RedisCommand command, in RedisKey key, in RedisValue value, in RedisValue value1)
             {
                 return new ConditionMessage(condition, db, flags, command, key, value, value1);
             }
@@ -343,14 +349,14 @@ private class ConditionMessage : Message.CommandKeyBase
                 private readonly RedisValue value;
                 private readonly RedisValue value1;
 
-                public ConditionMessage(Condition condition, int db, CommandFlags flags, RedisCommand command, RedisKey key, RedisValue value)
+                public ConditionMessage(Condition condition, int db, CommandFlags flags, RedisCommand command, in RedisKey key, in RedisValue value)
                     : base(db, flags, command, key)
                 {
                     Condition = condition;
                     this.value = value; // note no assert here
                 }
 
-                public ConditionMessage(Condition condition, int db, CommandFlags flags, RedisCommand command, RedisKey key, RedisValue value, RedisValue value1)
+                public ConditionMessage(Condition condition, int db, CommandFlags flags, RedisCommand command, in RedisKey key, in RedisValue value, in RedisValue value1)
                     : this(condition, db, flags, command, key, value)
                 {
                     this.value1 = value1; // note no assert here
@@ -391,7 +397,7 @@ internal override Condition MapKeys(Func<RedisKey, RedisKey> map)
                 return new ExistsCondition(map(key), type, expectedValue, expectedResult);
             }
 
-            public ExistsCondition(RedisKey key, RedisType type, RedisValue expectedValue, bool expectedResult)
+            public ExistsCondition(in RedisKey key, RedisType type, in RedisValue expectedValue, bool expectedResult)
             {
                 if (key.IsNull) throw new ArgumentException("key");
                 this.key = key;
@@ -481,7 +487,7 @@ internal override Condition MapKeys(Func<RedisKey, RedisKey> map)
             private readonly RedisType type;
             private readonly RedisCommand cmd;
 
-            public EqualsCondition(RedisKey key, RedisType type, RedisValue memberName, bool expectedEqual, RedisValue expectedValue)
+            public EqualsCondition(in RedisKey key, RedisType type, in RedisValue memberName, bool expectedEqual, in RedisValue expectedValue)
             {
                 if (key.IsNull) throw new ArgumentException("key");
                 this.key = key;
@@ -575,7 +581,7 @@ internal override Condition MapKeys(Func<RedisKey, RedisKey> map)
             private readonly long index;
             private readonly RedisValue? expectedValue;
             private readonly RedisKey key;
-            public ListCondition(RedisKey key, long index, bool expectedResult, RedisValue? expectedValue)
+            public ListCondition(in RedisKey key, long index, bool expectedResult, in RedisValue? expectedValue)
             {
                 if (key.IsNull) throw new ArgumentException(nameof(key));
                 this.key = key;
@@ -645,7 +651,7 @@ internal override Condition MapKeys(Func<RedisKey, RedisKey> map)
             private readonly RedisType type;
             private readonly RedisCommand cmd;
 
-            public LengthCondition(RedisKey key, RedisType type, int compareToResult, long expectedLength)
+            public LengthCondition(in RedisKey key, RedisType type, int compareToResult, long expectedLength)
             {
                 if (key.IsNull) throw new ArgumentException(nameof(key));
                 this.key = key;
@@ -737,7 +743,7 @@ internal override Condition MapKeys(Func<RedisKey, RedisKey> map)
             private readonly RedisValue sortedSetScore, expectedValue;
             private readonly RedisKey key;
 
-            public SortedSetScoreCondition(RedisKey key, RedisValue sortedSetScore, bool expectedEqual, RedisValue expectedValue)
+            public SortedSetScoreCondition(in RedisKey key, in RedisValue sortedSetScore, bool expectedEqual, in RedisValue expectedValue)
             {
                 if (key.IsNull)
                 {

src/StackExchange.Redis/ConfigurationOptions.cs

@@ -291,10 +291,13 @@ public int ConnectTimeout
         /// </summary>
         public bool HighPrioritySocketThreads { get { return highPrioritySocketThreads ?? true; } set { highPrioritySocketThreads = value; } }
 
+        // Use coalesce expression.
         /// <summary>
         /// Specifies the time in seconds at which connections should be pinged to ensure validity
         /// </summary>
+#pragma warning disable RCS1128
         public int KeepAlive { get { return keepAlive.GetValueOrDefault(-1); } set { keepAlive = value; } }
+#pragma warning restore RCS1128 // Use coalesce expression.
 
         /// <summary>
         /// The password to use to authenticate with the server.
@@ -363,7 +366,9 @@ public bool PreserveAsyncOrder
         /// <summary>
         /// Specifies the time in milliseconds that the system should allow for synchronous operations (defaults to 1 second)
         /// </summary>
+#pragma warning disable RCS1128
         public int SyncTimeout { get { return syncTimeout.GetValueOrDefault(5000); } set { syncTimeout = value; } }
+#pragma warning restore RCS1128
 
         /// <summary>
         /// Tie-breaker used to choose between masters (must match the endpoint exactly)
@@ -383,7 +388,9 @@ public bool PreserveAsyncOrder
         /// <summary>
         /// Check configuration every n seconds (every minute by default)
         /// </summary>
+#pragma warning disable RCS1128
         public int ConfigCheckSeconds { get { return configCheckSeconds.GetValueOrDefault(60); } set { configCheckSeconds = value; } }
+#pragma warning restore RCS1128
 
         /// <summary>
         /// Parse the configuration from a comma-delimited configuration string

src/StackExchange.Redis/LoggingPipe.cs

@@ -71,12 +71,12 @@ private async Task CloneAsync(string path, PipeReader from, PipeWriter to)
                                 arr = new ArraySegment<byte>(tmp, 0, segment.Length);
                                 leased = true;
                             }
-                            await file.WriteAsync(arr.Array, arr.Offset, arr.Count);
-                            await file.FlushAsync();
+                            await file.WriteAsync(arr.Array, arr.Offset, arr.Count).ForAwait();
+                            await file.FlushAsync().ForAwait();
                             if (leased) ArrayPool<byte>.Shared.Return(arr.Array);
 
                             // and flush it upstream
-                            await to.WriteAsync(segment);
+                            await to.WriteAsync(segment).ForAwait();
                         }
                     }
                     from.AdvanceTo(buffer.End);

src/StackExchange.Redis/PhysicalConnection.cs

@@ -232,8 +232,6 @@ private enum ReadMode : byte
 
         public bool TransactionActive { get; internal set; }
 
-        partial void ShouldIgnoreConnect(ref bool ignore);
-
         [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2202:Do not dispose objects multiple times")]
         internal void Shutdown()
         {
@@ -275,7 +273,7 @@ public void Dispose()
 
         private async Task AwaitedFlush(ValueTask<FlushResult> flush)
         {
-            await flush;
+            await flush.ForAwait();
             _writeStatus = WriteStatus.Flushed;
             UpdateLastWriteTime();
         }
@@ -839,23 +837,50 @@ internal static int WriteRaw(Span<byte> span, long value, bool withLengthPrefix
             return WriteCrlf(span, offset);
         }
 
-        internal WriteResult FlushSync(bool throwOnFailure = false)
+        private static async ValueTask<WriteResult> FlushAsync_Awaited(PhysicalConnection connection, ValueTask<FlushResult> flush, bool throwOnFailure)
+        {
+            try
+            {
+                await flush.ForAwait();
+                connection._writeStatus = WriteStatus.Flushed;
+                connection.UpdateLastWriteTime();
+                return WriteResult.Success;
+            }
+            catch (ConnectionResetException ex) when (!throwOnFailure)
+            {
+                connection.RecordConnectionFailed(ConnectionFailureType.SocketClosed, ex);
+                return WriteResult.WriteFailure;
+            }
+        }
+
+        [Obsolete("this is an anti-pattern; work to reduce reliance on this is in progress")]
+        internal WriteResult FlushSync(bool throwOnFailure, int millisecondsTimeout)
+        {
+            var flush = FlushAsync(throwOnFailure);
+            if (!flush.IsCompletedSuccessfully)
+            {
+                // here lies the evil
+                if (!flush.AsTask().Wait(millisecondsTimeout)) throw new TimeoutException("timeout while synchronously flushing");
+            }
+            return flush.Result;
+        }
+        internal ValueTask<WriteResult> FlushAsync(bool throwOnFailure)
         {
             var tmp = _ioPipe?.Output;
-            if (tmp == null) return WriteResult.NoConnectionAvailable;
+            if (tmp == null) return new ValueTask<WriteResult>(WriteResult.NoConnectionAvailable);
             try
             {
                 _writeStatus = WriteStatus.Flushing;
                 var flush = tmp.FlushAsync();
-                if (!flush.IsCompletedSuccessfully) flush.AsTask().Wait();
+                if (!flush.IsCompletedSuccessfully) return FlushAsync_Awaited(this, flush, throwOnFailure);
                 _writeStatus = WriteStatus.Flushed;
                 UpdateLastWriteTime();
-                return WriteResult.Success;
+                return new ValueTask<WriteResult>(WriteResult.Success);
             }
             catch (ConnectionResetException ex) when (!throwOnFailure)
             {
                 RecordConnectionFailed(ConnectionFailureType.SocketClosed, ex);
-                return WriteResult.WriteFailure;
+                return new ValueTask<WriteResult>(WriteResult.WriteFailure);
             }
         }
 
@@ -874,7 +899,9 @@ private static void WriteUnifiedBlob(PipeWriter writer, byte[] value)
             }
         }
 
+#pragma warning disable RCS1231 // Make parameter ref read-only.
         private static void WriteUnifiedSpan(PipeWriter writer, ReadOnlySpan<byte> value)
+#pragma warning restore RCS1231 // Make parameter ref read-only.
         {
             // ${len}\r\n           = 3 + MaxInt32TextLen
             // {value}\r\n          = 2 + value.Length
@@ -949,8 +976,8 @@ internal void WriteSha1AsHex(byte[] value)
                 for (int i = 0; i < value.Length; i++)
                 {
                     var b = value[i];
-                    span[offset++] = ToHexNibble(value[i] >> 4);
-                    span[offset++] = ToHexNibble(value[i] & 15);
+                    span[offset++] = ToHexNibble(b >> 4);
+                    span[offset++] = ToHexNibble(b & 15);
                 }
                 span[offset++] = (byte)'\r';
                 span[offset++] = (byte)'\n';
@@ -1556,7 +1583,9 @@ private static RawResult ParseInlineProtocol(in RawResult line)
             if (!line.HasValue) return RawResult.Nil; // incomplete line
 
             int count = 0;
-            foreach (var token in line.GetInlineTokenizer()) count++;
+#pragma warning disable IDE0059
+            foreach (var _ in line.GetInlineTokenizer()) count++;
+#pragma warning restore IDE0059
             var oversized = ArrayPool<RawResult>.Shared.Rent(count);
             count = 0;
             foreach (var token in line.GetInlineTokenizer())

src/StackExchange.Redis/RedisBase.cs

@@ -54,7 +54,7 @@ internal virtual T ExecuteSync<T>(Message message, ResultProcessor<T> processor,
             return multiplexer.ExecuteSyncImpl<T>(message, processor, server);
         }
 
-        internal virtual RedisFeatures GetFeatures(RedisKey key, CommandFlags flags, out ServerEndPoint server)
+        internal virtual RedisFeatures GetFeatures(in RedisKey key, CommandFlags flags, out ServerEndPoint server)
         {
             server = multiplexer.SelectServer(RedisCommand.PING, flags, key);
             var version = server == null ? multiplexer.RawConfig.DefaultVersion : server.Version;
@@ -116,7 +116,7 @@ private ResultProcessor.TimingProcessor.TimerMessage GetTimerMessage(CommandFlag
         internal static class CursorUtils
         {
             internal const int Origin = 0, DefaultPageSize = 10;
-            internal static bool IsNil(RedisValue pattern)
+            internal static bool IsNil(in RedisValue pattern)
             {
                 if (pattern.IsNullOrEmpty) return true;
                 if (pattern.IsInteger) return false;
@@ -231,7 +231,7 @@ private enum State : byte
                     Disposed,
                 }
 
-                private void ProcessReply(ScanResult result)
+                private void ProcessReply(in ScanResult result)
                 {
                     currentCursor = nextCursor;
                     nextCursor = result.Cursor;

src/StackExchange.Redis/RedisServer.cs

@@ -7,6 +7,8 @@
 using System.Text;
 using System.Threading.Tasks;
 
+#pragma warning disable RCS1231 // Make parameter ref read-only.
+
 namespace StackExchange.Redis
 {
     internal sealed class RedisServer : RedisBase, IServer
@@ -583,7 +585,7 @@ internal override T ExecuteSync<T>(Message message, ResultProcessor<T> processor
             return base.ExecuteSync<T>(message, processor, server);
         }
 
-        internal override RedisFeatures GetFeatures(RedisKey key, CommandFlags flags, out ServerEndPoint server)
+        internal override RedisFeatures GetFeatures(in RedisKey key, CommandFlags flags, out ServerEndPoint server)
         {
             server = this.server;
             return new RedisFeatures(server.Version);
@@ -607,7 +609,9 @@ public void SlaveOf(EndPoint master, CommandFlags flags = CommandFlags.None)
             {
                 var del = Message.Create(0, CommandFlags.FireAndForget | CommandFlags.NoRedirect, RedisCommand.DEL, (RedisKey)configuration.TieBreaker);
                 del.SetInternalCall();
-                server.WriteDirectFireAndForget(del, ResultProcessor.Boolean);
+#pragma warning disable CS0618
+                server.WriteDirectFireAndForgetSync(del, ResultProcessor.Boolean);
+#pragma warning restore CS0618
             }
             ExecuteSync(slaveofMsg, ResultProcessor.DemandOK);
 
@@ -617,7 +621,9 @@ public void SlaveOf(EndPoint master, CommandFlags flags = CommandFlags.None)
             {
                 var pub = Message.Create(-1, CommandFlags.FireAndForget | CommandFlags.NoRedirect, RedisCommand.PUBLISH, (RedisValue)channel, RedisLiterals.Wildcard);
                 pub.SetInternalCall();
-                server.WriteDirectFireAndForget(pub, ResultProcessor.Int64);
+#pragma warning disable CS0618
+                server.WriteDirectFireAndForgetSync(pub, ResultProcessor.Int64);
+#pragma warning restore CS0618
             }
         }
 

src/StackExchange.Redis/RedisSubscriber.cs

@@ -127,7 +127,7 @@ internal void ResendSubscriptions(ServerEndPoint server)
             }
         }
 
-        internal bool SubscriberConnected(RedisChannel channel = default(RedisChannel))
+        internal bool SubscriberConnected(in RedisChannel channel = default(RedisChannel))
         {
             var server = GetSubscribedServer(channel);
             if (server != null) return server.IsConnected;
@@ -149,7 +149,7 @@ internal long ValidateSubscriptions()
             }
         }
 
-        private sealed class Subscription
+        internal sealed class Subscription
         {
             private Action<RedisChannel, RedisValue> _asyncHandler, _syncHandler;
             private ServerEndPoint owner;
@@ -195,25 +195,79 @@ public bool Remove(bool asAsync, Action<RedisChannel, RedisValue> value)
 
             public Task SubscribeToServer(ConnectionMultiplexer multiplexer, in RedisChannel channel, CommandFlags flags, object asyncState, bool internalCall)
             {
-                var cmd = channel.IsPatternBased ? RedisCommand.PSUBSCRIBE : RedisCommand.SUBSCRIBE;
-                var selected = multiplexer.SelectServer(cmd, flags, default(RedisKey));
+                var selected = multiplexer.SelectServer(RedisCommand.SUBSCRIBE, flags, default(RedisKey));
+                var bridge = selected?.GetBridge(ConnectionType.Subscription, true);
+                if (bridge == null) return null;
 
-                if (selected == null || Interlocked.CompareExchange(ref owner, selected, null) != null) return null;
+                // note: check we can create the message validly *before* we swap the owner over (Interlocked)
+                var state = PendingSubscriptionState.Create(channel, this, flags, true, internalCall, asyncState, selected.IsSlave);
 
-                var msg = Message.Create(-1, flags, cmd, channel);
-                if (internalCall) msg.SetInternalCall();
-                return selected.WriteDirectAsync(msg, ResultProcessor.TrackSubscriptions, asyncState);
+                if (Interlocked.CompareExchange(ref owner, selected, null) != null) return null;
+                try
+                {
+                    if (!bridge.TryEnqueueBackgroundSubscriptionWrite(state))
+                    {
+                        state.Abort();
+                        return null;
+                    }
+                    return state.Task;
+                }
+                catch
+                {
+                    // clear the owner if it is still us
+                    Interlocked.CompareExchange(ref owner, null, selected);
+                    throw;
+                }
             }
 
             public Task UnsubscribeFromServer(in RedisChannel channel, CommandFlags flags, object asyncState, bool internalCall)
             {
                 var oldOwner = Interlocked.Exchange(ref owner, null);
-                if (oldOwner == null) return null;
+                var bridge = oldOwner?.GetBridge(ConnectionType.Subscription, false);
+                if (bridge == null) return null;
+
+                var state = PendingSubscriptionState.Create(channel, this, flags, false, internalCall, asyncState, oldOwner.IsSlave);
 
-                var cmd = channel.IsPatternBased ? RedisCommand.PUNSUBSCRIBE : RedisCommand.UNSUBSCRIBE;
-                var msg = Message.Create(-1, flags, cmd, channel);
-                if (internalCall) msg.SetInternalCall();
-                return oldOwner.WriteDirectAsync(msg, ResultProcessor.TrackSubscriptions, asyncState);
+                if (!bridge.TryEnqueueBackgroundSubscriptionWrite(state))
+                {
+                    state.Abort();
+                    return null;
+                }
+                return state.Task;
+            }
+
+            internal readonly struct PendingSubscriptionState
+            {
+                public override string ToString() => Message.ToString();
+                public Subscription Subscription { get; }
+                public Message Message { get; }
+                public bool IsSlave { get; }
+                public Task Task => _taskSource.Task;
+                private readonly TaskCompletionSource<bool> _taskSource;
+
+                public static PendingSubscriptionState Create(RedisChannel channel, Subscription subscription, CommandFlags flags, bool subscribe, bool internalCall, object asyncState, bool isSlave)
+                    => new PendingSubscriptionState(asyncState, channel, subscription, flags, subscribe, internalCall, isSlave);
+
+                public void Abort() => _taskSource.TrySetCanceled();
+                public void Fail(Exception ex) => _taskSource.TrySetException(ex);
+
+                private PendingSubscriptionState(object asyncState, RedisChannel channel, Subscription subscription, CommandFlags flags, bool subscribe, bool internalCall, bool isSlave)
+                {
+                    
+                    var cmd = subscribe
+                        ? (channel.IsPatternBased ? RedisCommand.PSUBSCRIBE : RedisCommand.SUBSCRIBE)
+                        : (channel.IsPatternBased ? RedisCommand.PUNSUBSCRIBE : RedisCommand.UNSUBSCRIBE);
+                    var msg = Message.Create(-1, flags, cmd, channel);
+                    if (internalCall) msg.SetInternalCall();
+                    var taskSource = TaskSource.Create<bool>(asyncState);
+                    var source = ResultBox<bool>.Get(taskSource);
+                    msg.SetSource(ResultProcessor.TrackSubscriptions, source);
+
+                    Subscription = subscription;
+                    _taskSource = taskSource;
+                    Message = msg;
+                    IsSlave = isSlave;
+                }
             }
 
             internal ServerEndPoint GetOwner() => Volatile.Read(ref owner);
@@ -225,7 +279,9 @@ internal void Resubscribe(in RedisChannel channel, ServerEndPoint server)
                     var cmd = channel.IsPatternBased ? RedisCommand.PSUBSCRIBE : RedisCommand.SUBSCRIBE;
                     var msg = Message.Create(-1, CommandFlags.FireAndForget, cmd, channel);
                     msg.SetInternalCall();
-                    server.WriteDirectFireAndForget(msg, ResultProcessor.TrackSubscriptions);
+#pragma warning disable CS0618
+                    server.WriteDirectFireAndForgetSync(msg, ResultProcessor.TrackSubscriptions);
+#pragma warning restore CS0618
                 }
             }
 

src/StackExchange.Redis/RedisTransaction.cs

@@ -287,7 +287,9 @@ public IEnumerable<Message> GetMessages(PhysicalConnection connection)
                                 sb.AppendLine("checking conditions in the *early* path");
                                 // need to get those sent ASAP; if they are stuck in the buffers, we die
                                 multiplexer.Trace("Flushing and waiting for precondition responses");
-                                connection.FlushSync(true); // make sure they get sent, so we can check for QUEUED (and the pre-conditions if necessary)
+#pragma warning disable CS0618
+                                connection.FlushSync(true, multiplexer.TimeoutMilliseconds); // make sure they get sent, so we can check for QUEUED (and the pre-conditions if necessary)
+#pragma warning restore CS0618
 
                                 if (Monitor.Wait(lastBox, multiplexer.TimeoutMilliseconds))
                                 {
@@ -344,7 +346,9 @@ public IEnumerable<Message> GetMessages(PhysicalConnection connection)
                                 sb.AppendLine("checking conditions in the *late* path");
 
                                 multiplexer.Trace("Flushing and waiting for precondition+queued responses");
-                                connection.FlushSync(true); // make sure they get sent, so we can check for QUEUED (and the pre-conditions if necessary)
+#pragma warning disable CS0618
+                                connection.FlushSync(true, multiplexer.TimeoutMilliseconds); // make sure they get sent, so we can check for QUEUED (and the pre-conditions if necessary)
+#pragma warning restore CS0618
                                 if (Monitor.Wait(lastBox, multiplexer.TimeoutMilliseconds))
                                 {
                                     if (!AreAllConditionsSatisfied(multiplexer))

src/StackExchange.Redis/ResultProcessor.cs

@@ -488,8 +488,7 @@ protected override bool SetResultCore(PhysicalConnection connection, Message mes
                         {
                             hash = ParseSHA1(asciiHash); // external caller wants the hex bytes, not the ascii bytes
                         }
-                        var sl = message as RedisDatabase.ScriptLoadMessage;
-                        if (sl != null)
+                        if (message is RedisDatabase.ScriptLoadMessage sl)
                         {
                             connection.BridgeCouldBeNull?.ServerEndPoint?.AddScript(sl.Script, asciiHash);
                         }
@@ -1413,7 +1412,7 @@ protected override bool SetResultCore(PhysicalConnection connection, Message mes
                     return false;
                 }
 
-                StreamEntry[] entries = null;
+                StreamEntry[] entries;
 
                 if (skipStreamName)
                 {

src/StackExchange.Redis/ServerSelectionStrategy.cs

@@ -61,10 +61,10 @@ public ServerSelectionStrategy(ConnectionMultiplexer multiplexer)
         /// Computes the hash-slot that would be used by the given key
         /// </summary>
         /// <param name="key">The <see cref="RedisKey"/> to determine a slot ID for.</param>
-        public int HashSlot(RedisKey key)
+        public int HashSlot(in RedisKey key)
             => ServerType == ServerType.Standalone ? NoSlot : GetClusterSlot(key);
 
-        private static unsafe int GetClusterSlot(RedisKey key)
+        private static unsafe int GetClusterSlot(in RedisKey key)
         {
             //HASH_SLOT = CRC16(key) mod 16384
             if (key.IsNull) return NoSlot;
@@ -107,7 +107,7 @@ public ServerEndPoint Select(Message message)
             return Select(slot, message.Command, message.Flags);
         }
 
-        public ServerEndPoint Select(RedisCommand command, RedisKey key, CommandFlags flags)
+        public ServerEndPoint Select(RedisCommand command, in RedisKey key, CommandFlags flags)
         {
             int slot = ServerType == ServerType.Cluster ? HashSlot(key) : NoSlot;
             return Select(slot, command, flags);
@@ -155,7 +155,9 @@ public bool TryResend(int hashSlot, Message message, EndPoint endpoint, bool isM
                         else
                         {
                             message.PrepareToResend(resendVia, isMoved);
-                            retry = resendVia.TryWrite(message) == WriteResult.Success;
+#pragma warning disable CS0618
+                            retry = resendVia.TryWriteSync(message) == WriteResult.Success;
+#pragma warning restore CS0618
                         }
                     }
 
@@ -187,7 +189,7 @@ internal int CombineSlot(int oldSlot, int newSlot)
             return oldSlot == newSlot ? oldSlot : MultipleSlots;
         }
 
-        internal int CombineSlot(int oldSlot, RedisKey key)
+        internal int CombineSlot(int oldSlot, in RedisKey key)
         {
             if (oldSlot == MultipleSlots || key.IsNull) return oldSlot;
 

src/StackExchange.Redis/TaskExtensions.cs

@@ -26,6 +26,7 @@ public static Task<T> ObserveErrors<T>(this Task<T> task)
         }
 
         public static ConfiguredTaskAwaitable ForAwait(this Task task) => task.ConfigureAwait(false);
+        public static ConfiguredValueTaskAwaitable ForAwait(this ValueTask task) => task.ConfigureAwait(false);
         public static ConfiguredTaskAwaitable<T> ForAwait<T>(this Task<T> task) => task.ConfigureAwait(false);
         public static ConfiguredValueTaskAwaitable<T> ForAwait<T>(this ValueTask<T> task) => task.ConfigureAwait(false);
 
@@ -37,10 +38,10 @@ public static Task<T> ObserveErrors<T>(this Task<T> task)
         public static async Task<bool> TimeoutAfter(this Task task, int timeoutMs)
         {
             var cts = new CancellationTokenSource();
-            if (task == await Task.WhenAny(task, Task.Delay(timeoutMs, cts.Token)).ConfigureAwait(false))
+            if (task == await Task.WhenAny(task, Task.Delay(timeoutMs, cts.Token)).ForAwait())
             {
                 cts.Cancel();
-                await task.ConfigureAwait(false);
+                await task.ForAwait();
                 return true;
             }
             else

tests/StackExchange.Redis.Tests/PubSubCommand.cs

 using System;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using System.Threading.Tasks;
 using Xunit;
 using Xunit.Abstractions;
 
@@ -31,5 +34,59 @@ public void SubscriberCount()
                 Assert.Contains(channel, channels);
             }
         }
+
+        [Fact]
+        public async Task SubscriberCountAsync()
+        {
+            using (var conn = Create())
+            {
+                RedisChannel channel = Me() + Guid.NewGuid();
+                var server = conn.GetServer(conn.GetEndPoints()[0]);
+
+                var channels = await server.SubscriptionChannelsAsync(Me() + "*").WithTimeout(2000);
+                Assert.DoesNotContain(channel, channels);
+
+                long justWork = await server.SubscriptionPatternCountAsync().WithTimeout(2000);
+                var count = await server.SubscriptionSubscriberCountAsync(channel).WithTimeout(2000);
+                Assert.Equal(0, count);
+                await conn.GetSubscriber().SubscribeAsync(channel, delegate { }).WithTimeout(2000);
+                count = await server.SubscriptionSubscriberCountAsync(channel).WithTimeout(2000);
+                Assert.Equal(1, count);
+
+                channels = await server.SubscriptionChannelsAsync(Me() + "*").WithTimeout(2000);
+                Assert.Contains(channel, channels);
+            }
+        }
+    }
+    static class Util
+    {
+        public static async Task WithTimeout(this Task task, int timeoutMs,
+            [CallerMemberName] string caller = null, [CallerLineNumber] int line = 0)
+        {
+            var cts = new CancellationTokenSource();
+            if (task == await Task.WhenAny(task, Task.Delay(timeoutMs, cts.Token)).ForAwait())
+            {
+                cts.Cancel();
+                await task.ForAwait();
+            }
+            else
+            {
+                throw new TimeoutException($"timout from {caller} line {line}");
+            }
+        }
+        public static async Task<T> WithTimeout<T>(this Task<T> task, int timeoutMs,
+            [CallerMemberName] string caller = null, [CallerLineNumber] int line = 0)
+        {
+            var cts = new CancellationTokenSource();
+            if (task == await Task.WhenAny(task, Task.Delay(timeoutMs, cts.Token)).ForAwait())
+            {
+                cts.Cancel();
+                return await task.ForAwait();
+            }
+            else
+            {
+                throw new TimeoutException($"timout from {caller} line {line}");
+            }
+        }
     }
 }

toys/TestConsole/Program.cs

@@ -8,55 +8,16 @@ namespace TestConsole
 {
     internal static class Program
     {
-        private const int taskCount = 10;
-        private const int totalRecords = 100000;
-
-        private static void Main()
-        {
-#if SEV2
-        Pipelines.Sockets.Unofficial.SocketConnection.AssertDependencies();
-        Console.WriteLine("We loaded the things...");
-        // Console.ReadLine();
-#endif
-
-            Stopwatch stopwatch = new Stopwatch();
-            stopwatch.Start();
-
-            var taskList = new List<Task>();
-            var connection = ConnectionMultiplexer.Connect("127.0.0.1");
-            for (int i = 0; i < taskCount; i++)
-            {
-                var i1 = i;
-                var task = new Task(() => Run(i1, connection));
-                task.Start();
-                taskList.Add(task);
-            }
-
-            Task.WaitAll(taskList.ToArray());
-
-            stopwatch.Stop();
-
-            Console.WriteLine($"Done. {stopwatch.ElapsedMilliseconds}");
-            Console.ReadLine();
-        }
-
-        private static void Run(int taskId, ConnectionMultiplexer connection)
+        public static async Task Main()
         {
-            Console.WriteLine($"{taskId} Started");
-            var database = connection.GetDatabase(0);
-
-            for (int i = 0; i < totalRecords; i++)
-            {
-                database.StringSet(i.ToString(), i.ToString());
-            }
-
-            Console.WriteLine($"{taskId} Insert completed");
-
-            for (int i = 0; i < totalRecords; i++)
+            using (var muxer = await ConnectionMultiplexer.ConnectAsync("127.0.0.1"))
             {
-                var result = database.StringGet(i.ToString());
+                var db = muxer.GetDatabase();
+                var sub = muxer.GetSubscriber();
+                Console.WriteLine("subscribing");
+                ChannelMessageQueue queue = await sub.SubscribeAsync("yolo");
+                Console.WriteLine("subscribed");
             }
-            Console.WriteLine($"{taskId} Completed");
         }
     }
 }