Less async birthday updates; download users on connect

From testing, it appears DownloadUsersAsync hangs forever and has other
consequences if its corresponding server is not fully connected, or is
struggling to connect. This is despite all attempts to mitigate it and
detect any disconnections shortly before attempting it.
Additionally, birthday updates are now run asynchronously per shard, but
synchronously per guild in an attempt to keep rare instances of rate
limiting under control.

BackgroundServices/BirthdayRoleUpdate.cs

@@ -23,9 +23,11 @@ namespace BirthdayBot.BackgroundServices
         public override async Task OnTick()
         {
             var tasks = new List<Task>();
-            foreach (var guild in BotInstance.DiscordClient.Guilds)
+
+            // Work on each shard concurrently; guilds within each shard synchronously
+            foreach (var shard in BotInstance.DiscordClient.Shards)
             {
-                tasks.Add(ProcessGuildAsync(guild));
+                tasks.Add(ProcessShardAsync(shard));
             }
             var alltasks = Task.WhenAll(tasks);
 
@@ -60,6 +62,39 @@ namespace BirthdayBot.BackgroundServices
         /// <returns>Diagnostic data in string form.</returns>
         public async Task<string> SingleProcessGuildAsync(SocketGuild guild) => (await ProcessGuildAsync(guild)).Export();
 
+        /// <summary>
+        /// Called by <see cref="OnTick"/>, processes all guilds within a shard synchronously.
+        /// </summary>
+        private async Task ProcessShardAsync(DiscordSocketClient shard)
+        {
+            if (shard.ConnectionState != Discord.ConnectionState.Connected)
+            {
+                Log($"Shard {shard.ShardId} (with {shard.Guilds.Count} guilds) processing stopped - shard disconnected.");
+                return;
+            }
+            var exs = new List<Exception>();
+            foreach (var guild in shard.Guilds)
+            {
+                try
+                {
+                    // Check if shard remains available
+                    if (shard.ConnectionState != Discord.ConnectionState.Connected)
+                    {
+                        Log($"Shard {shard.ShardId} (with {shard.Guilds.Count} guilds) processing interrupted.");
+                        return;
+                    }
+                    await ProcessGuildAsync(guild);
+                }
+                catch (Exception ex)
+                {
+                    // Catch all exceptions per-guild but continue processing, throw at end
+                    exs.Add(ex);
+                }
+            }
+            Log($"Shard {shard.ShardId} (with {shard.Guilds.Count} guilds) processing completed.");
+            if (exs.Count != 0) throw new AggregateException(exs);
+        }
+
         /// <summary>
         /// Main method where actual guild processing occurs.
         /// </summary>
@@ -78,7 +113,7 @@ namespace BirthdayBot.BackgroundServices
             if (diag.RoleCheck != null) return diag;
 
             // Determine who's currently having a birthday
-            await guild.DownloadUsersAsync();
+            //await guild.DownloadUsersAsync();
             var users = await GuildUserConfiguration.LoadAllAsync(guild.Id);
             var tz = gc.TimeZone;
             var birthdays = GetGuildCurrentBirthdays(users, tz);

Program.cs

@@ -21,6 +21,7 @@ namespace BirthdayBot
 
             var dc = new DiscordSocketConfig()
             {
+                AlwaysDownloadUsers = true,
                 DefaultRetryMode = RetryMode.RetryRatelimit,
                 MessageCacheSize = 0,
                 TotalShards = cfg.ShardCount,