Merge pull request '#14 Cache active user count for performance' (#32) from cache-active-user-count into main

Reviewed-on: #32

AccessQueuePlayground/Components/Pages/Config.razor

@@ -31,6 +31,14 @@
 			<div class="text-danger">Please enter a positive integer.</div>
 		}
 	</div>
+	<div class="mb-3">
+		<label for="cacheMillis">Cache Milliseconds</label>
+		<TextInput Id="cacheMillis" @bind-Value="config.CacheMilliseconds" Type="TextInputType.Number" />
+		@if (!isCacheMillisValid)
+		{
+			<div class="text-danger">Please enter a positive integer or zero.</div>
+		}
+	</div>
 	<div class="mb-3">
 		<Switch Id="rollingExpiration" @bind-Value="config.RollingExpiration" Label="Rolling Expiration" />
 	</div>
@@ -46,6 +54,7 @@
 	private bool isCapacityLimitValid = true;
 	private bool isActivitySecondsValid = true;
 	private bool isExpirationSecondsValid = true;
+	private bool isCacheMillisValid = true;
 	private string? successMessage;
 
 	protected override void OnInitialized()
@@ -56,18 +65,20 @@
 				ActivitySeconds = (current.ActivitySeconds ?? 0).ToString(),
 				CapacityLimit = (current.CapacityLimit ?? 0).ToString(),
 				ExpirationSeconds = (current.ExpirationSeconds ?? 0).ToString(),
+				CacheMilliseconds = (current.CacheMilliseconds ?? 0).ToString(),
 				RollingExpiration = current.RollingExpiration ?? false
 			};
 		ValidateInputs();
 	}
 
-	private bool IsFormValid => isCapacityLimitValid && isActivitySecondsValid && isExpirationSecondsValid;
+	private bool IsFormValid => isCapacityLimitValid && isActivitySecondsValid && isExpirationSecondsValid && isCacheMillisValid;
 
 	private void ValidateInputs()
 	{
 		isCapacityLimitValid = int.TryParse(config.CapacityLimit, out var cap) && cap > 0;
 		isActivitySecondsValid = int.TryParse(config.ActivitySeconds, out var act) && act > 0;
 		isExpirationSecondsValid = int.TryParse(config.ExpirationSeconds, out var exp) && exp > 0;
+		isCacheMillisValid = int.TryParse(config.CacheMilliseconds, out var cache) && cache >= 0;
 	}
 
 	private async Task HandleValidSubmit()
@@ -81,6 +92,7 @@
 			ActivitySeconds = int.Parse(config.ActivitySeconds),
 			CapacityLimit = int.Parse(config.CapacityLimit),
 			ExpirationSeconds = int.Parse(config.ExpirationSeconds),
+			CacheMilliseconds = int.Parse(config.CacheMilliseconds),
 			RollingExpiration = config.RollingExpiration
 		}));
 		successMessage = "Configuration updated successfully.";
@@ -91,6 +103,7 @@
 		public string CapacityLimit { get; set; } = "";
 		public string ActivitySeconds { get; set; } = "";
 		public string ExpirationSeconds { get; set; } = "";
+		public string CacheMilliseconds { get; set; } = "";
 		public bool RollingExpiration { get; set; }
 	}
 }

AccessQueueService/Data/IAccessQueueRepo.cs

@@ -16,6 +16,6 @@ namespace AccessQueueService.Data
         public void Enqueue(AccessTicket ticket);
         public int DeleteExpiredTickets();
         public bool RemoveUser(string userId);
-        public bool DidDequeueUntilFull(int activeSeconds, int expirationSeconds, int capacityLimit);
+        public bool DidDequeueUntilFull(AccessQueueConfig config);
     }
 }

AccessQueueService/Data/TakeANumberAccessQueueRepo.cs

@@ -15,6 +15,9 @@ namespace AccessQueueService.Data
         internal ulong _nowServing = 0;
         internal ulong _nextUnusedTicket = 0;
 
+        private int? _cachedActiveUsers = null;
+        private DateTime _cachedActiveUsersTime = DateTime.MinValue;
+
         public int GetUnexpiredTicketsCount() => _accessTickets.Count(t => t.Value.ExpiresOn > DateTime.UtcNow);
         public int GetActiveTicketsCount(DateTime activeCutoff) => _accessTickets
             .Count(t => t.Value.ExpiresOn > DateTime.UtcNow && t.Value.LastActive > activeCutoff);
@@ -58,37 +61,80 @@ namespace AccessQueueService.Data
             return count;
         }
 
-        public bool DidDequeueUntilFull(int activeSeconds, int expirationSeconds, int capacityLimit)
+        private bool HasValidActiveUsersCache(AccessQueueConfig config, DateTime now)
         {
-            var now = DateTime.UtcNow;
+            return config.CacheMilliseconds.HasValue && _cachedActiveUsers.HasValue && (now - _cachedActiveUsersTime).TotalMilliseconds < config.CacheMilliseconds.Value;
-            var activeCutoff = now.AddSeconds(-activeSeconds);
-            var numberOfActiveUsers = _accessTickets.Count(t => t.Value.ExpiresOn > now && t.Value.LastActive > activeCutoff);
-            var openSpots = capacityLimit - numberOfActiveUsers;
-            if (openSpots <= 0)
-            {
-                return true;
         }
+
+        private int GetOpenSpots(AccessQueueConfig config, int activeUsers)
+        {
+            return config.CapacityLimit.Value - activeUsers;
+        }
+
+        private int UpdateActiveUsersCache(DateTime now, DateTime activeCutoff)
+        {
+            _cachedActiveUsers = _accessTickets.Count(t => t.Value.ExpiresOn > now && t.Value.LastActive > activeCutoff);
+            _cachedActiveUsersTime = now;
+            return _cachedActiveUsers.GetValueOrDefault();
+        }
+
+        private int DequeueUsersUntilFull(int openSpots, DateTime now, DateTime activeCutoff, AccessQueueConfig config)
+        {
             int filledSpots = 0;
             while (filledSpots < openSpots && _nowServing < _nextUnusedTicket)
             {
-                if (_accessQueue.TryRemove(_nowServing, out var nextUser))
+                if (_accessQueue.TryRemove(_nowServing++, out var nextUser))
                 {
                     _queueNumbers.TryRemove(nextUser.UserId, out _);
                     if (nextUser.LastActive < activeCutoff)
                     {
                         // User is inactive, throw away their ticket
-                        _nowServing++;
                         continue;
                     }
                     _accessTickets[nextUser.UserId] = new AccessTicket
                     {
                         UserId = nextUser.UserId,
-                        ExpiresOn = now.AddSeconds(expirationSeconds),
+                        ExpiresOn = now.AddSeconds(config.ExpirationSeconds ?? 0),
                         LastActive = now
                     };
                     filledSpots++;
                 }
-                _nowServing++;
+            }
+            return filledSpots;
+        }
+
+        public bool DidDequeueUntilFull(AccessQueueConfig config)
+        {
+            var now = DateTime.UtcNow;
+            if (!config.ActivitySeconds.HasValue || !config.ExpirationSeconds.HasValue || !config.CapacityLimit.HasValue)
+            {
+                throw new Exception("Required config values are not defined.");
+            }
+            var activeCutoff = now.AddSeconds(-config.ActivitySeconds.Value);
+
+            int activeUsers;
+            if (HasValidActiveUsersCache(config, now))
+            {
+                activeUsers = _cachedActiveUsers.GetValueOrDefault();
+            }
+            else
+            {
+                activeUsers = UpdateActiveUsersCache(now, activeCutoff);
+            }
+
+            var openSpots = GetOpenSpots(config, activeUsers);
+            if (openSpots <= 0)
+            {
+                return true;
+            }
+
+            int filledSpots = DequeueUsersUntilFull(openSpots, now, activeCutoff, config);
+
+            // Invalidate cache if any users were granted access
+            if (filledSpots > 0)
+            {
+                _cachedActiveUsers = null;
+                _cachedActiveUsersTime = DateTime.MinValue;
             }
             return filledSpots == openSpots;
         }
@@ -101,6 +147,8 @@ namespace AccessQueueService.Data
         public void UpsertTicket(AccessTicket ticket)
         {
             _accessTickets[ticket.UserId] = ticket;
+            _cachedActiveUsers = null;
+            _cachedActiveUsersTime = DateTime.MinValue;
         }
 
         public bool RemoveUser(string userId)

AccessQueueService/Models/AccessQueueConfig.cs

@@ -6,6 +6,7 @@ namespace AccessQueueService.Models
         public int? ActivitySeconds { get; set; }
         public int? ExpirationSeconds { get; set; }
         public bool? RollingExpiration { get; set; }
+        public int? CacheMilliseconds { get; set; }
 
         public AccessQueueConfig Clone()
         {

AccessQueueService/Services/AccessService.cs

@@ -23,7 +23,8 @@ namespace AccessQueueService.Services
                 ExpirationSeconds = _configuration.GetValue<int>("AccessQueue:ExpirationSeconds"),
                 ActivitySeconds = _configuration.GetValue<int>("AccessQueue:ActivitySeconds"),
                 CapacityLimit = _configuration.GetValue<int>("AccessQueue:CapacityLimit"),
-                RollingExpiration = _configuration.GetValue<bool>("AccessQueue:RollingExpiration")
+                RollingExpiration = _configuration.GetValue<bool>("AccessQueue:RollingExpiration"),
+                CacheMilliseconds = _configuration.GetValue<int>("AccessQueue:CacheMilliseconds")
             };
         }
         public AccessQueueConfig GetConfiguration() => _config.Clone();
@@ -53,10 +54,7 @@ namespace AccessQueueService.Services
             await _queueLock.WaitAsync();
             try
             {
-                var hasCapacity = !_accessQueueRepo.DidDequeueUntilFull(
+                var hasCapacity = !_accessQueueRepo.DidDequeueUntilFull(_config);
-                    _config.ActivitySeconds.Value,
-                    _config.ExpirationSeconds.Value,
-                    _config.CapacityLimit.Value);
                 var existingTicket = _accessQueueRepo.GetTicket(userId);
                 if (existingTicket != null && existingTicket.ExpiresOn > DateTime.UtcNow)
                 {
@@ -109,6 +107,10 @@ namespace AccessQueueService.Services
                         });
                         _logger.LogInformation("User {UserId} added to queue. Requests ahead: {RequestsAhead}.", userId, requestsAhead);
                     }
+                    else
+                    {
+                        _logger.LogInformation("User {UserId} already in queue. Requests ahead: {RequestsAhead}.", userId, requestsAhead);
+                    }
                     return new AccessResponse
                     {
                         ExpiresOn = null,

AccessQueueService/appsettings.json

@@ -30,7 +30,8 @@
     "RollingExpiration": true,
     "CleanupIntervalSeconds": 60,
     "BackupFilePath": "Logs\\backup.json",
-        "BackupIntervalSeconds": 5
+    "BackupIntervalSeconds": 5,
+    "CacheMilliseconds": 1000
   },
   "AllowedHosts": "*"
 }

AccessQueueServiceTests/AccessQueueRepoTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net.Sockets;
 using System.Text;
 using System.Text.Json;
 using System.Threading.Tasks;
@@ -14,12 +15,43 @@ namespace AccessQueueServiceTests
     public class AccessQueueRepoTests
     {
         private readonly TakeANumberAccessQueueRepo _repo;
+        private readonly AccessQueueConfig _simpleConfig = new()
+        {
+            ExpirationSeconds = 60,
+            ActivitySeconds = 60,
+            CapacityLimit = 1,
+            RollingExpiration = false,
+            CacheMilliseconds = null
+        };
+        private readonly AccessQueueConfig _configWithCache = new()
+        {
+            ExpirationSeconds = 60,
+            ActivitySeconds = 60,
+            CapacityLimit = 1,
+            RollingExpiration = false,
+            CacheMilliseconds = 100
+        };
+        private AccessQueueConfig SimpleConfigWithCapacity(int capacity) => new()
+        {
+            ExpirationSeconds = 60,
+            ActivitySeconds = 60,
+            CapacityLimit = capacity,
+            RollingExpiration = false,
+            CacheMilliseconds = null
+        };
 
         public AccessQueueRepoTests()
         {
             _repo = new TakeANumberAccessQueueRepo();
         }
 
+        private List<AccessTicket> GetSimpleTicketList() => new()
+        {
+            new() { UserId = "first", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow },
+            new() { UserId = "second", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow },
+            new() { UserId = "third", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow }
+        };
+
         [Fact]
         public void GetUnexpiredTicketsCount_ReturnsCorrectCount()
         {
@@ -91,7 +123,7 @@ namespace AccessQueueServiceTests
 
             var ticket = new AccessTicket { UserId = "a", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
             _repo.Enqueue(ticket);
-            bool result = _repo.DidDequeueUntilFull(60, 60, 1);
+            bool result = _repo.DidDequeueUntilFull(_simpleConfig);
             Assert.True(result);
             Assert.NotNull(_repo.GetTicket("a"));
         }
@@ -101,7 +133,7 @@ namespace AccessQueueServiceTests
         {
 
             _repo.UpsertTicket(new AccessTicket { UserId = "a", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow });
-            bool result = _repo.DidDequeueUntilFull(60, 60, 0);
+            bool result = _repo.DidDequeueUntilFull(SimpleConfigWithCapacity(0));
             Assert.True(result);
         }
 
@@ -155,7 +187,7 @@ namespace AccessQueueServiceTests
             var active = new AccessTicket { UserId = "active", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
             _repo.Enqueue(inactive);
             _repo.Enqueue(active);
-            bool result = _repo.DidDequeueUntilFull(5 * 60, 60, 1);
+            bool result = _repo.DidDequeueUntilFull(_simpleConfig);
             Assert.True(result);
             Assert.Null(_repo.GetTicket("inactive"));
             Assert.NotNull(_repo.GetTicket("active"));
@@ -164,12 +196,10 @@ namespace AccessQueueServiceTests
         [Fact]
         public void Enqueue_QueuesUsersInOrder()
         {
-            var ticket1 = new AccessTicket { UserId = "first", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow };
+            foreach (var ticket in GetSimpleTicketList())
-            var ticket2 = new AccessTicket { UserId = "second", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow };
+            {
-            var ticket3 = new AccessTicket { UserId = "third", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow };
+                _repo.Enqueue(ticket);
-            _repo.Enqueue(ticket1);
+            }
-            _repo.Enqueue(ticket2);
-            _repo.Enqueue(ticket3);
             Assert.Equal(0, _repo.GetRequestsAhead("first"));
             Assert.Equal(1, _repo.GetRequestsAhead("second"));
             Assert.Equal(2, _repo.GetRequestsAhead("third"));
@@ -178,14 +208,12 @@ namespace AccessQueueServiceTests
         [Fact]
         public void DidDequeueUntilFull_DequeuesUsersInOrder()
         {
-            var ticket1 = new AccessTicket { UserId = "first", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+            foreach (var ticket in GetSimpleTicketList())
-            var ticket2 = new AccessTicket { UserId = "second", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+            {
-            var ticket3 = new AccessTicket { UserId = "third", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+                _repo.Enqueue(ticket);
-            _repo.Enqueue(ticket1);
+            }
-            _repo.Enqueue(ticket2);
-            _repo.Enqueue(ticket3);
 
-            bool result = _repo.DidDequeueUntilFull(60 * 60, 60, 1);
+            bool result = _repo.DidDequeueUntilFull(_simpleConfig);
 
             Assert.True(result);
             Assert.NotNull(_repo.GetTicket("first"));
@@ -193,17 +221,33 @@ namespace AccessQueueServiceTests
             Assert.Null(_repo.GetTicket("third"));
         }
 
+        [Fact]
+        public void DidDequeuedUntilFull_CachesActiveTickets_WhenCacheMillisSet()
+        {
+            foreach (var ticket in GetSimpleTicketList())
+            {
+                _repo.Enqueue(ticket);
+            }
+
+            Assert.True(_repo.DidDequeueUntilFull(_configWithCache));
+            Assert.NotNull(_repo.GetTicket("first"));
+            Assert.Null(_repo.GetTicket("second"));
+            Assert.Null(_repo.GetTicket("third"));
+
+            Assert.True(_repo.DidDequeueUntilFull(_configWithCache));
+            Assert.Null(_repo.GetTicket("second"));
+            Assert.Null(_repo.GetTicket("third"));
+        }
+
         [Fact]
         public void Optimize_MaintainsQueueOrder()
         {
-            var ticket1 = new AccessTicket { UserId = "first", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+            foreach (var ticket in GetSimpleTicketList())
-            var ticket2 = new AccessTicket { UserId = "second", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+            {
-            var ticket3 = new AccessTicket { UserId = "third", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+                _repo.Enqueue(ticket);
-            _repo.Enqueue(ticket1);
+            }
-            _repo.Enqueue(ticket2);
-            _repo.Enqueue(ticket3);
 
-            _repo.DidDequeueUntilFull(60 * 60, 60, 1);
+            _repo.DidDequeueUntilFull(_simpleConfig);
             _repo.Optimize();
 
             Assert.NotNull(_repo.GetTicket("first"));
@@ -211,7 +255,7 @@ namespace AccessQueueServiceTests
             Assert.Equal(1, _repo.GetRequestsAhead("third"));
             Assert.Equal(0ul, _repo._nowServing);
 
-            _repo.DidDequeueUntilFull(60 * 60, 60, 2);
+            _repo.DidDequeueUntilFull(SimpleConfigWithCapacity(2));
             Assert.NotNull(_repo.GetTicket("second"));
             Assert.Equal(0, _repo.GetRequestsAhead("third"));
         }
@@ -219,16 +263,13 @@ namespace AccessQueueServiceTests
         [Fact]
         public void Enqueue_MaintainsQueueOrder_WhenMaxValueExceeded()
         {
-            var ticket1 = new AccessTicket { UserId = "first", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
-            var ticket2 = new AccessTicket { UserId = "second", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
-            var ticket3 = new AccessTicket { UserId = "third", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
-
             _repo._nowServing = long.MaxValue - 1;
             _repo._nextUnusedTicket = long.MaxValue - 1;
 
-            _repo.Enqueue(ticket1);
+            foreach (var ticket in GetSimpleTicketList())
-            _repo.Enqueue(ticket2);
+            {
-            _repo.Enqueue(ticket3);
+                _repo.Enqueue(ticket);
+            }
 
             Assert.Equal(0ul, _repo._nowServing);
             Assert.Equal(3ul, _repo._nextUnusedTicket);

AccessQueueServiceTests/AccessServiceTests.cs

@@ -16,6 +16,7 @@ namespace AccessQueueServiceTests
         const int ACT_MILLIS = 1000 * ACT_SECONDS;
         const int CAP_LIMIT = 5;
         const int BULK_COUNT = 10000;
+        const int CACHE_MILLIS = 1000;
         private readonly AccessService _accessService;
 
         public AccessServiceTests()
@@ -25,7 +26,8 @@ namespace AccessQueueServiceTests
                     { "AccessQueue:ExpirationSeconds", $"{EXP_SECONDS}" },
                     { "AccessQueue:ActivitySeconds", $"{ACT_SECONDS}" },
                     { "AccessQueue:CapacityLimit", $"{CAP_LIMIT}" },
-                    { "AccessQueue:RollingExpiration", "true" }
+                    { "AccessQueue:RollingExpiration", "true" },
+                    { "AccessQueue:CacheMilliseconds", $"{CACHE_MILLIS}" }
                 };
 
             var configuration = new ConfigurationBuilder()
@@ -87,9 +89,9 @@ namespace AccessQueueServiceTests
             Assert.NotNull(response);
             Assert.Null(response.ExpiresOn);
             Assert.True(response.RequestsAhead == CAP_LIMIT);
-            Assert.Equal(5, _accessService.UnexpiredTicketsCount);
+            Assert.Equal(CAP_LIMIT, _accessService.UnexpiredTicketsCount);
-            Assert.Equal(5, _accessService.ActiveTicketsCount);
+            Assert.Equal(CAP_LIMIT, _accessService.ActiveTicketsCount);
-            Assert.Equal(6, _accessService.QueueCount);
+            Assert.Equal(CAP_LIMIT + 1, _accessService.QueueCount);
         }
 
 

README.md

@@ -78,13 +78,19 @@ It is possible for the number of users with access to temporarily exceed the `Ca
 
 Configuration is set in `appsettings.json` or via environment variables. The main configuration section is `AccessQueue`:
 
-- **CapacityLimit**: The maximum number of users that can have access at the same time (default: 100).
+**Required variables:**
-- **ActivitySeconds**: How long (in seconds) a user can remain active before being considered inactive (default: 900).
+
-- **ExpirationSeconds**: How long (in seconds) before an access ticket expires (default: 43200).
+- **CapacityLimit**: The maximum number of users that can have access at the same time.
-- **RollingExpiration**: If true, the expiration timer resets on activity (default: true).
+- **ActivitySeconds**: How long (in seconds) a user can remain active before being considered inactive.
-- **CleanupIntervalSeconds**: How often (in seconds) the background cleanup runs to remove expired/inactive users (default: 60).
+- **ExpirationSeconds**: How long (in seconds) before an access ticket expires.
-- **BackupFilePath**: The file path where the access queue state will be periodically saved (no default; optional).
+- **RollingExpiration**: If true, the expiration timer resets on activity.
-- **BackupIntervalSeconds**: How often (in seconds) the state is backed up to disk (no default; optional).
+- **CleanupIntervalSeconds**: How often (in seconds) the background cleanup runs to remove expired/inactive users.
+
+**Optional variables:**
+
+- **BackupFilePath**: The file path where the access queue state will be periodically saved.
+- **BackupIntervalSeconds**: How often (in seconds) the state is backed up to disk.
+- **CacheMilliseconds**: How long (in milliseconds) to cache the active user count before recalculating. Lower values mean more frequent recalculation (more accurate, higher CPU usage). Higher values improve performance but may cause a slight delay in recognizing open spots.
 
 Example `appsettings.json`:
 ```json
@@ -94,7 +100,8 @@ Example `appsettings.json`:
     "ActivitySeconds": 900,
     "ExpirationSeconds": 43200,
     "RollingExpiration": true,
-    "CleanupIntervalSeconds": 60
+    "CleanupIntervalSeconds": 60,
+    "CacheMilliseconds": 1000
   }
 }
 ```