From f958ba5ddd9a2ddf7c805ffe47525e4e1e93f884 Mon Sep 17 00:00:00 2001
From: henry <henry@hobbs.zone>
Date: Fri, 4 Jul 2025 12:07:22 -0400
Subject: [PATCH] Modify repo to use concurrent dictionaries for thread safety
 during backup

---
 .../Data/TakeANumberAccessQueueRepo.cs        | 51 ++++++++++---------
 1 file changed, 26 insertions(+), 25 deletions(-)

diff --git a/AccessQueueService/Data/TakeANumberAccessQueueRepo.cs b/AccessQueueService/Data/TakeANumberAccessQueueRepo.cs
index ad45a83..1cf3b1b 100644
--- a/AccessQueueService/Data/TakeANumberAccessQueueRepo.cs
+++ b/AccessQueueService/Data/TakeANumberAccessQueueRepo.cs
@@ -1,4 +1,5 @@
-using System.Runtime.Serialization;
+using System.Collections.Concurrent;
+using System.Runtime.Serialization;
 using System.Text.Json;
 using AccessQueueService.Models;
 using Microsoft.Extensions.Configuration;
@@ -7,9 +8,9 @@ namespace AccessQueueService.Data
 {
     public class TakeANumberAccessQueueRepo : IAccessQueueRepo
     {
-        private Dictionary<string, AccessTicket> _accessTickets = [];
-        private Dictionary<string, ulong> _queueNumbers = [];
-        private Dictionary<ulong, AccessTicket> _accessQueue = [];
+        private ConcurrentDictionary<string, AccessTicket> _accessTickets = new();
+        private ConcurrentDictionary<string, ulong> _queueNumbers = new();
+        private ConcurrentDictionary<ulong, AccessTicket> _accessQueue = new();
 
         internal ulong _nowServing = 0;
         internal ulong _nextUnusedTicket = 0;
@@ -47,12 +48,12 @@ namespace AccessQueueService.Data
         public int DeleteExpiredTickets()
         {
             var cutoff = DateTime.UtcNow;
-            var expiredTickets = _accessTickets.Where(t => t.Value.ExpiresOn < cutoff);
+            var expiredTickets = _accessTickets.Where(t => t.Value.ExpiresOn < cutoff).ToList();
             int count = 0;
             foreach (var ticket in expiredTickets)
             {
                 count++;
-                _accessTickets.Remove(ticket.Key);
+                _accessTickets.TryRemove(ticket.Key, out _);
             }
             return count;
         }
@@ -70,13 +71,13 @@ namespace AccessQueueService.Data
             int filledSpots = 0;
             while (filledSpots < openSpots && _nowServing < _nextUnusedTicket)
             {
-                if (_accessQueue.TryGetValue(_nowServing, out var nextUser))
+                if (_accessQueue.TryRemove(_nowServing, out var nextUser))
                 {
-                    _accessQueue.Remove(_nowServing);
-                    _queueNumbers.Remove(nextUser.UserId);
+                    _queueNumbers.TryRemove(nextUser.UserId, out _);
                     if (nextUser.LastActive < activeCutoff)
                     {
                         // User is inactive, throw away their ticket
+                        _nowServing++;
                         continue;
                     }
                     _accessTickets[nextUser.UserId] = new AccessTicket
@@ -104,24 +105,25 @@ namespace AccessQueueService.Data
 
         public bool RemoveUser(string userId)
         {
-            if (_queueNumbers.TryGetValue(userId, out var queueNumber))
+            if (_queueNumbers.TryRemove(userId, out var queueNumber))
             {
-                _accessQueue.Remove(queueNumber);
-                _queueNumbers.Remove(userId);
+                _accessQueue.TryRemove(queueNumber, out _);
             }
-            return _accessTickets.Remove(userId);
+            return _accessTickets.TryRemove(userId, out _);
         }
 
         internal void Optimize()
         {
-            var newQueue = new Dictionary<ulong, AccessTicket>();
-            var newQueueNumbers = new Dictionary<string, ulong>();
+            var newQueue = new ConcurrentDictionary<ulong, AccessTicket>();
+            var newQueueNumbers = new ConcurrentDictionary<string, ulong>();
             ulong newIndex = 0;
             for (ulong i = _nowServing; i < _nextUnusedTicket; i++)
             {
-                var user = _accessQueue[i];
-                newQueue[newIndex] = user;
-                newQueueNumbers[user.UserId] = newIndex++;
+                if (_accessQueue.TryGetValue(i, out var user))
+                {
+                    newQueue[newIndex] = user;
+                    newQueueNumbers[user.UserId] = newIndex++;
+                }
             }
             _accessQueue = newQueue;
             _queueNumbers = newQueueNumbers;
@@ -133,10 +135,9 @@ namespace AccessQueueService.Data
         {
             var state = new TakeANumberAccessQueueRepoState
             {
-                AccessTickets = _accessTickets,
-                AccessQueue = _accessQueue,
+                AccessTickets = new Dictionary<string, AccessTicket>(_accessTickets),
+                AccessQueue = new Dictionary<ulong, AccessTicket>(_accessQueue),
             };
-
             return JsonSerializer.Serialize(state);
         }
 
@@ -148,14 +149,14 @@ namespace AccessQueueService.Data
                 return new();
             }
 
-            var _accessTickets = state.AccessTickets;
-            var _accessQueue = state.AccessQueue;
+            var _accessTickets = new ConcurrentDictionary<string, AccessTicket>(state.AccessTickets);
+            var _accessQueue = new ConcurrentDictionary<ulong, AccessTicket>(state.AccessQueue);
             var _nextUnusedTicket = 0ul;
             var _nowServing = ulong.MaxValue;
-            Dictionary<string, ulong> _queueNumbers = [];
+            var _queueNumbers = new ConcurrentDictionary<string, ulong>();
             foreach (var queueItem in state.AccessQueue)
             {
-                _queueNumbers.Add(queueItem.Value.UserId, queueItem.Key);
+                _queueNumbers[queueItem.Value.UserId] = queueItem.Key;
                 _nextUnusedTicket = Math.Max(_nextUnusedTicket, queueItem.Key + 1);
                 _nowServing = Math.Min(_nowServing, queueItem.Key);
             }