Make collections thread-safe for AI and character systems

Refactored various collections (lists, dictionaries, queues, and caches) in AI, character, animation, and item component systems to use thread-safe patterns and concurrent data structures. This includes introducing copy-on-write wrappers, ConcurrentDictionary, ConcurrentQueue, and ThreadLocal where appropriate to ensure safe concurrent access and mutation, improving stability in multi-threaded scenarios.

Barotrauma/BarotraumaShared/SharedSource/Characters/AI/AITarget.cs

@@ -1,13 +1,67 @@
 using Microsoft.Xna.Framework;
 using System;
 using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
 using System.Xml.Linq;
 
 namespace Barotrauma
 {
+    /// <summary>
+    /// Thread-safe wrapper for AITarget list operations.
+    /// Uses copy-on-write pattern for lock-free reads.
+    /// </summary>
+    class ThreadSafeAITargetList : IEnumerable<AITarget>
+    {
+        private volatile List<AITarget> _list = new List<AITarget>();
+        private readonly object _writeLock = new object();
+
+        public int Count => _list.Count;
+
+        public void Add(AITarget target)
+        {
+            lock (_writeLock)
+            {
+                var newList = new List<AITarget>(_list) { target };
+                Interlocked.Exchange(ref _list, newList);
+            }
+        }
+
+        public bool Remove(AITarget target)
+        {
+            lock (_writeLock)
+            {
+                var newList = new List<AITarget>(_list);
+                bool removed = newList.Remove(target);
+                if (removed)
+                {
+                    Interlocked.Exchange(ref _list, newList);
+                }
+                return removed;
+            }
+        }
+
+        public void Clear()
+        {
+            Interlocked.Exchange(ref _list, new List<AITarget>());
+        }
+
+        public bool Contains(AITarget target) => _list.Contains(target);
+
+        public AITarget this[int index] => _list[index];
+
+        public IEnumerator<AITarget> GetEnumerator() => _list.GetEnumerator();
+        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => GetEnumerator();
+
+        public List<AITarget> ToList() => new List<AITarget>(_list);
+        public AITarget FirstOrDefault(Func<AITarget, bool> predicate) => _list.FirstOrDefault(predicate);
+        public IEnumerable<AITarget> Where(Func<AITarget, bool> predicate) => _list.Where(predicate);
+        public bool Any(Func<AITarget, bool> predicate) => _list.Any(predicate);
+    }
+
     partial class AITarget
     {
-        public static List<AITarget> List = new List<AITarget>();
+        public static ThreadSafeAITargetList List = new ThreadSafeAITargetList();
 
         private Entity entity;
         public Entity Entity

Barotrauma/BarotraumaShared/SharedSource/Characters/AI/HumanAIController.cs

@@ -5,6 +5,7 @@ using Microsoft.Xna.Framework;
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 
 namespace Barotrauma
 {
@@ -1817,7 +1818,9 @@ namespace Barotrauma
         public static bool HasDivingMask(Character character, float conditionPercentage = 0, bool requireOxygenTank = true) 
             => HasItem(character, Tags.LightDivingGear, out _, requireOxygenTank ? Tags.OxygenSource : Identifier.Empty, conditionPercentage, requireEquipped: true);
 
-        private static List<Item> matchingItems = new List<Item>();
+        // ThreadLocal to ensure thread safety - each thread gets its own list instance
+        private static readonly ThreadLocal<List<Item>> matchingItemsLocal = new ThreadLocal<List<Item>>(() => new List<Item>());
+        private static List<Item> matchingItems => matchingItemsLocal.Value;
 
         /// <summary>
         /// Note: uses a single list for matching items. The item is reused each time when the method is called. So if you use the method twice, and then refer to the first items, you'll actually get the second. 
@@ -1825,15 +1828,16 @@ namespace Barotrauma
         /// </summary>
         public static bool HasItem(Character character, Identifier tagOrIdentifier, out IEnumerable<Item> items, Identifier containedTag = default, float conditionPercentage = 0, bool requireEquipped = false, bool recursive = true, Func<Item, bool> predicate = null)
         {
-            matchingItems.Clear();
+            var localMatchingItems = matchingItems;
-            items = matchingItems;
+            localMatchingItems.Clear();
+            items = localMatchingItems;
             if (character?.Inventory == null) { return false; }
-            matchingItems = character.Inventory.FindAllItems(i => (i.Prefab.Identifier == tagOrIdentifier || i.HasTag(tagOrIdentifier)) &&
+            character.Inventory.FindAllItems(i => (i.Prefab.Identifier == tagOrIdentifier || i.HasTag(tagOrIdentifier)) &&
                 i.ConditionPercentage >= conditionPercentage &&
                 (!requireEquipped || character.HasEquippedItem(i)) &&
-                (predicate == null || predicate(i)), recursive, matchingItems);
+                (predicate == null || predicate(i)), recursive, localMatchingItems);
-            items = matchingItems;
+            items = localMatchingItems;
-            foreach (var item in matchingItems)
+            foreach (var item in localMatchingItems)
             {
                 if (item == null) { continue; }
 

Barotrauma/BarotraumaShared/SharedSource/Characters/AI/NPCConversation.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using Barotrauma.IO;
 using System.Linq;
@@ -9,7 +10,8 @@ namespace Barotrauma
 {
     class NPCConversationCollection : Prefab
     {
-        public static readonly Dictionary<LanguageIdentifier, PrefabCollection<NPCConversationCollection>> Collections = new Dictionary<LanguageIdentifier, PrefabCollection<NPCConversationCollection>>();
+        // Thread-safe dictionary for language-based collections
+        public static readonly ConcurrentDictionary<LanguageIdentifier, PrefabCollection<NPCConversationCollection>> Collections = new ConcurrentDictionary<LanguageIdentifier, PrefabCollection<NPCConversationCollection>>();
 
         public readonly LanguageIdentifier Language;
 
@@ -160,7 +162,24 @@ namespace Barotrauma
             return currentFlags;
         }
 
-        private static readonly List<NPCConversation> previousConversations = new List<NPCConversation>();
+        // Thread-safe previous conversations tracking using copy-on-write pattern
+        private static volatile List<NPCConversation> _previousConversations = new List<NPCConversation>();
+        private static readonly object _previousConversationsLock = new object();
+        private static List<NPCConversation> previousConversations => _previousConversations;
+        
+        private static void AddToPreviousConversations(NPCConversation conversation)
+        {
+            lock (_previousConversationsLock)
+            {
+                var newList = new List<NPCConversation>(_previousConversations);
+                newList.Insert(0, conversation);
+                if (newList.Count > MaxPreviousConversations)
+                {
+                    newList.RemoveAt(MaxPreviousConversations);
+                }
+                _previousConversations = newList;
+            }
+        }
         
         public static List<(Character speaker, string line)> CreateRandom(List<Character> availableSpeakers)
         {
@@ -281,8 +300,7 @@ namespace Barotrauma
 
             if (baseConversation == null)
             {
-                previousConversations.Insert(0, selectedConversation);
+                AddToPreviousConversations(selectedConversation);
-                if (previousConversations.Count > MaxPreviousConversations) previousConversations.RemoveAt(MaxPreviousConversations);
             }
             lineList.Add((speaker, selectedConversation.Line));
             CreateConversation(availableSpeakers, assignedSpeakers, selectedConversation, lineList, availableConversations);

Barotrauma/BarotraumaShared/SharedSource/Characters/AI/Objectives/AIObjectiveFindThieves.cs

@@ -1,5 +1,6 @@
 #nullable enable
 using Microsoft.Xna.Framework;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using Barotrauma.Items.Components;
@@ -68,8 +69,9 @@ namespace Barotrauma
 
         /// <summary>
         /// When did the character last inspect whether some other character has stolen items on them?
+        /// Thread-safe dictionary for concurrent access.
         /// </summary>
-        private static readonly Dictionary<Character, double> lastInspectionTimes = new Dictionary<Character, double>();
+        private static readonly ConcurrentDictionary<Character, double> lastInspectionTimes = new ConcurrentDictionary<Character, double>();
         
         private const float NormalInspectionInterval = 120.0f;
         private const float CriminalInspectionInterval = 30.0f;

Barotrauma/BarotraumaShared/SharedSource/Characters/Animation/Ragdoll.cs

@@ -5,8 +5,10 @@ using FarseerPhysics.Dynamics.Contacts;
 using FarseerPhysics.Dynamics.Joints;
 using Microsoft.Xna.Framework;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 using System.Xml.Linq;
 using Barotrauma.Extensions;
 using LimbParams = Barotrauma.RagdollParams.LimbParams;
@@ -25,7 +27,33 @@ namespace Barotrauma
         /// </summary>
         const float MaxImpactDamage = 0.1f;
 
-        private static readonly List<Ragdoll> list = new List<Ragdoll>();
+        // Thread-safe list using copy-on-write pattern (ConcurrentBag doesn't support indexer/Remove)
+        private static volatile List<Ragdoll> _list = new List<Ragdoll>();
+        private static readonly object _listLock = new object();
+        private static List<Ragdoll> list => _list;
+        
+        private static void ListAdd(Ragdoll ragdoll)
+        {
+            lock (_listLock)
+            {
+                var newList = new List<Ragdoll>(_list) { ragdoll };
+                Interlocked.Exchange(ref _list, newList);
+            }
+        }
+        
+        private static bool ListRemove(Ragdoll ragdoll)
+        {
+            lock (_listLock)
+            {
+                var newList = new List<Ragdoll>(_list);
+                bool removed = newList.Remove(ragdoll);
+                if (removed)
+                {
+                    Interlocked.Exchange(ref _list, newList);
+                }
+                return removed;
+            }
+        }
 
         struct Impact
         {
@@ -45,7 +73,8 @@ namespace Barotrauma
             }
         }
 
-        private readonly Queue<Impact> impactQueue = new Queue<Impact>();
+        // Thread-safe queue for physics collision callbacks
+        private readonly ConcurrentQueue<Impact> impactQueue = new ConcurrentQueue<Impact>();
 
         protected Hull currentHull;
 
@@ -467,7 +496,7 @@ namespace Barotrauma
 
         public Ragdoll(Character character, string seed, RagdollParams ragdollParams = null)
         {
-            list.Add(this);
+            ListAdd(this);
             this.character = character;
             Recreate(ragdollParams ?? RagdollParams);
         }
@@ -744,10 +773,7 @@ namespace Barotrauma
             {
                 if (!f2.IsSensor)
                 {
-                    lock (impactQueue)
+                    impactQueue.Enqueue(new Impact(f1, f2, contact, velocity));
-                    {
-                        impactQueue.Enqueue(new Impact(f1, f2, contact, velocity));
-                    }
                 }
                 return true;
             }
@@ -819,10 +845,7 @@ namespace Barotrauma
                 }
             }
 
-            lock (impactQueue)
+            impactQueue.Enqueue(new Impact(f1, f2, contact, velocity));
-            {
-                impactQueue.Enqueue(new Impact(f1, f2, contact, velocity));
-            }
 
             return true;
         }
@@ -1274,9 +1297,8 @@ namespace Barotrauma
         {
             if (!character.Enabled || character.Removed || Frozen || Invalid || Collider == null || Collider.Removed) { return; }
 
-            while (impactQueue.Count > 0)
+            while (impactQueue.TryDequeue(out var impact))
             {
-                var impact = impactQueue.Dequeue();
                 ApplyImpact(impact.F1, impact.F2, impact.LocalNormal, impact.ImpactPos, impact.Velocity);
             }
 
@@ -2325,7 +2347,7 @@ namespace Barotrauma
                 LimbJoints = null;
             }
 
-            list.Remove(this);
+            ListRemove(this);
         }
 
         public static void RemoveAll()

Barotrauma/BarotraumaShared/SharedSource/Characters/Character.cs

@@ -7,10 +7,12 @@ using FarseerPhysics;
 using FarseerPhysics.Dynamics;
 using Microsoft.Xna.Framework;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Linq;
+using System.Threading;
 using System.Xml.Linq;
 #if SERVER
 using System.Text;
@@ -28,12 +30,70 @@ namespace Barotrauma
 
     public readonly record struct TalentResistanceIdentifier(Identifier ResistanceIdentifier, Identifier TalentIdentifier);
 
+    /// <summary>
+    /// Thread-safe wrapper for character list operations.
+    /// Provides lock-free read operations and synchronized write operations.
+    /// </summary>
+    class ThreadSafeCharacterList : IEnumerable<Character>
+    {
+        private volatile List<Character> _list = new List<Character>();
+        private readonly object _writeLock = new object();
+
+        public int Count => _list.Count;
+
+        public void Add(Character character)
+        {
+            lock (_writeLock)
+            {
+                var newList = new List<Character>(_list) { character };
+                Interlocked.Exchange(ref _list, newList);
+            }
+        }
+
+        public bool Remove(Character character)
+        {
+            lock (_writeLock)
+            {
+                var newList = new List<Character>(_list);
+                bool removed = newList.Remove(character);
+                if (removed)
+                {
+                    Interlocked.Exchange(ref _list, newList);
+                }
+                return removed;
+            }
+        }
+
+        public void Clear()
+        {
+            Interlocked.Exchange(ref _list, new List<Character>());
+        }
+
+        public bool Contains(Character character) => _list.Contains(character);
+
+        public Character this[int index] => _list[index];
+
+        public IEnumerator<Character> GetEnumerator() => _list.GetEnumerator();
+        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => GetEnumerator();
+
+        // LINQ-friendly snapshot for complex queries
+        public List<Character> ToList() => new List<Character>(_list);
+        
+        public Character FirstOrDefault(Func<Character, bool> predicate) => _list.FirstOrDefault(predicate);
+        public Character Find(Predicate<Character> predicate) => _list.Find(predicate);
+        public List<Character> FindAll(Predicate<Character> predicate) => _list.FindAll(predicate);
+        public IEnumerable<Character> Where(Func<Character, bool> predicate) => _list.Where(predicate);
+        public bool Any(Func<Character, bool> predicate) => _list.Any(predicate);
+        public bool None(Func<Character, bool> predicate) => !_list.Any(predicate);
+        public int CountWhere(Func<Character, bool> predicate) => _list.Count(predicate);
+    }
+
     partial class Character : Entity, IDamageable, ISerializableEntity, IClientSerializable, IServerPositionSync
     {
-        public static readonly List<Character> CharacterList = new List<Character>();
+        public static readonly ThreadSafeCharacterList CharacterList = new ThreadSafeCharacterList();
 
         public static int CharacterUpdateInterval = 1;
-        private static int characterUpdateTick = 1;
+        private static volatile int characterUpdateTick = 1;
         
         public const float MaxHighlightDistance = 150.0f;
         public const float MaxDragDistance = 200.0f;

Barotrauma/BarotraumaShared/SharedSource/Characters/Health/CharacterHealth.cs

@@ -3,15 +3,13 @@ using Barotrauma.Extensions;
 using Barotrauma.Networking;
 using Microsoft.Xna.Framework;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using System.Threading;
 using System.Xml.Linq;
-using Barotrauma.Networking;
-using Barotrauma.Extensions;
-using System.Globalization;
 using MoonSharp.Interpreter;
-using Barotrauma.Abilities;
 
 namespace Barotrauma
 {
@@ -132,8 +130,9 @@ namespace Barotrauma
 
         private readonly List<LimbHealth> limbHealths = new List<LimbHealth>();
 
-        private readonly Dictionary<Affliction, LimbHealth> afflictions = new Dictionary<Affliction, LimbHealth>();
+        // Thread-safe afflictions dictionary for concurrent access
-        private readonly HashSet<Affliction> irremovableAfflictions = new HashSet<Affliction>();
+        private readonly ConcurrentDictionary<Affliction, LimbHealth> afflictions = new ConcurrentDictionary<Affliction, LimbHealth>();
+        private readonly ConcurrentDictionary<Affliction, byte> irremovableAfflictions = new ConcurrentDictionary<Affliction, byte>();
         private Affliction bloodlossAffliction;
         private Affliction oxygenLowAffliction;
         private Affliction pressureAffliction;
@@ -324,13 +323,13 @@ namespace Barotrauma
 
         private void InitIrremovableAfflictions()
         {
-            irremovableAfflictions.Add(bloodlossAffliction = new Affliction(AfflictionPrefab.Bloodloss, 0.0f));
+            irremovableAfflictions.TryAdd(bloodlossAffliction = new Affliction(AfflictionPrefab.Bloodloss, 0.0f), 0);
-            irremovableAfflictions.Add(stunAffliction = new Affliction(AfflictionPrefab.Stun, 0.0f));
+            irremovableAfflictions.TryAdd(stunAffliction = new Affliction(AfflictionPrefab.Stun, 0.0f), 0);
-            irremovableAfflictions.Add(pressureAffliction = new Affliction(AfflictionPrefab.Pressure, 0.0f));
+            irremovableAfflictions.TryAdd(pressureAffliction = new Affliction(AfflictionPrefab.Pressure, 0.0f), 0);
-            irremovableAfflictions.Add(oxygenLowAffliction = new Affliction(AfflictionPrefab.OxygenLow, 0.0f));
+            irremovableAfflictions.TryAdd(oxygenLowAffliction = new Affliction(AfflictionPrefab.OxygenLow, 0.0f), 0);
-            foreach (Affliction affliction in irremovableAfflictions)
+            foreach (Affliction affliction in irremovableAfflictions.Keys)
             {
-                afflictions.Add(affliction, null);
+                afflictions.TryAdd(affliction, null);
             }
         }
 
@@ -338,7 +337,7 @@ namespace Barotrauma
 
         public IReadOnlyCollection<Affliction> GetAllAfflictions()
         {
-            return afflictions.Keys;
+            return afflictions.Keys.ToList();
         }
 
         public IEnumerable<Affliction> GetAllAfflictions(Func<Affliction, bool> limbHealthFilter)
@@ -503,19 +502,18 @@ namespace Barotrauma
         /// </summary>
         public float GetResistance(AfflictionPrefab afflictionPrefab, LimbType limbType)
         {
-            lock (afflictions) {
+            // ConcurrentDictionary is thread-safe, no lock needed
-                // This is a % resistance (0 to 1.0)
+            // This is a % resistance (0 to 1.0)
-                float resistance = 0.0f;
+            float resistance = 0.0f;
-                foreach (KeyValuePair<Affliction, LimbHealth> kvp in afflictions)
+            foreach (KeyValuePair<Affliction, LimbHealth> kvp in afflictions)
-                {
+            {
-                    var affliction = kvp.Key;
+                var affliction = kvp.Key;
-                    resistance += affliction.GetResistance(afflictionPrefab.Identifier, limbType);
+                resistance += affliction.GetResistance(afflictionPrefab.Identifier, limbType);
-                }
-                // This is a multiplier, ie. 0.0 = 100% resistance and 1.0 = 0% resistance
-                float abilityResistanceMultiplier = Character.GetAbilityResistance(afflictionPrefab);
-                // The returned value is calculated to be a % resistance again
-                return 1 - ((1 - resistance) * abilityResistanceMultiplier);
             }
+            // This is a multiplier, ie. 0.0 = 100% resistance and 1.0 = 0% resistance
+            float abilityResistanceMultiplier = Character.GetAbilityResistance(afflictionPrefab);
+            // The returned value is calculated to be a % resistance again
+            return 1 - ((1 - resistance) * abilityResistanceMultiplier);
         }
 
         public float GetStatValue(StatTypes statType)
@@ -696,14 +694,14 @@ namespace Barotrauma
                     a.Prefab.AfflictionType == AfflictionPrefab.Bleeding.AfflictionType));
             foreach (var affliction in afflictionsToRemove)
             {
-                afflictions.Remove(affliction);
+                afflictions.TryRemove(affliction, out _);
             }
 
             foreach (LimbHealth limbHealth in limbHealths)
             {
-                if (damageAmount > 0.0f) { afflictions.Add(AfflictionPrefab.InternalDamage.Instantiate(damageAmount), limbHealth); }
+                if (damageAmount > 0.0f) { afflictions.TryAdd(AfflictionPrefab.InternalDamage.Instantiate(damageAmount), limbHealth); }
-                if (bleedingDamageAmount > 0.0f && DoesBleed) { afflictions.Add(AfflictionPrefab.Bleeding.Instantiate(bleedingDamageAmount), limbHealth); }
+                if (bleedingDamageAmount > 0.0f && DoesBleed) { afflictions.TryAdd(AfflictionPrefab.Bleeding.Instantiate(bleedingDamageAmount), limbHealth); }
-                if (burnDamageAmount > 0.0f) { afflictions.Add(AfflictionPrefab.Burn.Instantiate(burnDamageAmount), limbHealth); }
+                if (burnDamageAmount > 0.0f) { afflictions.TryAdd(AfflictionPrefab.Burn.Instantiate(burnDamageAmount), limbHealth); }
             }
             
             RecalculateVitality();
@@ -743,7 +741,7 @@ namespace Barotrauma
             afflictionsToRemove.AddRange(afflictions.Keys.Where(affliction => predicate(affliction)));
             foreach (var affliction in afflictionsToRemove)
             {
-                afflictions.Remove(affliction);
+                afflictions.TryRemove(affliction, out _);
             }
             CalculateVitality();
         }
@@ -751,14 +749,14 @@ namespace Barotrauma
         public void RemoveAllAfflictions()
         {
             afflictionsToRemove.Clear();
-            afflictionsToRemove.AddRange(afflictions.Keys.Where(a => !irremovableAfflictions.Contains(a))); 
+            afflictionsToRemove.AddRange(afflictions.Keys.Where(a => !irremovableAfflictions.ContainsKey(a))); 
             foreach (var affliction in afflictionsToRemove)
             {
                 //set strength to 0 in case the affliction needs to react to becoming inactive
                 affliction.Strength = 0.0f;
-                afflictions.Remove(affliction);
+                afflictions.TryRemove(affliction, out _);
             }
-            foreach (Affliction affliction in irremovableAfflictions)
+            foreach (Affliction affliction in irremovableAfflictions.Keys)
             {
                 affliction.Strength = 0.0f;
             }
@@ -769,15 +767,15 @@ namespace Barotrauma
         {
             afflictionsToRemove.Clear();
             afflictionsToRemove.AddRange(afflictions.Keys.Where(a => 
-                !irremovableAfflictions.Contains(a) && 
+                !irremovableAfflictions.ContainsKey(a) && 
                 !a.Prefab.IsBuff && 
                 a.Prefab.AfflictionType != "geneticmaterialbuff" && 
                 a.Prefab.AfflictionType != "geneticmaterialdebuff"));
             foreach (var affliction in afflictionsToRemove)
             {
-                afflictions.Remove(affliction);
+                afflictions.TryRemove(affliction, out _);
             }
-            foreach (Affliction affliction in irremovableAfflictions)
+            foreach (Affliction affliction in irremovableAfflictions.Keys)
             {
                 affliction.Strength = 0.0f;
             }
@@ -869,7 +867,7 @@ namespace Barotrauma
             var copyAffliction = newAffliction.Prefab.Instantiate(
                 Math.Min(newAffliction.Prefab.MaxStrength, newAffliction.Strength * (100.0f / MaxVitality) * (1f - GetResistance(newAffliction.Prefab, limbType))),
                 newAffliction.Source);
-            afflictions.Add(copyAffliction, limbHealth);
+            afflictions.TryAdd(copyAffliction, limbHealth);
             AchievementManager.OnAfflictionReceived(copyAffliction, Character);
             MedicalClinic.OnAfflictionCountChanged(Character);
 
@@ -914,7 +912,7 @@ namespace Barotrauma
                     if (affliction.Strength <= 0.0f)
                     {
                         AchievementManager.OnAfflictionRemoved(affliction, Character);
-                        if (!irremovableAfflictions.Contains(affliction)) { afflictionsToRemove.Add(affliction); }
+                        if (!irremovableAfflictions.ContainsKey(affliction)) { afflictionsToRemove.Add(affliction); }
                         continue;
                     }
                     if (affliction.Prefab.Duration > 0.0f)
@@ -952,7 +950,7 @@ namespace Barotrauma
 
                 foreach (var affliction in afflictionsToRemove)
                 {
-                    afflictions.Remove(affliction);
+                    afflictions.TryRemove(affliction, out _);
                 }
 
                 if (afflictionsToRemove.Count is not 0)
@@ -1519,14 +1517,14 @@ namespace Barotrauma
                 }
                 if (afflictionPredicate != null && !afflictionPredicate.Invoke(afflictionPrefab)) { return; }
                 float strength = afflictionElement.GetAttributeFloat("strength", 0.0f);
-                var irremovableAffliction = irremovableAfflictions.FirstOrDefault(a => a.Prefab == afflictionPrefab);
+                var irremovableAffliction = irremovableAfflictions.Keys.FirstOrDefault(a => a.Prefab == afflictionPrefab);
                 if (irremovableAffliction != null)
                 {
                     irremovableAffliction.Strength = strength;
                 }
                 else
                 {
-                    afflictions.Add(afflictionPrefab.Instantiate(strength), limbHealth);
+                    afflictions.TryAdd(afflictionPrefab.Instantiate(strength), limbHealth);
                 }
             }
         }

Barotrauma/BarotraumaShared/SharedSource/Characters/Params/Animation/AnimationParams.cs

@@ -1,10 +1,12 @@
 using Microsoft.Xna.Framework;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Globalization;
 using Barotrauma.IO;
 using System;
 using System.Diagnostics;
 using System.Linq;
+using System.Threading;
 using System.Xml.Linq;
 using Barotrauma.Extensions;
 
@@ -117,8 +119,9 @@ namespace Barotrauma
         public virtual AnimationType AnimationType { get; protected set; }
         /// <summary>
         /// The cached animations of all the characters that have been loaded.
+        /// Thread-safe cache using ConcurrentDictionary.
         /// </summary>
-        private static readonly Dictionary<Identifier, Dictionary<string, AnimationParams>> allAnimations = new Dictionary<Identifier, Dictionary<string, AnimationParams>>();
+        private static readonly ConcurrentDictionary<Identifier, ConcurrentDictionary<string, AnimationParams>> allAnimations = new ConcurrentDictionary<Identifier, ConcurrentDictionary<string, AnimationParams>>();
 
         [Header("Movement")]
         [Serialize(1.0f, IsPropertySaveable.Yes), Editable(DecimalCount = 2, MinValueFloat = 0, MaxValueFloat = Ragdoll.MAX_SPEED, ValueStep = 0.1f)]
@@ -244,7 +247,9 @@ namespace Barotrauma
             return GetAnimParams<T>(speciesName, animSpecies, fallbackSpecies: character.Prefab.GetBaseCharacterSpeciesName(speciesName), animType, file, throwErrors);
         }
         
-        private static readonly List<string> errorMessages = new List<string>();
+        // ThreadLocal for thread-safe error message collection during animation loading
+        private static readonly ThreadLocal<List<string>> errorMessagesLocal = new ThreadLocal<List<string>>(() => new List<string>());
+        private static List<string> errorMessages => errorMessagesLocal.Value;
 
         private static T GetAnimParams<T>(Identifier speciesName, Identifier animSpecies, Identifier fallbackSpecies, AnimationType animType, Either<string, ContentPath> file, bool throwErrors = true) where T : AnimationParams, new()
         {
@@ -262,11 +267,7 @@ namespace Barotrauma
             }
             ContentPackage contentPackage = contentPath?.ContentPackage ?? CharacterPrefab.FindBySpeciesName(speciesName)?.ContentPackage;
             Debug.Assert(contentPackage != null);
-            if (!allAnimations.TryGetValue(speciesName, out Dictionary<string, AnimationParams> animations))
+            var animations = allAnimations.GetOrAdd(speciesName, _ => new ConcurrentDictionary<string, AnimationParams>());
-            {
-                animations = new Dictionary<string, AnimationParams>();
-                allAnimations.Add(speciesName, animations);
-            }
             string key = fileName ?? contentPath?.Value ?? GetDefaultFileName(animSpecies, animType);
             if (animations.TryGetValue(key, out AnimationParams anim) && anim.AnimationType == animType)
             {
@@ -418,16 +419,12 @@ namespace Barotrauma
             {
                 throw new Exception("Cannot create an animation file of type " + animationType);
             }
-            if (!allAnimations.TryGetValue(speciesName, out Dictionary<string, AnimationParams> anims))
+            var anims = allAnimations.GetOrAdd(speciesName, _ => new ConcurrentDictionary<string, AnimationParams>());
-            {
-                anims = new Dictionary<string, AnimationParams>();
-                allAnimations.Add(speciesName, anims);
-            }
             string fileName = IO.Path.GetFileNameWithoutExtension(fullPath);
             if (anims.ContainsKey(fileName))
             {
                 DebugConsole.NewMessage($"[AnimationParams] Removing the old animation of type {animationType}.", Color.Red);
-                anims.Remove(fileName);
+                anims.TryRemove(fileName, out _);
             }
             var instance = new T();
             XElement animationElement = new XElement(GetDefaultFileName(speciesName, animationType), new XAttribute("animationtype", animationType.ToString()));
@@ -439,7 +436,7 @@ namespace Barotrauma
             instance.IsLoaded = instance.Deserialize(animationElement);
             instance.Save();
             instance.Load(contentPath, speciesName);
-            anims.Add(fileName, instance);
+            anims.TryAdd(fileName, instance);
             DebugConsole.NewMessage($"[AnimationParams] New animation file of type {animationType} created.", Color.GhostWhite);
             return instance;
         }
@@ -467,17 +464,14 @@ namespace Barotrauma
             {
                 // Update the key by removing and re-adding the animation.
                 string fileName = FileNameWithoutExtension;
-                if (allAnimations.TryGetValue(SpeciesName, out Dictionary<string, AnimationParams> animations))
+                if (allAnimations.TryGetValue(SpeciesName, out ConcurrentDictionary<string, AnimationParams> animations))
                 {
-                    animations.Remove(fileName);
+                    animations.TryRemove(fileName, out _);
                 }
                 base.UpdatePath(newPath);
                 if (animations != null)
                 {
-                    if (!animations.ContainsKey(fileName))
+                    animations.TryAdd(fileName, this);
-                    {
-                        animations.Add(fileName, this);
-                    }
                 }
             }
         }

Barotrauma/BarotraumaShared/SharedSource/Characters/Params/Ragdoll/RagdollParams.cs

@@ -1,5 +1,6 @@
 using Microsoft.Xna.Framework;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Xml.Linq;
@@ -124,8 +125,9 @@ namespace Barotrauma
         /// key1: Species name
         /// key2: File path
         /// value: Ragdoll parameters
+        /// Thread-safe cache using ConcurrentDictionary.
         /// </summary>
-        private static readonly Dictionary<Identifier, Dictionary<string, RagdollParams>> allRagdolls = new Dictionary<Identifier, Dictionary<string, RagdollParams>>();
+        private static readonly ConcurrentDictionary<Identifier, ConcurrentDictionary<string, RagdollParams>> allRagdolls = new ConcurrentDictionary<Identifier, ConcurrentDictionary<string, RagdollParams>>();
 
         public List<ColliderParams> Colliders { get; private set; } = new List<ColliderParams>();
         public List<LimbParams> Limbs { get; private set; } = new List<LimbParams>();
@@ -222,11 +224,7 @@ namespace Barotrauma
                 Debug.Assert(!fileName.IsNullOrWhiteSpace() || !contentPath.IsNullOrWhiteSpace());
             }
             Debug.Assert(contentPackage != null);
-            if (!allRagdolls.TryGetValue(speciesName, out Dictionary<string, RagdollParams> ragdolls))
+            var ragdolls = allRagdolls.GetOrAdd(speciesName, _ => new ConcurrentDictionary<string, RagdollParams>());
-            {
-                ragdolls = new Dictionary<string, RagdollParams>();
-                allRagdolls.Add(speciesName, ragdolls);
-            }
             string key = fileName ?? contentPath?.Value ?? GetDefaultFileName(ragdollSpecies);
             if (ragdolls.TryGetValue(key, out RagdollParams ragdoll))
             {
@@ -331,10 +329,10 @@ namespace Barotrauma
             if (allRagdolls.ContainsKey(speciesName))
             {
                 DebugConsole.NewMessage($"[RagdollParams] Removing the old ragdolls from {speciesName}.", Color.Red);
-                allRagdolls.Remove(speciesName);
+                allRagdolls.TryRemove(speciesName, out _);
             }
-            var ragdolls = new Dictionary<string, RagdollParams>();
+            var ragdolls = new ConcurrentDictionary<string, RagdollParams>();
-            allRagdolls.Add(speciesName, ragdolls);
+            allRagdolls.TryAdd(speciesName, ragdolls);
             var instance = new T
             {
                 doc = new XDocument(mainElement)
@@ -345,7 +343,7 @@ namespace Barotrauma
             instance.IsLoaded = instance.Deserialize(mainElement);
             instance.Save();
             instance.Load(contentPath, speciesName);
-            ragdolls.Add(instance.FileNameWithoutExtension, instance);
+            ragdolls.TryAdd(instance.FileNameWithoutExtension, instance);
             DebugConsole.NewMessage("[RagdollParams] New default ragdoll params successfully created at " + fullPath, Color.NavajoWhite);
             return instance;
         }
@@ -362,17 +360,14 @@ namespace Barotrauma
             {
                 // Update the key by removing and re-adding the ragdoll.
                 string fileName = FileNameWithoutExtension;
-                if (allRagdolls.TryGetValue(SpeciesName, out Dictionary<string, RagdollParams> ragdolls))
+                if (allRagdolls.TryGetValue(SpeciesName, out ConcurrentDictionary<string, RagdollParams> ragdolls))
                 {
-                    ragdolls.Remove(fileName);
+                    ragdolls.TryRemove(fileName, out _);
                 }
                 base.UpdatePath(fullPath);
                 if (ragdolls != null)
                 {
-                    if (!ragdolls.ContainsKey(fileName))
+                    ragdolls.TryAdd(fileName, this);
-                    {
-                        ragdolls.Add(fileName, this);
-                    }
                 }
             }
         }

Barotrauma/BarotraumaShared/SharedSource/Characters/Talents/CharacterTalent.cs

@@ -1,6 +1,8 @@
 using Barotrauma.Abilities;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Threading;
 
 namespace Barotrauma
 {
@@ -72,7 +74,9 @@ namespace Barotrauma
             }
         }
 
-        private static readonly HashSet<Identifier> checkedNonStackableTalents = new();
+        // ThreadLocal for thread-safe talent checking
+        private static readonly ThreadLocal<HashSet<Identifier>> checkedNonStackableTalentsLocal = new ThreadLocal<HashSet<Identifier>>(() => new HashSet<Identifier>());
+        private static HashSet<Identifier> checkedNonStackableTalents => checkedNonStackableTalentsLocal.Value;
 
         /// <summary>
         /// Checks talents for a given AbilityObject taking into account non-stackable talents.

Barotrauma/BarotraumaShared/SharedSource/ContentManagement/ContentFile/NPCConversationsFile.cs

@@ -1,4 +1,4 @@
-using System.Xml.Linq;
+using System.Xml.Linq;
 
 namespace Barotrauma
 {
@@ -21,7 +21,7 @@ namespace Barotrauma
             var npcConversationCollection = new NPCConversationCollection(this, mainElement);
             if (!NPCConversationCollection.Collections.ContainsKey(npcConversationCollection.Language))
             {
-                NPCConversationCollection.Collections.Add(npcConversationCollection.Language, new PrefabCollection<NPCConversationCollection>());
+                NPCConversationCollection.Collections.TryAdd(npcConversationCollection.Language, new PrefabCollection<NPCConversationCollection>());
             }
             NPCConversationCollection.Collections[npcConversationCollection.Language].Add(npcConversationCollection, allowOverriding);
         }

Barotrauma/BarotraumaShared/SharedSource/Items/Components/Signal/DelayComponent.cs

@@ -1,6 +1,8 @@
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Globalization;
+using System.Linq;
 using System.Xml.Linq;
 using Microsoft.Xna.Framework;
 namespace Barotrauma.Items.Components
@@ -25,7 +27,8 @@ namespace Barotrauma.Items.Components
         private int signalQueueSize;
         private int delayTicks;
 
-        private readonly Queue<DelayedSignal> signalQueue = new Queue<DelayedSignal>();
+        // Thread-safe queue for concurrent access
+        private readonly ConcurrentQueue<DelayedSignal> signalQueue = new ConcurrentQueue<DelayedSignal>();
 
         private DelayedSignal prevQueuedSignal;
         
@@ -40,7 +43,8 @@ namespace Barotrauma.Items.Components
                 delay = value;
                 delayTicks = (int)(delay / Timing.Step);
                 signalQueueSize = Math.Max(delayTicks, 1) * 2;
-                signalQueue.Clear();
+                // ConcurrentQueue doesn't have Clear(), drain it instead
+                while (signalQueue.TryDequeue(out _)) { }
             }
         }
 
@@ -66,19 +70,19 @@ namespace Barotrauma.Items.Components
 
         public override void Update(float deltaTime, Camera cam)
         {
-            if (signalQueue.Count == 0)
+            if (signalQueue.IsEmpty)
             {
                 IsActive = false;
                 return;
             }
 
-            foreach (var val in signalQueue)
+            // Use ToArray() snapshot for thread-safe iteration
+            foreach (var val in signalQueue.ToArray())
             {
                 val.SendTimer -= 1;
             }
-            while (signalQueue.Count > 0 && signalQueue.Peek().SendTimer <= 0)
+            while (signalQueue.TryPeek(out var signalOut) && signalOut.SendTimer <= 0)
             {
-                var signalOut = signalQueue.Peek();
                 signalOut.SendDuration -= 1;
                 item.SendSignal(new Signal(signalOut.Signal.value, sender: signalOut.Signal.sender, strength: signalOut.Signal.strength), "signal_out");
                 if (signalOut.SendDuration <= 0) 
@@ -100,11 +104,15 @@ namespace Barotrauma.Items.Components
             {
                 case "signal_in":
                     if (signalQueue.Count >= signalQueueSize) { return; }
-                    if (ResetWhenSignalReceived) { prevQueuedSignal = null; signalQueue.Clear(); }
+                    if (ResetWhenSignalReceived) 
-                    if (ResetWhenDifferentSignalReceived && signalQueue.Count > 0 && signalQueue.Peek().Signal.value != signal.value)
                     { 
                         prevQueuedSignal = null; 
-                        signalQueue.Clear();
+                        while (signalQueue.TryDequeue(out _)) { } 
+                    }
+                    if (ResetWhenDifferentSignalReceived && signalQueue.TryPeek(out var peekSignal) && peekSignal.Signal.value != signal.value)
+                    {
+                        prevQueuedSignal = null;
+                        while (signalQueue.TryDequeue(out _)) { }
                     }
 
                     if (prevQueuedSignal != null && 
@@ -127,10 +135,10 @@ namespace Barotrauma.Items.Components
                     if (float.TryParse(signal.value, NumberStyles.Any, CultureInfo.InvariantCulture, out float newDelay))
                     {
 						newDelay = MathHelper.Clamp(newDelay, 0, 60);
-                        if (signalQueue.Count > 0 && newDelay != Delay)
+                        if (!signalQueue.IsEmpty && newDelay != Delay)
                         {
                             prevQueuedSignal = null;
-                            signalQueue.Clear();
+                            while (signalQueue.TryDequeue(out _)) { }
                         }
                         Delay = newDelay;
                     }