Fixed multiple LINQ using shared resources and cause crashes

Added an null check in AIObjectiveManager.cs to avoid accessing removed resources
Use shuffledGaps instead of gapList to ensure update order requirement(already in master)
Updated parallelism count

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

@@ -382,8 +382,13 @@ namespace Barotrauma
             }
             steeringBuffer = Math.Clamp(steeringBuffer, minSteeringBuffer, maxSteeringBuffer);
 
-            AnimController.Crouching = shouldCrouch;
+            // in case of somehow AnimController was a null, eg. something removed AnimController in the middle of an update
-            CheckCrouching(deltaTime);
+            if (AnimController != null) 
+            {
+                AnimController.Crouching = shouldCrouch;
+                CheckCrouching(deltaTime);
+            }
+
             Character.ClearInputs();
             
             if (SortTimer > 0.0f)
@@ -1638,7 +1643,8 @@ namespace Barotrauma
             if (mode == AIObjectiveCombat.CombatMode.None) { return; }
             if (Character.IsDead || Character.IsIncapacitated || Character.Removed) { return; }
             if (!Character.IsBot) { return; }
-            if (ObjectiveManager.Objectives.FirstOrDefault(o => o is AIObjectiveCombat) is AIObjectiveCombat combatObjective)
+            List<AIObjective> ObjectivesLocal = ObjectiveManager.Objectives;
+            if (ObjectivesLocal.FirstOrDefault(o => o is AIObjectiveCombat) is AIObjectiveCombat combatObjective)
             {
                 // Don't replace offensive mode with something else
                 if (combatObjective.Mode == AIObjectiveCombat.CombatMode.Offensive && mode != AIObjectiveCombat.CombatMode.Offensive) { return; }

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

@@ -126,7 +126,7 @@ namespace Barotrauma
             }
             else
             {
-                Objectives.RemoveAll(o => o.GetType() == type);
+                Objectives.RemoveAll(o => o?.GetType() == type);
             }
             Objectives.Add(objective);
         }

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

@@ -345,7 +345,8 @@ namespace Barotrauma.Items.Components
             {
                 Connection recipient = wire.OtherConnection(this);
                 if (recipient == null) { continue; }
-                if (recipient.item == this.item || signal.source?.LastSentSignalRecipients.LastOrDefault() == recipient) { continue; }
+                List<Connection> LastSentSignalRecipientsCopy = signal.source?.LastSentSignalRecipients.ToList();
+                if (recipient.item == this.item || LastSentSignalRecipientsCopy.LastOrDefault() == recipient) { continue; }
 
                 signal.source?.LastSentSignalRecipients.Add(recipient);
 #if CLIENT

Barotrauma/BarotraumaShared/SharedSource/Map/MapEntity.cs

@@ -816,7 +816,7 @@ namespace Barotrauma
 
             // Gap update (has order dependencies, keep random order but execute sequentially)
             var shuffledGaps = gapList.OrderBy(g => Rand.Int(int.MaxValue)).ToList();
-            Parallel.ForEach(gapList, parallelOptions, gap =>
+            Parallel.ForEach(shuffledGaps, parallelOptions, gap =>
             {
                 PhysicsBodyQueue.IsInParallelContext = true;
                 try

Barotrauma/BarotraumaShared/SharedSource/Screens/GameScreen.cs

@@ -25,7 +25,7 @@ namespace Barotrauma
 
         private static readonly ParallelOptions parallelOptions = new ParallelOptions
         {
-            MaxDegreeOfParallelism = Environment.ProcessorCount * 2,
+            MaxDegreeOfParallelism = Math.Max(4,Environment.ProcessorCount - 1),
         };
 
 #if CLIENT
@@ -259,33 +259,15 @@ namespace Barotrauma
             Character.Controlled?.UpdateLocalCursor(cam);
 
 #elif SERVER
-            Parallel.Invoke(parallelOptions,
+            // DO NOT PARALLELIZE THESE TWO OR IT MAY STUCK HERE
-                () => 
+            // SO FOLLOW THE ORIGINAL SINGLE-THREAD LOGIC STRICTLY
-                { 
+
-                    PhysicsBodyQueue.IsInParallelContext = true;
+            if (Level.Loaded != null) Level.Loaded.Update((float)deltaTime, Camera.Instance);
-                    try
+
-                    {
+            Character.UpdateAll((float)deltaTime, Camera.Instance);
-                        if (Level.Loaded != null) Level.Loaded.Update((float)deltaTime, Camera.Instance);
+
-                    }
+            StatusEffect.UpdateAll((float)deltaTime);
-                    finally
+
-                    {
-                        PhysicsBodyQueue.IsInParallelContext = false;
-                    }
-                },
-                () => 
-                {
-                    PhysicsBodyQueue.IsInParallelContext = true;
-                    try
-                    {
-                        Character.UpdateAll((float)deltaTime, Camera.Instance);
-                    }
-                    finally
-                    {
-                        PhysicsBodyQueue.IsInParallelContext = false;
-                    }
-                }
-            );
-            
             PhysicsBodyQueue.ProcessPendingOperations();
 #endif
 
@@ -310,8 +292,6 @@ namespace Barotrauma
 
             MapEntity.UpdateAll((float)deltaTime, Camera.Instance, parallelOptions);
 
-            StatusEffect.UpdateAll((float)deltaTime);
-
 #endif
 
 #if CLIENT
@@ -321,6 +301,7 @@ namespace Barotrauma
 #endif
             //Character.UpdateAnimAll is not thread-safe and must be executed on the main thread
             Character.UpdateAnimAll((float)deltaTime);
+            PhysicsBodyQueue.ProcessPendingOperations();
 
 #if CLIENT
             Ragdoll.UpdateAll((float)deltaTime, cam);