Reapply "OBT1.1.0 Merge branch 'dev_pte' into dev"

This reverts commit 046483b9da.

Barotrauma/BarotraumaShared/SharedSource/Physics/PhysicsBodyQueue.cs

@@ -0,0 +1,155 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+
+namespace Barotrauma
+{
+    /// <summary>
+    /// Thread-safe queue for deferring physics operations to the main thread.
+    /// This is necessary because Farseer Physics' DynamicTree is not thread-safe,
+    /// and physics operations cannot be safely performed during parallel updates.
+    /// 
+    /// Supported operations include:
+    /// - Physics body creation
+    /// - Physics body transform updates (SetTransform, SetTransformIgnoreContacts)
+    /// - Any other operation that modifies the Farseer physics world
+    /// </summary>
+/// <start>
+///  ├─> PhysicsBodyQueue.IsInParallelContext = true (ThreadStatic)
+///  ├─> Item.Update()
+///  │     └─> StatusEffect.Apply()
+///  │           └─> Character.Kill()
+///  │                 └─> Item.Drop()
+///  │                       └─> Check if IsInParallelContext == true
+///  │                             └─> PhysicsBodyQueue.Enqueue(Physics operation)
+///  ├──> PhysicsBodyQueue.IsInParallelContext = false
+///  └──> PhysicsBodyQueue.ProcessPendingOperations() ← Main thread executes
+///        └─> body.SetTransformIgnoreContacts()
+    static class PhysicsBodyQueue
+    {
+        private static readonly object _lock = new object();
+        private static readonly Queue<Action> _pendingOperations = new Queue<Action>();
+
+        /// <summary>
+        /// Thread-local flag indicating whether the current thread is in a parallel physics update context.
+        /// When true, physics operations should be deferred using this queue instead of executing immediately.
+        /// </summary>
+        [ThreadStatic]
+        private static bool _isInParallelContext;
+
+        /// <summary>
+        /// Gets or sets whether the current thread is in a parallel update context.
+        /// When true, physics operations should be queued instead of executed immediately.
+        /// </summary>
+        public static bool IsInParallelContext
+        {
+            get => _isInParallelContext;
+            set => _isInParallelContext = value;
+        }
+
+        /// <summary>
+        /// Enqueues a physics operation to be executed on the main thread.
+        /// This method is thread-safe and can be called from parallel update loops.
+        /// </summary>
+        /// <param name="operation">The physics operation to defer</param>
+        public static void Enqueue(Action operation)
+        {
+            if (operation == null) { return; }
+            lock (_lock)
+            {
+                _pendingOperations.Enqueue(operation);
+            }
+        }
+
+        /// <summary>
+        /// Enqueues a physics body creation action to be executed on the main thread.
+        /// This method is thread-safe and can be called from parallel update loops.
+        /// </summary>
+        /// <param name="createAction">The action that creates the physics body</param>
+        public static void EnqueueCreation(Action createAction)
+        {
+            Enqueue(createAction);
+        }
+
+        /// <summary>
+        /// Executes a physics operation, either immediately or deferred depending on context.
+        /// If called from a parallel context, the operation will be queued for later execution.
+        /// If called from the main thread (outside parallel loops), the operation executes immediately.
+        /// </summary>
+        /// <param name="operation">The physics operation to execute</param>
+        public static void ExecuteOrDefer(Action operation)
+        {
+            if (operation == null) { return; }
+            
+            if (_isInParallelContext)
+            {
+                Enqueue(operation);
+            }
+            else
+            {
+                operation();
+            }
+        }
+
+        /// <summary>
+        /// Gets the number of pending physics operations.
+        /// </summary>
+        public static int PendingCount
+        {
+            get
+            {
+                lock (_lock)
+                {
+                    return _pendingOperations.Count;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Processes all pending physics operations.
+        /// Must be called on the main thread, outside of any parallel loops.
+        /// </summary>
+        public static void ProcessPendingOperations()
+        {
+            while (true)
+            {
+                Action action;
+                lock (_lock)
+                {
+                    if (_pendingOperations.Count == 0) { break; }
+                    action = _pendingOperations.Dequeue();
+                }
+                try
+                {
+                    action?.Invoke();
+                }
+                catch (Exception e)
+                {
+                    DebugConsole.ThrowError($"Error processing deferred physics operation: {e.Message}", e);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Legacy method for backwards compatibility.
+        /// Calls ProcessPendingOperations().
+        /// </summary>
+        public static void ProcessPendingCreations()
+        {
+            ProcessPendingOperations();
+        }
+
+        /// <summary>
+        /// Clears all pending physics operations.
+        /// Should be called when ending a round or cleaning up.
+        /// </summary>
+        public static void Clear()
+        {
+            lock (_lock)
+            {
+                _pendingOperations.Clear();
+            }
+        }
+    }
+}
+