Improve object pool safety

Author: oformaniuk

source/Handlebars/Arguments.cs

@@ -322,7 +322,7 @@ public void Dispose()
             private struct Policy : IInternalObjectPoolPolicy<Enumerator>
             {
                 public Enumerator Create() => new Enumerator();
-
+                public bool TryClaim(Enumerator item) => true;
                 public bool Return(Enumerator item)
                 {
                     item.Reset();

source/Handlebars/BindingContext.cs

@@ -17,8 +17,10 @@ public sealed partial class BindingContext : IDisposable, IHelpersRegistry
 
         internal readonly DeferredValue<BindingContext, ObjectDescriptor> Descriptor;
 
-        private BindingContext()
+        private BindingContext(bool claim)
         {
+            _claimed = claim ? 1 : 0;
+            
             InlinePartialTemplates = new CascadeIndex<string, Action<EncodedTextWriter, BindingContext>, StringEqualityComparer>(new StringEqualityComparer(StringComparison.OrdinalIgnoreCase));
             Helpers = new CascadeIndex<string, IHelperDescriptor<HelperOptions>, StringEqualityComparer>(new StringEqualityComparer());
             BlockHelpers = new CascadeIndex<string, IHelperDescriptor<BlockHelperOptions>, StringEqualityComparer>(new StringEqualityComparer());

source/Handlebars/Collections/ImmutableStack.cs

@@ -66,6 +66,7 @@ public override void Write(object value)
         private readonly struct Policy : IInternalObjectPoolPolicy<EncodedTextWriterWrapper>
         {
 	        public EncodedTextWriterWrapper Create() => new EncodedTextWriterWrapper();
+	        public bool TryClaim(EncodedTextWriterWrapper item) => true;
 
 	        public bool Return(EncodedTextWriterWrapper obj)
 	        {

source/Handlebars/IO/EncodedTextWriterWrapper.cs

@@ -40,7 +40,7 @@ public Policy(int initialCapacity, int maximumRetainedCapacity = 4096)
             }
 
             public ReusableStringWriter Create() => new ReusableStringWriter();
-
+            public bool TryClaim(ReusableStringWriter item) => true;
             public bool Return(ReusableStringWriter item) => _policy.Return(item.GetStringBuilder());
         }
     }

source/Handlebars/IO/PolledStringWriter.cs

@@ -66,7 +66,7 @@ public void Dispose()
         private struct Policy : IInternalObjectPoolPolicy<TextEncoderWrapper>
         {
             public TextEncoderWrapper Create() => new TextEncoderWrapper();
-
+            public bool TryClaim(TextEncoderWrapper item) => true;
             public bool Return(TextEncoderWrapper item)
             {
                 item._enabled = true;

source/Handlebars/IO/TextEncoderWrapper.cs

@@ -1,3 +1,4 @@
+using System.Threading;
 using HandlebarsDotNet.Compiler;
 using HandlebarsDotNet.Pools;
 
@@ -17,6 +18,8 @@ internal static BindingContext Create(ICompiledHandlebarsConfiguration configura
         {
             return Pool.CreateContext(configuration, value, parent, partialBlockTemplate);
         }
+
+        private int _claimed;
 
         public void Dispose() => Pool.Return(this);
 
@@ -39,12 +42,23 @@ public BindingContext CreateContext(ICompiledHandlebarsConfiguration configurati
                 return context;
             }
 
-            internal struct BindingContextPolicy : IInternalObjectPoolPolicy<BindingContext>
+            internal readonly struct BindingContextPolicy : IInternalObjectPoolPolicy<BindingContext>
             {
-                public BindingContext Create() => new BindingContext();
+                public BindingContext Create() => new(claim: true);
+
+                public bool TryClaim(BindingContext item)
+                {
+                    return Interlocked
+                        .CompareExchange(ref item._claimed, 1, 0) == 0;
+                }
 
                 public bool Return(BindingContext item)
                 {
+                    var shouldReturn = Interlocked
+                        .CompareExchange(ref item._claimed, 0, 1) == 1;
+                    
+                    if (!shouldReturn) return false;
+                    
                     item.Root = null;
                     item.Value = null;
                     item.ParentContext = null;

source/Handlebars/Polyfills/AsyncLocal.cs

@@ -36,6 +36,7 @@ public ClosureBuilderPool(Policy policy) : base(policy)
         private readonly struct Policy : IInternalObjectPoolPolicy<ClosureBuilder>
         {
             public ClosureBuilder Create() => new ();
+            public bool TryClaim(ClosureBuilder item) => true;
             public bool Return(ClosureBuilder item) => true;
         }
     }

source/Handlebars/Pools/BindingContext.Pool.cs

@@ -10,6 +10,7 @@ private GenericObjectPool() : base(new Policy()) { }
         public readonly struct Policy : IInternalObjectPoolPolicy<T>
         {
             public T Create() => new ();
+            public bool TryClaim(T item) => true;
             public bool Return(T item) => true;
         }
     }