Field resolvers are mutable

Sources/GraphQL/Type/Definition.swift

@@ -276,8 +276,8 @@ public final class GraphQLObjectType: @unchecked Sendable {
     public let name: String
     public let description: String?
 
-    // While technically not sendable, fields and interfaces should not be mutated after schema
-    // creation.
+    /// The fields that the object defines. These may be mutated during setup, but should not be
+    /// modified once the schema is being used for execution.
     public var fields: () throws -> GraphQLFieldMap {
         get {
             fieldFunc
@@ -294,6 +294,8 @@ public final class GraphQLObjectType: @unchecked Sendable {
     private var fieldFunc: () throws -> GraphQLFieldMap
     private var fieldCache: GraphQLFieldDefinitionMap?
 
+    /// The interfaces that the object conforms to. These may be mutated during setup, but should
+    /// not be modified once the schema is being used for execution.
     public var interfaces: () throws -> [GraphQLInterfaceType] {
         get {
             interfaceFunc
@@ -505,13 +507,34 @@ public struct GraphQLResolveInfo: Sendable {
 
 public typealias GraphQLFieldMap = OrderedDictionary<String, GraphQLField>
 
-public struct GraphQLField: Sendable {
+public final class GraphQLField: @unchecked Sendable {
     public let type: GraphQLOutputType
     public let args: GraphQLArgumentConfigMap
     public let deprecationReason: String?
     public let description: String?
-    public let resolve: GraphQLFieldResolve?
-    public let subscribe: GraphQLFieldResolve?
+
+    public var resolve: GraphQLFieldResolve? {
+        get {
+            fieldPropertyQueue.sync { _resolve }
+        }
+        set {
+            fieldPropertyQueue.sync(flags: .barrier) { _resolve = newValue }
+        }
+    }
+
+    private var _resolve: GraphQLFieldResolve?
+
+    public var subscribe: GraphQLFieldResolve? {
+        get {
+            fieldPropertyQueue.sync { _subscribe }
+        }
+        set {
+            fieldPropertyQueue.sync(flags: .barrier) { _subscribe = newValue }
+        }
+    }
+
+    private var _subscribe: GraphQLFieldResolve?
+
     public let astNode: FieldDefinition?
 
     public init(
@@ -526,8 +549,8 @@ public struct GraphQLField: Sendable {
         self.deprecationReason = deprecationReason
         self.description = description
         self.astNode = astNode
-        resolve = nil
-        subscribe = nil
+        _resolve = nil
+        _subscribe = nil
     }
 
     public init(
@@ -544,8 +567,8 @@ public struct GraphQLField: Sendable {
         self.deprecationReason = deprecationReason
         self.description = description
         self.astNode = astNode
-        self.resolve = resolve
-        self.subscribe = subscribe
+        _resolve = resolve
+        _subscribe = subscribe
     }
 
     public init(
@@ -562,11 +585,11 @@ public struct GraphQLField: Sendable {
         self.description = description
         self.astNode = astNode
 
-        self.resolve = { source, args, context, info in
+        _resolve = { source, args, context, info in
             let result = try resolve(source, args, context, info)
             return result
         }
-        subscribe = nil
+        _subscribe = nil
     }
 }
 
@@ -711,8 +734,8 @@ public final class GraphQLInterfaceType: @unchecked Sendable {
     public let description: String?
     public let resolveType: GraphQLTypeResolve?
 
-    // While technically not sendable, fields and interfaces should not be mutated after schema
-    // creation.
+    /// The fields that the interface defines. These may be mutated during setup, but should not be
+    /// modified once the schema is being used for execution.
     public var fields: () throws -> GraphQLFieldMap {
         get {
             fieldFunc
@@ -729,6 +752,8 @@ public final class GraphQLInterfaceType: @unchecked Sendable {
     private var fieldFunc: () throws -> GraphQLFieldMap
     private var fieldCache: GraphQLFieldDefinitionMap?
 
+    /// The interfaces that the interface conforms to. This may be mutated during setup, but should
+    /// not be modified once the schema is being used for execution.
     public var interfaces: () throws -> [GraphQLInterfaceType] {
         get {
             interfaceFunc
@@ -869,7 +894,9 @@ public final class GraphQLUnionType: @unchecked Sendable {
     public let name: String
     public let description: String?
     public let resolveType: GraphQLTypeResolve?
-    // While technically not sendable, types should not be mutated after schema creation.
+
+    /// The types that belong to the union. This may be mutated during setup, but must not be
+    /// modified once the schema is being used for execution.
     public internal(set) var types: () throws -> [GraphQLObjectType]
     public let possibleTypeNames: [String: Bool]
     let extensions: [GraphQLUnionTypeExtensions]
@@ -1164,7 +1191,9 @@ public struct GraphQLEnumValueDefinition: Sendable {
 public final class GraphQLInputObjectType: @unchecked Sendable {
     public let name: String
     public let description: String?
-    // While technically not sendable, this should not be mutated after schema creation.
+
+    /// The fields that the input has. This may be mutated during setup, but must not be modified
+    /// once the schema is being used for execution.
     public var fields: () throws -> InputObjectFieldMap
     public let astNode: InputObjectTypeDefinition?
     public let extensionASTNodes: [InputObjectExtensionDefinition]
@@ -1422,3 +1451,10 @@ private let cacheQueue = DispatchQueue(
     label: "graphql.objecttype.cache",
     attributes: .concurrent
 )
+
+/// Shared queue for field property access
+/// Uses reader/writer pattern for read-heavy workload
+private let fieldPropertyQueue = DispatchQueue(
+    label: "graphql.field.properties",
+    attributes: .concurrent
+)