MegaBites-AI/Windows-powershell

1/* ****************************************************************************2 *3 * Copyright (c) Microsoft Corporation.4 *5 * This source code is subject to terms and conditions of the Apache License, Version 2.0. A6 * copy of the license can be found in the License.html file at the root of this distribution. If7 * you cannot locate the Apache License, Version 2.0, please send an email to8 * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound9 * by the terms of the Apache License, Version 2.0.10 *11 * You must not remove this notice, or any other, from this software.12 *13 *14 * ***************************************************************************/15 16using System.Collections.Generic;17using System.Linq.Expressions;18using System.Runtime.CompilerServices;19 20namespace System.Management.Automation.Interpreter21{22    /// <summary>23    /// A simple forth-style stack machine for executing Expression trees24    /// without the need to compile to IL and then invoke the JIT.  This trades25    /// off much faster compilation time for a slower execution performance.26    /// For code that is only run a small number of times this can be a27    /// sweet spot.28    ///29    /// The core loop in the interpreter is the RunInstructions method.30    /// </summary>31    internal sealed class Interpreter32    {33        internal static readonly object NoValue = new object();34 35        internal const int RethrowOnReturn = Int32.MaxValue;36 37        // zero: sync compilation38        // negative: default39        internal readonly int _compilationThreshold;40 41        internal readonly object[] _objects;42        internal readonly RuntimeLabel[] _labels;43 44        internal readonly string _name;45        internal readonly DebugInfo[] _debugInfos;46 47        internal Interpreter(string name, LocalVariables locals, HybridReferenceDictionary<LabelTarget, BranchLabel> labelMapping,48            InstructionArray instructions, DebugInfo[] debugInfos, int compilationThreshold)49        {50            _name = name;51            LocalCount = locals.LocalCount;52            ClosureVariables = locals.ClosureVariables;53 54            Instructions = instructions;55            _objects = instructions.Objects;56            _labels = instructions.Labels;57            LabelMapping = labelMapping;58 59            _debugInfos = debugInfos;60            _compilationThreshold = compilationThreshold;61        }62 63        internal int ClosureSize64        {65            get66            {67                if (ClosureVariables == null)68                {69                    return 0;70                }71 72                return ClosureVariables.Count;73            }74        }75 76        internal int LocalCount { get; }77 78        internal bool CompileSynchronously79        {80            get { return _compilationThreshold <= 1; }81        }82 83        internal InstructionArray Instructions { get; }84 85        internal Dictionary<ParameterExpression, LocalVariable> ClosureVariables { get; }86 87        internal HybridReferenceDictionary<LabelTarget, BranchLabel> LabelMapping { get; }88 89        /// <summary>90        /// Runs instructions within the given frame.91        /// </summary>92        /// <remarks>93        /// Interpreted stack frames are linked via Parent reference so that each CLR frame of this method corresponds94        /// to an interpreted stack frame in the chain. It is therefore possible to combine CLR stack traces with95        /// interpreted stack traces by aligning interpreted frames to the frames of this method.96        /// Each group of subsequent frames of Run method corresponds to a single interpreted frame.97        /// </remarks>98        [SpecialName, MethodImpl(MethodImplOptions.NoInlining)]99        public void Run(InterpretedFrame frame)100        {101            var instructions = Instructions.Instructions;102            int index = frame.InstructionIndex;103            while (index < instructions.Length)104            {105                index += instructions[index].Run(frame);106                frame.InstructionIndex = index;107            }108        }109    }110}111