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*
* Copyright (c) Microsoft Corporation.
*
* This source code is subject to terms and conditions of the Apache License, Version 2.0. A
* copy of the license can be found in the License.html file at the root of this distribution. If
* you cannot locate the Apache License, Version 2.0, please send an email to
* dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound
* by the terms of the Apache License, Version 2.0.
*
* You must not remove this notice, or any other, from this software.
*
*
* ***************************************************************************/
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Runtime.CompilerServices;
namespace System.Management.Automation.Interpreter
{
/// <summary>
/// A simple forth-style stack machine for executing Expression trees
/// without the need to compile to IL and then invoke the JIT. This trades
/// off much faster compilation time for a slower execution performance.
/// For code that is only run a small number of times this can be a
/// sweet spot.
///
/// The core loop in the interpreter is the RunInstructions method.
/// </summary>
internal sealed class Interpreter
{
internal static readonly object NoValue = new object();
internal const int RethrowOnReturn = Int32.MaxValue;
// zero: sync compilation
// negative: default
internal readonly int _compilationThreshold;
internal readonly object[] _objects;
internal readonly RuntimeLabel[] _labels;
internal readonly string _name;
internal readonly DebugInfo[] _debugInfos;
internal Interpreter(string name, LocalVariables locals, HybridReferenceDictionary<LabelTarget, BranchLabel> labelMapping,
InstructionArray instructions, DebugInfo[] debugInfos, int compilationThreshold)
{
_name = name;
LocalCount = locals.LocalCount;
ClosureVariables = locals.ClosureVariables;
Instructions = instructions;
_objects = instructions.Objects;
_labels = instructions.Labels;
LabelMapping = labelMapping;
_debugInfos = debugInfos;
_compilationThreshold = compilationThreshold;
}
internal int ClosureSize
{
get
{
if (ClosureVariables == null)
{
return 0;
}
return ClosureVariables.Count;
}
}
internal int LocalCount { get; }
internal bool CompileSynchronously
{
get { return _compilationThreshold <= 1; }
}
internal InstructionArray Instructions { get; }
internal Dictionary<ParameterExpression, LocalVariable> ClosureVariables { get; }
internal HybridReferenceDictionary<LabelTarget, BranchLabel> LabelMapping { get; }
/// <summary>
/// Runs instructions within the given frame.
/// </summary>
/// <remarks>
/// Interpreted stack frames are linked via Parent reference so that each CLR frame of this method corresponds
/// to an interpreted stack frame in the chain. It is therefore possible to combine CLR stack traces with
/// interpreted stack traces by aligning interpreted frames to the frames of this method.
/// Each group of subsequent frames of Run method corresponds to a single interpreted frame.
/// </remarks>
[SpecialName, MethodImpl(MethodImplOptions.NoInlining)]
public void Run(InterpretedFrame frame)
{
var instructions = Instructions.Instructions;
int index = frame.InstructionIndex;
while (index < instructions.Length)
{
index += instructions[index].Run(frame);
frame.InstructionIndex = index;
}
}
}
}
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