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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;

using System.Diagnostics;

using Microsoft.Scripting.Runtime;

using Microsoft.Scripting.Utils;

using IronPython.Runtime.Exceptions;

namespace IronPython.Runtime {

/// <summary>

/// Cached global value. Created and maintained on a per-language basis. Default

/// implementation returns a singleton which indicates caching is not occuring.

/// </summary>

public sealed class ModuleGlobalCache {

private object _value;

internal static readonly object NotCaching = new object();

internal static readonly ModuleGlobalCache NoCache = new ModuleGlobalCache(NotCaching);

/// <summary>

/// Creates a new ModuleGlobalCache with the specified value.

/// </summary>

public ModuleGlobalCache(object value) {

_value = value;

}

/// <summary>

/// True if the ModuleGlobalCache is participating in a caching strategy.

/// </summary>

public bool IsCaching {

get {

return _value != NotCaching;

}

}

/// <summary>

/// True if there is currently a value associated with this global variable. False if

/// it is currently unassigned.

/// </summary>

public bool HasValue {

get {

return _value != Uninitialized.Instance;

}

}

/// <summary>

/// Gets or sets the current cached value

/// </summary>

public object Value {

get {

return _value;

}

set {

if (_value == NotCaching) throw new ValueErrorException("Cannot change non-caching value.");

_value = value;

}

}

/// <summary>

/// Event handler for when the value has changed. Language implementors should call this when

/// the cached value is invalidated.

/// </summary>

[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Security", "CA2109:ReviewVisibleEventHandlers")]

public void Changed(object sender, ModuleChangeEventArgs e) {

ContractUtils.RequiresNotNull(e, "e");

switch (e.ChangeType) {

case ModuleChangeType.Delete: Value = Uninitialized.Instance; break;

case ModuleChangeType.Set: Value = e.Value; break;

default: Debug.Assert(false, "unknown ModuleChangeType"); break;

}

}

}

}