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//------------------------------------------------------------------------------
//
// <copyright file="ChannelManager.cs" company="Microsoft">
// Copyright (C) Microsoft Corporation. All rights reserved.
// </copyright>
//
// Description:
// The ChannelManager is a helper structure internal to MediaContext
// that abstracts out channel creation, storage and destruction.
//
//------------------------------------------------------------------------------
using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Threading;
using System.Windows.Threading;
using System.Windows;
using System.Windows.Interop;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Media.Composition;
using System.Security;
using MS.Internal;
using MS.Utility;
using MS.Win32;
using Microsoft.Win32.SafeHandles;
using SR=MS.Internal.PresentationCore.SR;
using SRID=MS.Internal.PresentationCore.SRID;
using UnsafeNativeMethods=MS.Win32.PresentationCore.UnsafeNativeMethods.MilCoreApi;
namespace System.Windows.Media
{
partial class MediaContext
{
/// <summary>
/// A helper structure that abstracts channel management.
/// </summary>
/// <remarks>
/// The common agreement (avcomptm, avpttrev) is that channel creation
/// should be considered unsafe and therefore subject to control via
/// the SecurityCritical/SecurityTreatAsSafe mechanism.
///
/// On the other hand, using a channel that has been created by the
/// MediaContext is considered safe.
///
/// This class expresses the above policy by hiding channel creation
/// and storage within the MediaContext while allowing to access
/// the channels at will.
/// </remarks>
private struct ChannelManager
{
/// <summary>
/// Opens an asynchronous channel.
/// </summary>
/// <securitynote>
/// Critical - Creates a channel, calls a Channel method, calls methods performing elevations.
/// TreatAsSafe - It is safe for the media context to create and use a channel.
/// </securitynote>
[SecurityCritical, SecurityTreatAsSafe]
internal void CreateChannels()
{
Invariant.Assert(_asyncChannel == null);
Invariant.Assert(_asyncOutOfBandChannel == null);
// Create a channel into the async composition device.
// Pass in a reference to the global mediasystem channel so that it uses
// the same partition.
_asyncChannel = new DUCE.Channel(
System.Windows.Media.MediaSystem.ServiceChannel,
false, // not out of band
System.Windows.Media.MediaSystem.Connection,
false // sync transport
);
_asyncOutOfBandChannel = new DUCE.Channel(
System.Windows.Media.MediaSystem.ServiceChannel,
true, // out of band
System.Windows.Media.MediaSystem.Connection,
false // sync transport
);
}
/// <summary>
/// Closes all opened channels.
/// </summary>
/// <securitynote>
/// Critical - Closes channels.
/// TreatAsSafe - It is safe for the media context to sync channels channel.
/// </securitynote>
[SecurityCritical, SecurityTreatAsSafe]
internal void RemoveSyncChannels()
{
//
// Close the synchronous channels.
//
if (_freeSyncChannels != null)
{
while (_freeSyncChannels.Count > 0)
{
_freeSyncChannels.Dequeue().Close();
}
_freeSyncChannels = null;
}
if (_syncServiceChannel != null)
{
_syncServiceChannel.Close();
_syncServiceChannel = null;
}
}
/// <summary>
/// Closes all opened channels.
/// </summary>
/// <securitynote>
/// Critical - Closes channels.
/// TreatAsSafe - It is safe for the media context to close a channel.
/// </securitynote>
[SecurityCritical, SecurityTreatAsSafe]
internal void RemoveChannels()
{
if (_asyncChannel != null)
{
_asyncChannel.Close();
_asyncChannel = null;
}
if (_asyncOutOfBandChannel != null)
{
_asyncOutOfBandChannel.Close();
_asyncOutOfBandChannel = null;
}
RemoveSyncChannels();
if (_pSyncConnection != IntPtr.Zero)
{
HRESULT.Check(UnsafeNativeMethods.WgxConnection_Disconnect(_pSyncConnection));
_pSyncConnection = IntPtr.Zero;
}
}
/// <summary>
/// Create a fresh or fetch one from the pool synchronous channel.
/// </summary>
/// <securitynote>
/// Critical - Calls critical methods to create a synchronous channel and return it.
/// TreatAsSafe - This function allocates the channel in a Channel class that guards channel
/// access from insecure access. It is also ok for this method to allocate the native objects
/// since there is nothing security critical about having the channel infrastructure initialized.
/// </securitynote>
[SecurityCritical, SecurityTreatAsSafe]
internal DUCE.Channel AllocateSyncChannel()
{
DUCE.Channel syncChannel;
if (_pSyncConnection == IntPtr.Zero)
{
HRESULT.Check(UnsafeNativeMethods.WgxConnection_Create(
true, // true means synchronous transport
out _pSyncConnection));
}
if (_freeSyncChannels == null)
{
//
// Ensure the free sync channels queue...
//
_freeSyncChannels = new Queue<DUCE.Channel>(3);
}
if (_freeSyncChannels.Count > 0)
{
//
// If there is a free sync channel in the queue, we're done:
//
return _freeSyncChannels.Dequeue();
}
else
{
//
// Otherwise, create a new channel. We will try to cache it
// when the ReleaseSyncChannel call is made. Also ensure the
// synchronous service channel and glyph cache.
//
if (_syncServiceChannel == null)
{
_syncServiceChannel = new DUCE.Channel(
null,
false, // not out of band
_pSyncConnection,
true // synchronous
);
}
syncChannel = new DUCE.Channel(
_syncServiceChannel,
false, // not out of band
_pSyncConnection,
true // synchronous
);
return syncChannel;
}
}
/// <summary>
/// Returns a sync channel back to the pool.
/// </summary>
/// <securitynote>
/// Critical - Creates and returns a synchronous channel.
/// TreatAsSafe - Closing a channel is safe.
/// </securitynote>
[SecurityCritical, SecurityTreatAsSafe]
internal void ReleaseSyncChannel(DUCE.Channel channel)
{
Invariant.Assert(_freeSyncChannels != null);
//
// A decision needs to be made whether or not we're interested
// in re-using this channel later. For now, store up to three
// synchronous channel in the queue.
//
if (_freeSyncChannels.Count <= 3)
{
_freeSyncChannels.Enqueue(channel);
}
else
{
channel.Close();
}
}
/// <summary>
/// Returns the asynchronous channel.
/// </summary>
/// <SecurityNote>
/// Critical - Channels are a controlled unmanaged resource.
/// TreatAsSafe - Using a channel created by the media context is safe.
/// </SecurityNote>
internal DUCE.Channel Channel
{
[SecurityCritical, SecurityTreatAsSafe]
get
{
return _asyncChannel;
}
}
/// <summary>
/// Returns the asynchronous out-of-band channel.
/// </summary>
/// <SecurityNote>
/// Critical - Channels are a controlled unmanaged resource.
/// TreatAsSafe - Using a channel created by the media context is safe.
/// </SecurityNote>
internal DUCE.Channel OutOfBandChannel
{
[SecurityCritical, SecurityTreatAsSafe]
get
{
return _asyncOutOfBandChannel;
}
}
/// <summary>
/// The asynchronous channel.
/// </summary>
/// <remarks>
/// This field will be replaced with an asynchronous channel table as per task #26681.
/// </remarks>
/// <SecurityNote>
/// Critical - Channels are a controlled unmanaged resource.
/// </SecurityNote>
[SecurityCritical]
private DUCE.Channel _asyncChannel;
/// <summary>
/// The asynchronous out-of-band channel.
/// </summary>
/// <remarks>
/// This is needed by CompositionTarget for handling WM_PAINT, etc.
/// </remarks>
/// <SecurityNote>
/// Critical - Channels are a controlled unmanaged resource.
/// </SecurityNote>
[SecurityCritical]
private DUCE.Channel _asyncOutOfBandChannel;
/// <summary>
/// We store the free synchronous channels for later re-use in this queue.
/// </summary>
/// <SecurityNote>
/// Critical - Channels are a controlled unmanaged resource.
/// </SecurityNote>
[SecurityCritical]
private Queue<DUCE.Channel> _freeSyncChannels;
/// <summary>
/// The service channel to the synchronous partition.
/// </summary>
/// <SecurityNote>
/// Critical - Channels are a controlled unmanaged resource.
/// </SecurityNote>
[SecurityCritical]
private DUCE.Channel _syncServiceChannel;
/// <summary>
/// Pointer to the unmanaged connection object.
/// </summary>
/// <SecurityNote>
/// Critical - Controlled unmanaged resource.
/// </SecurityNote>
[SecurityCritical]
private IntPtr _pSyncConnection;
}
}
}
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