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StreamingContextStates Enumeration

Defines a set of flags that specifies the source or destination context for the stream during serialization.

This enumeration has a FlagsAttribute attribute that allows a bitwise combination of its member values.

Namespace:  System.Runtime.Serialization
Assembly:  mscorlib (in mscorlib.dll)

[SerializableAttribute]
[ComVisibleAttribute(true)]
[FlagsAttribute]
public enum StreamingContextStates

Member nameDescription
CrossProcessSpecifies that the source or destination context is a different process on the same computer.
CrossMachineSpecifies that the source or destination context is a different computer.
FileSpecifies that the source or destination context is a file. Users can assume that files will last longer than the process that created them and not serialize objects in such a way that deserialization will require accessing any data from the current process.
PersistenceSpecifies that the source or destination context is a persisted store, which could include databases, files, or other backing stores. Users can assume that persisted data will last longer than the process that created the data and not serialize objects so that deserialization will require accessing any data from the current process.
RemotingSpecifies that the data is remoted to a context in an unknown location. Users cannot make any assumptions whether this is on the same computer.
OtherSpecifies that the serialization context is unknown.
CloneSpecifies that the object graph is being cloned. Users can assume that the cloned graph will continue to exist within the same process and be safe to access handles or other references to unmanaged resources.
CrossAppDomainSpecifies that the source or destination context is a different AppDomain. (For a description of AppDomains, see [<topic://cpconapplicationdomains>]).
AllSpecifies that the serialized data can be transmitted to or received from any of the other contexts.

The following code example demonstrates the use of the StreamingContextStates enum.


// Note: You must compile this file using the C# /unsafe switch.
using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Formatters.Binary;
using System.Runtime.Serialization;
using System.Runtime.InteropServices;
using System.Security.Permissions;

[assembly: SecurityPermission(
SecurityAction.RequestMinimum, Execution = true)]
// This class includes several Win32 interop definitions.
internal class Win32
{
    public static readonly IntPtr InvalidHandleValue = new IntPtr(-1);
    public const UInt32 FILE_MAP_WRITE = 2;
    public const UInt32 PAGE_READWRITE = 0x04;

    [DllImport("Kernel32",CharSet=CharSet.Unicode)]
    public static extern IntPtr CreateFileMapping(IntPtr hFile,
        IntPtr pAttributes, UInt32 flProtect,
        UInt32 dwMaximumSizeHigh, UInt32 dwMaximumSizeLow, String pName);

    [DllImport("Kernel32",CharSet=CharSet.Unicode)]
    public static extern IntPtr OpenFileMapping(UInt32 dwDesiredAccess,
        Boolean bInheritHandle, String name);

    [DllImport("Kernel32",CharSet=CharSet.Unicode)]
    public static extern Boolean CloseHandle(IntPtr handle);

    [DllImport("Kernel32",CharSet=CharSet.Unicode)]
    public static extern IntPtr MapViewOfFile(IntPtr hFileMappingObject,
        UInt32 dwDesiredAccess,
        UInt32 dwFileOffsetHigh, UInt32 dwFileOffsetLow,
        IntPtr dwNumberOfBytesToMap);

    [DllImport("Kernel32",CharSet=CharSet.Unicode)]
    public static extern Boolean UnmapViewOfFile(IntPtr address);

    [DllImport("Kernel32",CharSet=CharSet.Unicode)]
    public static extern Boolean DuplicateHandle(IntPtr hSourceProcessHandle,
        IntPtr hSourceHandle,
        IntPtr hTargetProcessHandle, ref IntPtr lpTargetHandle,
        UInt32 dwDesiredAccess, Boolean bInheritHandle, UInt32 dwOptions);
    public const UInt32 DUPLICATE_CLOSE_SOURCE = 0x00000001;
    public const UInt32 DUPLICATE_SAME_ACCESS = 0x00000002;

    [DllImport("Kernel32",CharSet=CharSet.Unicode)]
    public static extern IntPtr GetCurrentProcess();
}


// This class wraps memory that can be simultaneously 
// shared by multiple AppDomains and Processes.
[Serializable]
public sealed class SharedMemory : ISerializable, IDisposable
{
    // The handle and string that identify 
    // the Windows file-mapping object.
    private IntPtr m_hFileMap = IntPtr.Zero;
    private String m_name;

    // The address of the memory-mapped file-mapping object.
    private IntPtr m_address;

    public unsafe Byte* Address
    {
        get { return (Byte*)m_address; }
    }

    // The constructors.
    public SharedMemory(Int32 size) : this(size, null) { }

    public SharedMemory(Int32 size, String name)
    {
        m_hFileMap = Win32.CreateFileMapping(Win32.InvalidHandleValue,
            IntPtr.Zero, Win32.PAGE_READWRITE,
            0, unchecked((UInt32)size), name);
        if (m_hFileMap == IntPtr.Zero)
            throw new Exception("Could not create memory-mapped file.");
        m_name = name;
        m_address = Win32.MapViewOfFile(m_hFileMap, Win32.FILE_MAP_WRITE,
            0, 0, IntPtr.Zero);
    }

    // The cleanup methods.
    public void Dispose()
    {
        GC.SuppressFinalize(this);
        Dispose(true);
    }

    private void Dispose(Boolean disposing)
    {
        Win32.UnmapViewOfFile(m_address);
        Win32.CloseHandle(m_hFileMap);
        m_address = IntPtr.Zero;
        m_hFileMap = IntPtr.Zero;
    }

    ~SharedMemory()
    {
        Dispose(false);
    }

    // Private helper methods.
    private static Boolean AllFlagsSet(Int32 flags, Int32 flagsToTest)
    {
        return (flags & flagsToTest) == flagsToTest;
    }

    private static Boolean AnyFlagsSet(Int32 flags, Int32 flagsToTest)
    {
        return (flags & flagsToTest) != 0;
    }


    // The security attribute demands that code that calls  
    // this method have permission to perform serialization.
    [SecurityPermissionAttribute(SecurityAction.Demand, SerializationFormatter = true)]
    void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context)
    {
        // The context's State member indicates
        // where the object will be deserialized.

        // A SharedMemory object cannot be serialized 
        // to any of the following destinations.
        const StreamingContextStates InvalidDestinations =
                  StreamingContextStates.CrossMachine |
                  StreamingContextStates.File |
                  StreamingContextStates.Other |
                  StreamingContextStates.Persistence |
                  StreamingContextStates.Remoting;
        if (AnyFlagsSet((Int32)context.State, (Int32)InvalidDestinations))
            throw new SerializationException("The SharedMemory object " +
                "cannot be serialized to any of the following streaming contexts: " +
                InvalidDestinations);

        const StreamingContextStates DeserializableByHandle =
                  StreamingContextStates.Clone |
            // The same process.
                  StreamingContextStates.CrossAppDomain;
        if (AnyFlagsSet((Int32)context.State, (Int32)DeserializableByHandle))
            info.AddValue("hFileMap", m_hFileMap);

        const StreamingContextStates DeserializableByName =
            // The same computer.
                  StreamingContextStates.CrossProcess;
        if (AnyFlagsSet((Int32)context.State, (Int32)DeserializableByName))
        {
            if (m_name == null)
                throw new SerializationException("The SharedMemory object " +
                    "cannot be serialized CrossProcess because it was not constructed " +
                    "with a String name.");
            info.AddValue("name", m_name);
        }
    }


    // The security attribute demands that code that calls  
    // this method have permission to perform serialization.
    [SecurityPermissionAttribute(SecurityAction.Demand, SerializationFormatter = true)]
    private SharedMemory(SerializationInfo info, StreamingContext context)
    {
        // The context's State member indicates 
        // where the object was serialized from.

        const StreamingContextStates InvalidSources =
                  StreamingContextStates.CrossMachine |
                  StreamingContextStates.File |
                  StreamingContextStates.Other |
                  StreamingContextStates.Persistence |
                  StreamingContextStates.Remoting;
        if (AnyFlagsSet((Int32)context.State, (Int32)InvalidSources))
            throw new SerializationException("The SharedMemory object " +
                "cannot be deserialized from any of the following stream contexts: " +
                InvalidSources);

        const StreamingContextStates SerializedByHandle =
                  StreamingContextStates.Clone |
            // The same process.
                  StreamingContextStates.CrossAppDomain;
        if (AnyFlagsSet((Int32)context.State, (Int32)SerializedByHandle))
        {
            try
            {
                Win32.DuplicateHandle(Win32.GetCurrentProcess(),
                    (IntPtr)info.GetValue("hFileMap", typeof(IntPtr)),
                    Win32.GetCurrentProcess(), ref m_hFileMap, 0, false,
                    Win32.DUPLICATE_SAME_ACCESS);
            }
            catch (SerializationException)
            {
                throw new SerializationException("A SharedMemory was not serialized " +
                    "using any of the following streaming contexts: " +
                    SerializedByHandle);
            }
        }

        const StreamingContextStates SerializedByName =
            // The same computer.
                  StreamingContextStates.CrossProcess;
        if (AnyFlagsSet((Int32)context.State, (Int32)SerializedByName))
        {
            try
            {
                m_name = info.GetString("name");
            }
            catch (SerializationException)
            {
                throw new SerializationException("A SharedMemory object was not " +
                    "serialized using any of the following streaming contexts: " +
                    SerializedByName);
            }
            m_hFileMap = Win32.OpenFileMapping(Win32.FILE_MAP_WRITE, false, m_name);
        }
        if (m_hFileMap != IntPtr.Zero)
        {
            m_address = Win32.MapViewOfFile(m_hFileMap, Win32.FILE_MAP_WRITE,
                0, 0, IntPtr.Zero);
        }
        else
        {
            throw new SerializationException("A SharedMemory object could not " +
                "be deserialized.");
        }
    }
}


class App
{
    [STAThread]
    static void Main(string[] args)
    {
        Serialize();
        Console.WriteLine();
        Deserialize();
    }

    unsafe static void Serialize()
    {
        // Create a hashtable of values that will eventually be serialized.
        SharedMemory sm = new SharedMemory(1024, "JeffMemory");
        for (Int32 x = 0; x < 100; x++)
            *(sm.Address + x) = (Byte)x;

        Byte[] b = new Byte[10];
        for (Int32 x = 0; x < b.Length; x++) b[x] = *(sm.Address + x);
        Console.WriteLine(BitConverter.ToString(b));

        // To serialize the SharedMemory object, 
        // you must first open a stream for writing. 
        // Use a file stream here.
        FileStream fs = new FileStream("DataFile.dat", FileMode.Create);

        // Construct a BinaryFormatter and tell it where 
        // the objects will be serialized to.
        BinaryFormatter formatter = new BinaryFormatter(null,
            new StreamingContext(StreamingContextStates.CrossAppDomain));
        try
        {
            formatter.Serialize(fs, sm);
        }
        catch (SerializationException e)
        {
            Console.WriteLine("Failed to serialize. Reason: " + e.Message);
            throw;
        }
        finally
        {
            fs.Close();
        }
    }


    unsafe static void Deserialize()
    {
        // Declare a SharedMemory reference.
        SharedMemory sm = null;

        // Open the file containing the data that you want to deserialize.
        FileStream fs = new FileStream("DataFile.dat", FileMode.Open);
        try
        {
            BinaryFormatter formatter = new BinaryFormatter(null,
                new StreamingContext(StreamingContextStates.CrossAppDomain));

            // Deserialize the SharedMemory object from the file and 
            // assign the reference to the local variable.
            sm = (SharedMemory)formatter.Deserialize(fs);
        }
        catch (SerializationException e)
        {
            Console.WriteLine("Failed to deserialize. Reason: " + e.Message);
            throw;
        }
        finally
        {
            fs.Close();
        }

        // To prove that the SharedMemory object deserialized correctly, 
        // display some of its bytes to the console.
        Byte[] b = new Byte[10];
        for (Int32 x = 0; x < b.Length; x++) b[x] = *(sm.Address + x);
        Console.WriteLine(BitConverter.ToString(b));
    }
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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