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FileStream.Unlock Method

Allows access by other processes to all or part of a file that was previously locked.

Namespace:  System.IO
Assembly:  mscorlib (in mscorlib.dll)

public virtual void Unlock(
	long position,
	long length
)

Parameters

position
Type: System.Int64

The beginning of the range to unlock.

length
Type: System.Int64

The range to be unlocked.

ExceptionCondition
ArgumentOutOfRangeException

position or length is negative.

For a list of common file and directory operations, see Common I/O Tasks.

The following code example demonstrates how to lock part of a file so another process cannot access that part of the file even though it has read/write access to the file, and then unlock the specified part of the file . Run the program simultaneously in different command windows and investigate using the different console input options.

using System;
using System.IO;
using System.Text;

class FStreamLock
{
    static void Main()
    {
        UnicodeEncoding uniEncoding = new UnicodeEncoding();
        string lastRecordText = 
            "The last processed record number was: ";
        int textLength = uniEncoding.GetByteCount(lastRecordText);
        int recordNumber = 13;
        int byteCount = 
            uniEncoding.GetByteCount(recordNumber.ToString());
        string tempString;

        using(FileStream fileStream = new FileStream(
            "Test#@@#.dat", FileMode.OpenOrCreate, 
            FileAccess.ReadWrite, FileShare.ReadWrite))
        {
            // Write the original file data. 
            if(fileStream.Length == 0)
            {
                tempString = 
                    lastRecordText + recordNumber.ToString();
                fileStream.Write(uniEncoding.GetBytes(tempString), 
                    0, uniEncoding.GetByteCount(tempString));
            }

            // Allow the user to choose the operation. 
            char consoleInput = 'R';
            byte[] readText = new byte[fileStream.Length];
            while(consoleInput != 'X')
            {
                Console.Write(
                    "\nEnter 'R' to read, 'W' to write, 'L' to " + 
                    "lock, 'U' to unlock, anything else to exit: ");

                if((tempString = Console.ReadLine()).Length == 0)
                {
                    break;
                }
                consoleInput = char.ToUpper(tempString[0]);
                switch(consoleInput)
                {
                    // Read data from the file and  
                    // write it to the console. 
                    case 'R':
                        try
                        {
                            fileStream.Seek(0, SeekOrigin.Begin);
                            fileStream.Read(
                                readText, 0, (int)fileStream.Length);
                            tempString = new String(
                                uniEncoding.GetChars(
                                readText, 0, readText.Length));
                            Console.WriteLine(tempString);
                            recordNumber = int.Parse(
                                tempString.Substring(
                                tempString.IndexOf(':') + 2));
                        }

                        // Catch the IOException generated if the  
                        // specified part of the file is locked. 
                        catch(IOException e)
                        {
                            Console.WriteLine("{0}: The read " +
                                "operation could not be performed " +
                                "because the specified part of the " +
                                "file is locked.", 
                                e.GetType().Name);
                        }
                        break;

                    // Update the file. 
                    case 'W':
                        try
                        {
                            fileStream.Seek(textLength, 
                                SeekOrigin.Begin);
                            fileStream.Read(
                                readText, textLength - 1, byteCount);
                            tempString = new String(
                                uniEncoding.GetChars(
                                readText, textLength - 1, byteCount));
                            recordNumber = int.Parse(tempString) + 1;
                            fileStream.Seek(
                                textLength, SeekOrigin.Begin);
                            fileStream.Write(uniEncoding.GetBytes(
                                recordNumber.ToString()), 
                                0, byteCount);
                            fileStream.Flush();
                            Console.WriteLine(
                                "Record has been updated.");
                        }

                        // Catch the IOException generated if the  
                        // specified part of the file is locked. 
                        catch(IOException e)
                        {
                            Console.WriteLine(
                                "{0}: The write operation could not " +
                                "be performed because the specified " +
                                "part of the file is locked.", 
                                e.GetType().Name);
                        }
                        break;

                    // Lock the specified part of the file. 
                    case 'L':
                        try
                        {
                            fileStream.Lock(textLength - 1, byteCount);
                            Console.WriteLine("The specified part " +
                                "of file has been locked.");
                        }
                        catch(IOException e)
                        {
                            Console.WriteLine(
                                "{0}: The specified part of file is" +
                                " already locked.", e.GetType().Name);
                        }
                        break;

                    // Unlock the specified part of the file. 
                    case 'U':
                        try
                        {
                            fileStream.Unlock(
                                textLength - 1, byteCount);
                            Console.WriteLine("The specified part " +
                                "of file has been unlocked.");
                        }
                        catch(IOException e)
                        {
                            Console.WriteLine(
                                "{0}: The specified part of file is " +
                                "not locked by the current process.", 
                                e.GetType().Name);
                        }
                        break;

                    // Exit the program. 
                    default:
                        consoleInput = 'X';
                        break;
                }
            }
        }
    }
}

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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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