FileStream.Lock Method

Prevents other processes from changing the FileStream.

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

public virtual void Lock(
	long position,
	long length
)

Parameters

position
Type: System.Int64

The beginning of the range to lock. The value of this parameter must be equal to or greater than zero (0).

length
Type: System.Int64

The range to be locked.

ExceptionCondition
ArgumentOutOfRangeException

position or length is negative.

ObjectDisposedException

The file is closed.

IOException

The process cannot access the file because another process has locked a portion of the file.

Locking a range of a file stream gives the threads of the locking process exclusive access to that range of the file stream.

For a list of common I/O tasks, 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. 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;
                }
            }
        }
    }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

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

.NET Framework

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