FileStream.Lock Method
.NET Framework 2.0
Prevents other processes from changing the FileStream while permitting read access.
Namespace: System.IO
Assembly: mscorlib (in mscorlib.dll)
Assembly: mscorlib (in mscorlib.dll)
The following table lists examples of other typical or related I/O tasks.
| To do this... | See the example in this topic... |
|---|---|
| Create a text file. | |
| Write to a text file. | |
| Read from a text file. | |
| Append text to a file. | |
| Rename or move a file. | |
| Copy a file. | |
| Get the size of a directory. | |
| Get the attributes of a file. | |
| Set the attributes of a file. | |
| Create a subdirectory. | |
| Read from a binary file. | |
| Write to a binary file. | |
| See the files in a directory. | |
| Sort files in a directory by size. |
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; } } } } }
import System.*;
import System.IO.*;
import System.Text.*;
class FStreamLock
{
public static void main(String[] args)
{
UnicodeEncoding uniEncoding = new UnicodeEncoding();
String lastRecordText = "The last processed record number was: ";
int textLength = uniEncoding.GetByteCount(lastRecordText);
int recordNumber = 13;
int byteCount = uniEncoding.GetByteCount(
(new Integer(recordNumber)).ToString());
String tempString;
FileStream fileStream = new FileStream
("Test#@@#.dat", FileMode.OpenOrCreate, FileAccess.ReadWrite,
FileShare.ReadWrite);
try {
// Write the original file data.
if ( fileStream.get_Length() == 0 ) {
tempString = lastRecordText +(
new Integer( recordNumber)).ToString();
fileStream.Write(uniEncoding.GetBytes(tempString),
0, uniEncoding.GetByteCount(tempString));
}
// Allow the user to choose the operation.
char consoleInput = 'R';
ubyte readText[] = new ubyte[(int) fileStream.get_Length() ];
while((consoleInput != 'X')) {
Console.Write(("\nEnter 'R' to read,'W' to write, 'L' to "
+ "lock, 'U' to unlock, anything else to exit: "));
if (((String)(tempString =
Console.ReadLine())).get_Length() == 0) {
break ;
}
consoleInput = Char.ToUpper( tempString.get_Chars(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.get_Length()));
tempString = new String(
uniEncoding.GetChars(readText,
0, readText.length ));
Console.WriteLine(tempString);
recordNumber = Int32.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().get_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 = Int32.Parse(tempString)+1;
fileStream.Seek(textLength, SeekOrigin.Begin);
fileStream.Write(uniEncoding.GetBytes(
(new Integer( 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().get_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().get_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().get_Name());
}
break;
// Exit the program.
default :
// Exit the program.
consoleInput = 'X';
break;
}
}
}
finally {
fileStream.Dispose();
}
} //main
} //FStreamLock
Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.
