FileStream::Unlock Method (Int64, Int64)

 

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 long position,
	long long length
)

Parameters

position
Type: System::Int64

The beginning of the range to unlock.

length
Type: System::Int64

The range to be unlocked.

Exception Condition
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 namespace System;
using namespace System::IO;
using namespace System::Text;
int main()
{
   UnicodeEncoding^ uniEncoding = gcnew 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;

   FileStream^ fileStream = gcnew FileStream( "Test#@@#.dat",FileMode::OpenOrCreate,FileAccess::ReadWrite,FileShare::ReadWrite );

   try
   {

      // Write the original file data.
      if ( fileStream->Length == 0 )
      {
         tempString = String::Concat( lastRecordText, recordNumber.ToString() );
         fileStream->Write( uniEncoding->GetBytes( tempString ), 0, uniEncoding->GetByteCount( tempString ) );
      }

      // Allow the user to choose the operation.
      Char consoleInput = 'R';
      array<Byte>^readText = gcnew array<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 )
         {
            case 'R':
               try
               {
                  fileStream->Seek( 0, SeekOrigin::Begin );
                  fileStream->Read( readText, 0, (int)fileStream->Length );
                  tempString = gcnew 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()->Name );
               }

               break;

            // Update the file.
            case 'W':
               try
               {
                  fileStream->Seek( textLength, SeekOrigin::Begin );
                  fileStream->Read( readText, textLength - 1, byteCount );
                  tempString = gcnew String( uniEncoding->GetChars( readText, textLength - 1, byteCount ) );
                  recordNumber = Int32::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;

            default:

               // Exit the program.
               consoleInput = 'X';
               break;
         }
      }
   }
   finally
   {
      fileStream->Close();
   }

}

.NET Framework
Available since 1.1
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