FileStream.Lock(Int64, Int64) Método
Definição
Importante
Algumas informações dizem respeito a um produto pré-lançado que pode ser substancialmente modificado antes de ser lançado. A Microsoft não faz garantias, de forma expressa ou implícita, em relação à informação aqui apresentada.
Impede que outros processos leiam ou escrevam no FileStream.
public:
virtual void Lock(long position, long length);public virtual void Lock(long position, long length);abstract member Lock : int64 * int64 -> unit
override this.Lock : int64 * int64 -> unitPublic Overridable Sub Lock (position As Long, length As Long)Parâmetros
- position
- Int64
O início do intervalo para bloquear. O valor deste parâmetro deve ser igual ou maior que zero (0).
- length
- Int64
O campo de tiro deve ser bloqueado.
Exceções
position ou length é negativo.
O processo está encerrado.
O processo não consegue aceder ao ficheiro porque outro processo bloqueou uma parte do ficheiro.
Exemplos
O exemplo de código seguinte demonstra como bloquear parte de um ficheiro para que outro processo não possa aceder a essa parte, mesmo tendo acesso de leitura/escrita ao ficheiro. Executa o programa simultaneamente em diferentes janelas de comandos e investiga usando as diferentes opções de entrada da consola.
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;
}
}
}
}
}
open System
open System.IO
open System.Text
let uniEncoding = UnicodeEncoding()
let lastRecordText = "The last processed record number was: "
let textLength = uniEncoding.GetByteCount lastRecordText
let mutable recordNumber = 13
let byteCount = string recordNumber |> uniEncoding.GetByteCount
do
use fileStream =
new FileStream("Test#@@#.dat", FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite)
// Write the original file data.
if fileStream.Length = 0 then
let tempString = lastRecordText + string recordNumber
fileStream.Write(uniEncoding.GetBytes tempString, 0, uniEncoding.GetByteCount tempString)
// Allow the user to choose the operation.
let mutable consoleInput = 'R'
let readText = int fileStream.Length |> Array.zeroCreate
while consoleInput <> 'X' do
printf "\nEnter 'R' to read, 'W' to write, 'L' to lock, 'U' to unlock, anything else to exit: "
let mutable tempString = stdin.ReadLine()
if tempString.Length = 0 then
consoleInput <- 'X'
else
consoleInput <- Char.ToUpper tempString[0]
match consoleInput with
| 'R' ->
// Read data from the file and
// write it to the console.
try
fileStream.Seek(0, SeekOrigin.Begin) |> ignore
fileStream.Read(readText, 0, int fileStream.Length) |> ignore
tempString <- String(uniEncoding.GetChars readText, 0, readText.Length)
printfn $"{tempString}"
recordNumber <- tempString.IndexOf ':' + 2 |> tempString.Substring |> Int32.Parse
// Catch the IOException generated if the
// specified part of the file is locked.
with :? IOException as e ->
printfn
$"{e.GetType().Name}: The read operation could not be performed because the specified part of the file is locked."
| 'W' ->
// Update the file.
try
fileStream.Seek(textLength, SeekOrigin.Begin) |> ignore
fileStream.Read(readText, textLength - 1, byteCount) |> ignore
tempString <- String(uniEncoding.GetChars readText, textLength - 1, byteCount)
recordNumber <- Int32.Parse tempString + 1
fileStream.Seek(textLength, SeekOrigin.Begin) |> ignore
fileStream.Write(string recordNumber |> uniEncoding.GetBytes, 0, byteCount)
fileStream.Flush()
printfn "Record has been updated."
// Catch the IOException generated if the
// specified part of the file is locked.
with :? IOException as e ->
printfn
$"{e.GetType().Name}: The write operation could not be performed because the specified part of the file is locked."
// Lock the specified part of the file.
| 'L' ->
try
fileStream.Lock(textLength - 1 |> int64, byteCount)
printfn "The specified part of file has been locked."
with :? IOException as e ->
printfn $"{e.GetType().Name}: The specified part of file is already locked."
// Unlock the specified part of the file.
| 'U' ->
try
fileStream.Unlock(textLength - 1 |> int64, byteCount)
printfn "The specified part of file has been unlocked."
with :? IOException as e ->
printfn $"{e.GetType().Name}: The specified part of file is not locked by the current process."
// Exit the program.
| _ -> consoleInput <- 'X'
Imports System.IO
Imports System.Text
Public Class FStreamLock
Shared Sub Main()
Dim uniEncoding As New UnicodeEncoding()
Dim lastRecordText As String = _
"The last processed record number was: "
Dim textLength As Integer = _
uniEncoding.GetByteCount(lastRecordText)
Dim recordNumber As Integer = 13
Dim byteCount As Integer = _
uniEncoding.GetByteCount(recordNumber.ToString())
Dim tempString As String
Dim aFileStream As New FileStream( _
"Test#@@#.dat", FileMode.OpenOrCreate, _
FileAccess.ReadWrite, FileShare.ReadWrite)
Try
' Write the original file data.
If aFileStream.Length = 0 Then
tempString = _
lastRecordText + recordNumber.ToString()
aFileStream.Write(uniEncoding.GetBytes(tempString), _
0, uniEncoding.GetByteCount(tempString))
End If
' Allow the user to choose the operation.
Dim consoleInput As Char = "R"C
Dim readText(CInt(aFileStream.Length)) As Byte
While consoleInput <> "X"C
Console.Write(vbcrLf & _
"Enter 'R' to read, 'W' to write, 'L' to " & _
"lock, 'U' to unlock, anything else to exit: ")
tempString = Console.ReadLine()
If tempString.Length = 0 Then
Exit While
End If
consoleInput = Char.ToUpper(tempString.Chars(0))
Select consoleInput
' Read data from the file and
' write it to the console.
Case "R"C
Try
aFileStream.Seek(0, SeekOrigin.Begin)
aFileStream.Read( _
readText, 0, CInt(aFileStream.Length))
tempString = New String( _
uniEncoding.GetChars( _
readText, 0, readText.Length))
Console.WriteLine(tempString)
recordNumber = Integer.Parse( _
tempString.Substring( _
tempString.IndexOf(":"C) + 2))
' Catch the IOException generated if the
' specified part of the file is locked.
Catch ex As IOException
Console.WriteLine("{0}: The read " & _
"operation could not be performed " & _
"because the specified part of the" & _
" file is locked.", _
ex.GetType().Name)
End Try
Exit Select
' Update the file.
Case "W"C
Try
aFileStream.Seek(textLength, _
SeekOrigin.Begin)
aFileStream.Read( _
readText, textLength - 1, byteCount)
tempString = New String( _
uniEncoding.GetChars( _
readText, textLength - 1, byteCount))
recordNumber = _
Integer.Parse(tempString) + 1
aFileStream.Seek( _
textLength, SeekOrigin.Begin)
aFileStream.Write(uniEncoding.GetBytes( _
recordNumber.ToString()), 0, byteCount)
aFileStream.Flush()
Console.WriteLine( _
"Record has been updated.")
' Catch the IOException generated if the
' specified part of the file is locked.
Catch ex As IOException
Console.WriteLine( _
"{0}: The write operation could " & _
"not be performed because the " & _
"specified part of the file is " & _
"locked.", ex.GetType().Name)
End Try
Exit Select
' Lock the specified part of the file.
Case "L"C
Try
aFileStream.Lock(textLength - 1, byteCount)
Console.WriteLine("The specified part " & _
"of file has been locked.")
Catch ex As IOException
Console.WriteLine( _
"{0}: The specified part of file " & _
"is already locked.", _
ex.GetType().Name)
End Try
Exit Select
' Unlock the specified part of the file.
Case "U"C
Try
aFileStream.Unlock( _
textLength - 1, byteCount)
Console.WriteLine("The specified part " & _
"of file has been unlocked.")
Catch ex As IOException
Console.WriteLine( _
"{0}: The specified part of file " & _
"is not locked by the current " & _
"process.", ex.GetType().Name)
End Try
Exit Select
' Exit the program.
Case Else
consoleInput = "X"C
Exit While
End Select
End While
Finally
aFileStream.Close()
End Try
End Sub
End Class
Observações
Bloquear um intervalo de um fluxo de ficheiros dá aos threads do processo de bloqueio acesso exclusivo a esse intervalo do fluxo de ficheiros.
Para obter uma lista de operações comuns de arquivos e diretórios, consulte Tarefas comuns de E/S.