E/S de archivos asincrónica
La E/S sincrónica quiere decir que el método está bloqueado hasta que termina la operación de E/S y, a continuación, el método devuelve sus datos. Con E/S asincrónica, un usuario puede llamar a BeginRead. El subproceso principal puede continuar realizando otro trabajo y, posteriormente, el usuario podrá procesar los datos. Además, puede haber varias solicitudes de E/S pendientes simultáneamente.
Para que se le informe cuando estén disponibles estos datos, puede llamar a EndRead o a EndWrite que se pasan en el IAsyncResult correspondiente a la solicitud de E/S emitida. También se puede proporcionar un método de devolución de llamada que debe llamar a EndRead o a EndWrite para averiguar cuántos bytes se han leído o escrito. La E/S asincrónica puede ofrecer mejor rendimiento si hay muchas solicitudes de E/S pendientes a la vez, pero normalmente requiere una reestructuración a fondo de la aplicación para funcionar correctamente.
La clase Stream admite la combinación de lecturas y escrituras sincrónicas y asincrónicas en la misma secuencia, independientemente de si el sistema operativo lo permite. Stream proporciona implementaciones predeterminadas de operaciones de lectura y escritura asincrónicas por lo que respecta a sus implementaciones sincrónicas y proporciona las implementaciones predeterminadas de operaciones de lectura y escritura sincrónicas respecto a sus implementaciones asincrónicas.
Al implementar una clase derivada de Stream, es necesario proporcionar una implementación de la versión sincrónica o asincrónica de los métodos Read y Write. Aunque está permitido reemplazar Read y Write, y las implementaciones predeterminadas de los métodos asincrónicos (BeginRead, EndRead, BeginWrite y EndWrite) funcionarán correctamente con la implementación de los métodos sincrónicos, esta operación no proporcionará el rendimiento más eficaz. De igual forma, los métodos sincrónicos Read y Write funcionan correctamente si se proporciona una implementación de los métodos asincrónicos, pero normalmente el rendimiento es mejor si se implementan los métodos sincrónicos. Las implementaciones predeterminadas de ReadByte y WriteByte llaman a los métodos Read y Write sincrónicos con una matriz de bytes de un elemento. Al derivar clases de Stream, si se dispone de un búfer de bytes interno, se recomienda especialmente reemplazar estos métodos de acceso al búfer interno y obtener así una mejora en el rendimiento.
Una secuencia que se conecta a un almacén de respaldo reemplaza los métodos sincrónicos o asincrónicos Read y Write para obtener la funcionalidad del otro de forma predeterminada. Si una secuencia no admite las operaciones sincrónicas o asincrónicas, el implementador sólo tiene que hacer que los métodos adecuados produzcan excepciones.
El ejemplo siguiente es una implementación asincrónica de un hipotético procesador masivo de imágenes; a continuación se ofrece un ejemplo de implementación sincrónica. Este código se ha diseñado para realizar una operación de gran consumo en la CPU en todos los archivos de un directorio. Para obtener más información, vea el tema Modelos de diseño para la programación asincrónica.
Imports System
Imports System.IO
Imports System.Threading
Imports System.Runtime.InteropServices
Imports System.Runtime.Remoting.Messaging
Imports System.Security.Permissions
Imports Microsoft.Win32.SafeHandles
Module BulkImageProcAsync
Dim ImageBaseName As String = "tmpImage-"
Dim numImages As Integer = 200
Dim numPixels As Integer = 512 * 512
' ProcessImage has a simple O(N) loop, and you can vary the number
' of times you repeat that loop to make the application more CPU-
' bound or more IO-bound.
Dim processImageRepeats As Integer = 20
' Threads must decrement NumImagesToFinish, and protect
' their access to it through a mutex.
Dim NumImagesToFinish As Integer = numImages
Dim NumImagesMutex(-1) As [Object]
' WaitObject is signalled when all image processing is done.
Dim WaitObject(-1) As [Object]
Structure ImageStateObject
Public pixels() As Byte
Public imageNum As Integer
Public fs As FileStream
End Structure
<SecurityPermissionAttribute(SecurityAction.Demand, Flags:=SecurityPermissionFlag.UnmanagedCode)> _
Sub MakeImageFiles()
Dim sides As Integer = Fix(Math.Sqrt(numPixels))
Console.Write("Making {0} {1}x{1} images... ", numImages, sides)
Dim pixels(numPixels) As Byte
Dim i As Integer
For i = 0 To numPixels
pixels(i) = 255
Next i
Dim fs As FileStream
For i = 0 To numImages
fs = New FileStream(ImageBaseName + i.ToString() + ".tmp", FileMode.Create, FileAccess.Write, FileShare.None, 8192, False)
fs.Write(pixels, 0, pixels.Length)
FlushFileBuffers(fs.SafeFileHandle)
fs.Close()
Next i
fs = Nothing
Console.WriteLine("Done.")
End Sub
Sub ReadInImageCallback(ByVal asyncResult As IAsyncResult)
Dim state As ImageStateObject = CType(asyncResult.AsyncState, ImageStateObject)
Dim stream As Stream = state.fs
Dim bytesRead As Integer = stream.EndRead(asyncResult)
If bytesRead <> numPixels Then
Throw New Exception(String.Format("In ReadInImageCallback, got the wrong number of " + "bytes from the image: {0}.", bytesRead))
End If
ProcessImage(state.pixels, state.imageNum)
stream.Close()
' Now write out the image.
' Using asynchronous I/O here appears not to be best practice.
' It ends up swamping the threadpool, because the threadpool
' threads are blocked on I/O requests that were just queued to
' the threadpool.
Dim fs As New FileStream(ImageBaseName + state.imageNum.ToString() + ".done", FileMode.Create, FileAccess.Write, FileShare.None, 4096, False)
fs.Write(state.pixels, 0, numPixels)
fs.Close()
' This application model uses too much memory.
' Releasing memory as soon as possible is a good idea,
' especially global state.
state.pixels = Nothing
fs = Nothing
' Record that an image is finished now.
SyncLock NumImagesMutex
NumImagesToFinish -= 1
If NumImagesToFinish = 0 Then
Monitor.Enter(WaitObject)
Monitor.Pulse(WaitObject)
Monitor.Exit(WaitObject)
End If
End SyncLock
End Sub
Sub ProcessImage(ByVal pixels() As Byte, ByVal imageNum As Integer)
Console.WriteLine("ProcessImage {0}", imageNum)
Dim y As Integer
' Perform some CPU-intensive operation on the image.
Dim x As Integer
For x = 0 To processImageRepeats
For y = 0 To numPixels
pixels(y) = 1
Next y
Next x
Console.WriteLine("ProcessImage {0} done.", imageNum)
End Sub
Sub ProcessImagesInBulk()
Console.WriteLine("Processing images... ")
Dim t0 As Long = Environment.TickCount
NumImagesToFinish = numImages
Dim readImageCallback As New AsyncCallback(AddressOf ReadInImageCallback)
Dim i As Integer
For i = 0 To numImages
Dim state As New ImageStateObject()
state.pixels = New Byte(numPixels) {}
state.imageNum = i
' Very large items are read only once, so you can make the
' buffer on the FileStream very small to save memory.
Dim fs As New FileStream(ImageBaseName + i.ToString() + ".tmp", FileMode.Open, FileAccess.Read, FileShare.Read, 1, True)
state.fs = fs
fs.BeginRead(state.pixels, 0, numPixels, readImageCallback, state)
Next i
' Determine whether all images are done being processed.
' If not, block until all are finished.
Dim mustBlock As Boolean = False
SyncLock NumImagesMutex
If NumImagesToFinish > 0 Then
mustBlock = True
End If
End SyncLock
If mustBlock Then
Console.WriteLine("All worker threads are queued. " + " Blocking until they complete. numLeft: {0}", NumImagesToFinish)
Monitor.Enter(WaitObject)
Monitor.Wait(WaitObject)
Monitor.Exit(WaitObject)
End If
Dim t1 As Long = Environment.TickCount
Console.WriteLine("Total time processing images: {0}ms", t1 - t0)
End Sub
Sub Cleanup()
Dim i As Integer
For i = 0 To numImages
File.Delete(ImageBaseName + i.ToString + ".tmp")
File.Delete(ImageBaseName + i.ToString + ".done")
Next i
End Sub
Sub TryToClearDiskCache()
' Try to force all pending writes to disk, and clear the
' disk cache of any data.
Dim bytes(100 * (1 << 20)) As Byte
Dim i As Integer
For i = 0 To bytes.Length - 1
bytes(i) = 0
Next i
bytes = Nothing
GC.Collect()
Thread.Sleep(2000)
End Sub
Sub Main(ByVal args() As String)
Console.WriteLine("Bulk image processing sample application," + " using asynchronous IO")
Console.WriteLine("Simulates applying a simple " + "transformation to {0} ""images""", numImages)
Console.WriteLine("(Async FileStream & Threadpool benchmark)")
Console.WriteLine("Warning - this test requires {0} " + "bytes of temporary space", numPixels * numImages * 2)
If args.Length = 1 Then
processImageRepeats = Int32.Parse(args(0))
Console.WriteLine("ProcessImage inner loop - {0}.", processImageRepeats)
End If
MakeImageFiles()
TryToClearDiskCache()
ProcessImagesInBulk()
Cleanup()
End Sub
<DllImport("KERNEL32", SetLastError:=True)> _
Sub FlushFileBuffers(ByVal handle As SafeFileHandle)
End Sub
End Module
using System;
using System.IO;
using System.Threading;
using System.Runtime.InteropServices;
using System.Runtime.Remoting.Messaging;
using System.Security.Permissions;
using Microsoft.Win32.SafeHandles;
public class BulkImageProcAsync
{
public const String ImageBaseName = "tmpImage-";
public const int numImages = 200;
public const int numPixels = 512 * 512;
// ProcessImage has a simple O(N) loop, and you can vary the number
// of times you repeat that loop to make the application more CPU-
// bound or more IO-bound.
public static int processImageRepeats = 20;
// Threads must decrement NumImagesToFinish, and protect
// their access to it through a mutex.
public static int NumImagesToFinish = numImages;
public static Object[] NumImagesMutex = new Object[0];
// WaitObject is signalled when all image processing is done.
public static Object[] WaitObject = new Object[0];
public class ImageStateObject
{
public byte[] pixels;
public int imageNum;
public FileStream fs;
}
[SecurityPermissionAttribute(SecurityAction.Demand, Flags=SecurityPermissionFlag.UnmanagedCode)]
public static void MakeImageFiles()
{
int sides = (int)Math.Sqrt(numPixels);
Console.Write("Making {0} {1}x{1} images... ", numImages,
sides);
byte[] pixels = new byte[numPixels];
int i;
for (i = 0; i < numPixels; i++)
pixels[i] = (byte)i;
FileStream fs;
for (i = 0; i < numImages; i++)
{
fs = new FileStream(ImageBaseName + i + ".tmp",
FileMode.Create, FileAccess.Write, FileShare.None,
8192, false);
fs.Write(pixels, 0, pixels.Length);
FlushFileBuffers(fs.SafeFileHandle);
fs.Close();
}
fs = null;
Console.WriteLine("Done.");
}
public static void ReadInImageCallback(IAsyncResult asyncResult)
{
ImageStateObject state = (ImageStateObject)asyncResult.AsyncState;
Stream stream = state.fs;
int bytesRead = stream.EndRead(asyncResult);
if (bytesRead != numPixels)
throw new Exception(String.Format
("In ReadInImageCallback, got the wrong number of " +
"bytes from the image: {0}.", bytesRead));
ProcessImage(state.pixels, state.imageNum);
stream.Close();
// Now write out the image.
// Using asynchronous I/O here appears not to be best practice.
// It ends up swamping the threadpool, because the threadpool
// threads are blocked on I/O requests that were just queued to
// the threadpool.
FileStream fs = new FileStream(ImageBaseName + state.imageNum +
".done", FileMode.Create, FileAccess.Write, FileShare.None,
4096, false);
fs.Write(state.pixels, 0, numPixels);
fs.Close();
// This application model uses too much memory.
// Releasing memory as soon as possible is a good idea,
// especially global state.
state.pixels = null;
fs = null;
// Record that an image is finished now.
lock (NumImagesMutex)
{
NumImagesToFinish--;
if (NumImagesToFinish == 0)
{
Monitor.Enter(WaitObject);
Monitor.Pulse(WaitObject);
Monitor.Exit(WaitObject);
}
}
}
public static void ProcessImage(byte[] pixels, int imageNum)
{
Console.WriteLine("ProcessImage {0}", imageNum);
int y;
// Perform some CPU-intensive operation on the image.
for (int x = 0; x < processImageRepeats; x += 1)
for (y = 0; y < numPixels; y += 1)
pixels[y] += 1;
Console.WriteLine("ProcessImage {0} done.", imageNum);
}
public static void ProcessImagesInBulk()
{
Console.WriteLine("Processing images... ");
long t0 = Environment.TickCount;
NumImagesToFinish = numImages;
AsyncCallback readImageCallback = new
AsyncCallback(ReadInImageCallback);
for (int i = 0; i < numImages; i++)
{
ImageStateObject state = new ImageStateObject();
state.pixels = new byte[numPixels];
state.imageNum = i;
// Very large items are read only once, so you can make the
// buffer on the FileStream very small to save memory.
FileStream fs = new FileStream(ImageBaseName + i + ".tmp",
FileMode.Open, FileAccess.Read, FileShare.Read, 1, true);
state.fs = fs;
fs.BeginRead(state.pixels, 0, numPixels, readImageCallback,
state);
}
// Determine whether all images are done being processed.
// If not, block until all are finished.
bool mustBlock = false;
lock (NumImagesMutex)
{
if (NumImagesToFinish > 0)
mustBlock = true;
}
if (mustBlock)
{
Console.WriteLine("All worker threads are queued. " +
" Blocking until they complete. numLeft: {0}",
NumImagesToFinish);
Monitor.Enter(WaitObject);
Monitor.Wait(WaitObject);
Monitor.Exit(WaitObject);
}
long t1 = Environment.TickCount;
Console.WriteLine("Total time processing images: {0}ms",
(t1 - t0));
}
public static void Cleanup()
{
for (int i = 0; i < numImages; i++)
{
File.Delete(ImageBaseName + i + ".tmp");
File.Delete(ImageBaseName + i + ".done");
}
}
public static void TryToClearDiskCache()
{
// Try to force all pending writes to disk, and clear the
// disk cache of any data.
byte[] bytes = new byte[100 * (1 << 20)];
for (int i = 0; i < bytes.Length; i++)
bytes[i] = 0;
bytes = null;
GC.Collect();
Thread.Sleep(2000);
}
public static void Main(String[] args)
{
Console.WriteLine("Bulk image processing sample application," +
" using asynchronous IO");
Console.WriteLine("Simulates applying a simple " +
"transformation to {0} \"images\"", numImages);
Console.WriteLine("(Async FileStream & Threadpool benchmark)");
Console.WriteLine("Warning - this test requires {0} " +
"bytes of temporary space", (numPixels * numImages * 2));
if (args.Length == 1)
{
processImageRepeats = Int32.Parse(args[0]);
Console.WriteLine("ProcessImage inner loop - {0}.",
processImageRepeats);
}
MakeImageFiles();
TryToClearDiskCache();
ProcessImagesInBulk();
Cleanup();
}
[DllImport("KERNEL32", SetLastError = true)]
private static extern void FlushFileBuffers(SafeFileHandle handle);
}
El siguiente es un ejemplo sincrónico de la misma hipótesis.
Imports System
Imports System.IO
Imports System.Threading
Imports System.Runtime.InteropServices
Imports System.Runtime.Remoting.Messaging
Imports System.Security.Permissions
Imports Microsoft.Win32.SafeHandles
Module BulkImageProcSync
Dim ImageBaseName As String = "tmpImage-"
Dim numImages As Integer = 200
Dim numPixels As Integer = 512 * 512
' ProcessImage has a simple O(N) loop, and you can vary the number
' of times you repeat that loop to make the application more CPU-
' bound or more IO-bound.
Dim processImageRepeats As Integer = 20
<SecurityPermissionAttribute(SecurityAction.Demand, Flags:=SecurityPermissionFlag.UnmanagedCode)> _
Sub MakeImageFiles()
Dim sides As Integer = Fix(Math.Sqrt(numPixels))
Console.Write("Making {0} {1}x{1} images... ", numImages, sides)
Dim pixels(numPixels) As Byte
Dim i As Integer
For i = 0 To numPixels
pixels(i) = 255
Next i
Dim fs As FileStream
For i = 0 To numImages
fs = New FileStream(ImageBaseName + i.ToString + ".tmp", FileMode.Create, FileAccess.Write, FileShare.None, 8192, False)
fs.Write(pixels, 0, pixels.Length)
FlushFileBuffers(fs.SafeFileHandle)
fs.Close()
Next i
fs = Nothing
Console.WriteLine("Done.")
End Sub
Sub ProcessImage(ByVal pixels() As Byte, ByVal imageNum As Integer)
Console.WriteLine("ProcessImage {0}", imageNum)
Dim y As Integer
' Perform some CPU-intensive operation on the image.
Dim x As Integer
For x = 0 To processImageRepeats
For y = 0 To numPixels
pixels(y) = 1
Next y
Next x
Console.WriteLine("ProcessImage {0} done.", imageNum)
End Sub
Sub ProcessImagesInBulk()
Console.WriteLine("Processing images... ")
Dim t0 As Long = Environment.TickCount
Dim pixels(numPixels) As Byte
Dim input As FileStream
Dim output As FileStream
Dim i As Integer
For i = 0 To numImages
input = New FileStream(ImageBaseName + i.ToString + ".tmp", FileMode.Open, FileAccess.Read, FileShare.Read, 4196, False)
input.Read(pixels, 0, numPixels)
input.Close()
ProcessImage(pixels, i)
output = New FileStream(ImageBaseName + i.ToString + ".done", FileMode.Create, FileAccess.Write, FileShare.None, 4196, False)
output.Write(pixels, 0, numPixels)
output.Close()
Next i
input = Nothing
output = Nothing
Dim t1 As Long = Environment.TickCount
Console.WriteLine("Total time processing images: {0}ms", t1 - t0)
End Sub
Sub Cleanup()
Dim i As Integer
For i = 0 To numImages
File.Delete(ImageBaseName + i.ToString + ".tmp")
File.Delete(ImageBaseName + i.ToString + ".done")
Next i
End Sub
Sub TryToClearDiskCache()
Dim bytes(100 * (1 << 20)) As Byte
Dim i As Integer
For i = 0 To bytes.Length - 1
bytes(i) = 0
Next i
bytes = Nothing
GC.Collect()
Thread.Sleep(2000)
End Sub
Sub Main(ByVal args() As String)
Console.WriteLine("Bulk image processing sample application," + " using synchronous I/O.")
Console.WriteLine("Simulates applying a simple " + "transformation to {0} ""images.""", numImages)
Console.WriteLine("(ie, Sync FileStream benchmark).")
Console.WriteLine("Warning - this test requires {0} " + "bytes of temporary space", numPixels * numImages * 2)
If args.Length = 1 Then
processImageRepeats = Int32.Parse(args(0))
Console.WriteLine("ProcessImage inner loop {0}", processImageRepeats)
End If
MakeImageFiles()
TryToClearDiskCache()
ProcessImagesInBulk()
Cleanup()
End Sub
<DllImport("KERNEL32", SetLastError:=True)> _
Sub FlushFileBuffers(ByVal handle As SafeFileHandle)
End Sub
End Module
using System;
using System.IO;
using System.Threading;
using System.Runtime.InteropServices;
using System.Runtime.Remoting.Messaging;
using System.Security.Permissions;
using Microsoft.Win32.SafeHandles;
public class BulkImageProcSync
{
public const String ImageBaseName = "tmpImage-";
public const int numImages = 200;
public const int numPixels = 512 * 512;
// ProcessImage has a simple O(N) loop, and you can vary the number
// of times you repeat that loop to make the application more CPU-
// bound or more IO-bound.
public static int processImageRepeats = 20;
[SecurityPermissionAttribute(SecurityAction.Demand, Flags=SecurityPermissionFlag.UnmanagedCode)]
public static void MakeImageFiles()
{
int sides = (int)Math.Sqrt(numPixels);
Console.Write("Making {0} {1}x{1} images... ", numImages,
sides);
byte[] pixels = new byte[numPixels];
int i;
for (i = 0; i < numPixels; i++)
pixels[i] = (byte)i;
FileStream fs;
for (i = 0; i < numImages; i++)
{
fs = new FileStream(ImageBaseName + i + ".tmp",
FileMode.Create, FileAccess.Write, FileShare.None,
8192, false);
fs.Write(pixels, 0, pixels.Length);
FlushFileBuffers(fs.SafeFileHandle);
fs.Close();
}
fs = null;
Console.WriteLine("Done.");
}
public static void ProcessImage(byte[] pixels, int imageNum)
{
Console.WriteLine("ProcessImage {0}", imageNum);
int y;
// Perform some CPU-intensive operation on the image.
for (int x = 0; x < processImageRepeats; x += 1)
for (y = 0; y < numPixels; y += 1)
pixels[y] += 1;
Console.WriteLine("ProcessImage {0} done.", imageNum);
}
public static void ProcessImagesInBulk()
{
Console.WriteLine("Processing images... ");
long t0 = Environment.TickCount;
byte[] pixels = new byte[numPixels];
FileStream input;
FileStream output;
for (int i = 0; i < numImages; i++)
{
input = new FileStream(ImageBaseName + i + ".tmp",
FileMode.Open, FileAccess.Read, FileShare.Read,
4196, false);
input.Read(pixels, 0, numPixels);
input.Close();
ProcessImage(pixels, i);
output = new FileStream(ImageBaseName + i + ".done",
FileMode.Create, FileAccess.Write, FileShare.None,
4196, false);
output.Write(pixels, 0, numPixels);
output.Close();
}
input = null;
output = null;
long t1 = Environment.TickCount;
Console.WriteLine("Total time processing images: {0}ms",
(t1 - t0));
}
public static void Cleanup()
{
for (int i = 0; i < numImages; i++)
{
File.Delete(ImageBaseName + i + ".tmp");
File.Delete(ImageBaseName + i + ".done");
}
}
public static void TryToClearDiskCache()
{
byte[] bytes = new byte[100 * (1 << 20)];
for (int i = 0; i < bytes.Length; i++)
bytes[i] = 0;
bytes = null;
GC.Collect();
Thread.Sleep(2000);
}
public static void Main(String[] args)
{
Console.WriteLine("Bulk image processing sample application," +
" using synchronous I/O.");
Console.WriteLine("Simulates applying a simple " +
"transformation to {0} \"images.\"", numImages);
Console.WriteLine("(ie, Sync FileStream benchmark).");
Console.WriteLine("Warning - this test requires {0} " +
"bytes of temporary space", (numPixels * numImages * 2));
if (args.Length == 1)
{
processImageRepeats = Int32.Parse(args[0]);
Console.WriteLine("ProcessImage inner loop � {0}",
processImageRepeats);
}
MakeImageFiles();
TryToClearDiskCache();
ProcessImagesInBulk();
Cleanup();
}
[DllImport("KERNEL32", SetLastError = true)]
private static extern void FlushFileBuffers(SafeFileHandle handle);
}