使用 .NET的IO(2) Paul_Ni（原作）（补充）

答案：
[C#]
using System;
using System.IO;
using System.Threading;
using System.Runtime.InteropServices;
 
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;
}
 
public static void MakeImageFiles()
{
int sides = (int) Math.Sqrt(numPixels);
Console.Write("Making "+numImages+" "+sides+"x"+sides+" images...  ");
byte[] pixels = new byte[numPixels];
for(int i=0; i<numPixels; i++)
pixels[i] = (byte) i;
 
for(int i=0; i<numImages; i++) 
{
FileStream fs = new FileStream(ImageBaseName+i+".tmp", FileMode.Create,
   FileAccess.Write, FileShare.None, 8192, false);
   fs.Write(pixels, 0, pixels.Length);
   FlushFileBuffers(fs.Handle);
   fs.Close();
   }
   Console.WriteLine("Done.");
}
 
public static void ReadInImageCallback(IAsyncResult asyncResult)
{
ImageStateObject state = (ImageStateObject) asyncResult.AsyncState;
//Console.WriteLine("Image "+state.imageNum+" was read 
   "+(asyncResult.CompletedSynchronously ? "synchronously" : 
      "asynchronously"));
Stream stream = state.fs;//(Stream) asyncResult.AsyncObject;
int bytesRead = stream.EndRead(asyncResult);
if (bytesRead != numPixels)
throw new Exception("In ReadInImageCallback, got wrong number of bytes 
   from the image!  got: "+bytesRead);
 
ProcessImage(state.pixels, state.imageNum);
stream.Close();
 
// Now write out the image.  
// Using asynchronous IO here appears not to be best practice.  It ends up
// swamping the threadpool, since the threadpool threads are blocked 
// on IO requests that we've 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;
 
// Record that an image is done 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 "+imageNum);
 
// Do some CPU-intensive operation on the image.
for(int i=0; i<processImageRepeats; i++)
   for(int j=0; j<numPixels; j++)
      pixels[j] += 1;
 
Console.WriteLine("ProcessImage "+imageNum+" done.");
}
 
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 file stream 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: "+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 
         async IO");
     
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