Event notification on streams during long reads or writes

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Introduction

Sometimes during programming, there are some methods that take a stream and then perform some function on it. Usually, if the stream is fairly large, then the method may not return for an extreme amount of time (e.g. ~20 minutes for SHA1 calculation on 2 GB file across a network). Some applications would simply like to get notified that there was some activity and hopefully the amount of activity. Being notified that a block of bytes is about to, or has been read would solve this problem. Thus, the EventStream reader attempts to solve this problem. See the example for more information.

Using the code

Below is an example usage of this class, to be notified during a potentially long SHA1 calculation.

class ExampleNotifyClass
{
    public int timesNotified = 0 ;

    public void SectionWasRead( byte[] buff, int index, int count ) 
    {
        Console.WriteLine("Section read: {0}", count ) ;
        timesNotified++ ;
    }


    ///

    /// Main

    ///

    public static void Main() {

      // Create the sample data to read

      MemoryStream mem  = new MemoryStream() ;
      StreamWriter writer = new StreamWriter(mem, Encoding.UTF8) ;

      // Populate the stream

      for( int i = 0 ; i < 16 * 777 ; i++ ) 
      {
        writer.WriteLine( "{0}", i % 10 ) ;
      }

      // Reset the pointer in the stream

      mem.Seek( 0, SeekOrigin.Begin ) ;

      // Create a sample class 

      ExampleNotifyClass toNotify = new ExampleNotifyClass(); 
      EventStream toRead = new EventStream( mem ) ;
      toRead.AfterBlockRead += new 
        EventStream.AfterBlockHandler(toNotify.SectionWasRead ) ;
      toRead.BlockEventSize = 8192 ; 
        // Get notified for every 8192 bytes read


      SHA1 sha = new SHA1Managed() ;

      // Actual work is done here

      byte[] hash = sha.ComputeHash( toRead ) ;

      Console.WriteLine( "Our class was notified {0} times.", 
                             toNotify.timesNotified ) ;

    }
}