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Event notification on streams during long reads or writes

, 11 Aug 2003
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An article on event notification for operations on large streams...

Sample screenshot

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.

Diagram

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 ) ;

    }
}

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

Jim Wiese (aka Spunk)
Web Developer
United States United States
I generally attend most of the Microsoft DevDays in the south bay area (CA) and BayArea.NET functions in case any of you attend those as well. I'm always up for a lively disucussion about new technologies in the industry, Microsoft or not. Send me a note if you attend!

Comments and Discussions

 
QuestionCool idea what about the asynchronous case? Pinmembermkonrad19-Aug-03 21:17 
GeneralThanks! Pinmembersichbo218-Aug-03 16:16 
EventStream sounds pimpin', I think I'll use it in my current project--thanks for pointing it out.

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