Click here to Skip to main content
Click here to Skip to main content
Go to top

Interop: Waiting in C# on External Win32 Events

, 31 Aug 2005
Rate this:
Please Sign up or sign in to vote.
An article on catching external process events from within .NET (C#) code.

Sample Image - MfcEventSource.gif

Introduction

I found several examples of how to Open and Set named Win32 events from within .NET code, but I also needed to catch Win32 events in my .NET application. That is, I wanted to do the equivalent of Win32's (C++) WaitForMultipleObjects(), only in C#. I found no examples of this at Microsoft or on the Internet at large. All of the discussion of WaitHandle and its derivatives, AutoResetEvent and ManualResetEvent only talked about multi-threading, not about inter-process communication. I was left unsure if it was possible (or at any rate whether it was simple, most things are possible with enough contortions and excursions into managed C++...); so I gave it a try. The result? It's remarkably simple ...

Background

Our environment uses an executive process to control which other processes are running, and in what state they are running, e.g. as "primary" or "secondary", the latter being a warm back up that can be quickly switched over to primary should the first copy fail.

There are a handful of named events used to communicate between the executive and the worker processes, e.g. one event to tell them to transition from "secondary" to "primary" and another to tell them to shut down. This executive process uses well known environment variables to communicate the names of the events to its worker processes.

Historically, all these processes were Win32/MFC applications. Now some are becoming .NET apps, but it is most convenient to keep the same communications mechanism for the time being.

Using the code

Since the way to do this is so simple, I'll just show the code. The bold part was to just go ahead and assign the result from the Win32 OpenEvent() call to an AutoResetEvent.Handle property:

uint unEventPermissions = 2031619;
// Same as EVENT_ALL_ACCESS value
// in the Win32 realm IntPtr hEvent = IntPtr.Zero; 

// Get a handle to the Win32 Event.
// The name, "MfcEventSource", is known in advance 
hEvent = OpenEvent(unEventPermissions, 
                   false, "MfcEventSource"); 
if (IntPtr.Zero == hEvent) 
{
  Console.WriteLine("OpenEvent failed"); 
  return; // Exit 
}
// Create an AutoResetEvent object to wrap
// the handle we got from OpenEvent 
AutoResetEvent arEvent = new AutoResetEvent(false); 
// Set the Handle property to the external event HANDLE 
arEvent.Handle = hEvent;

That's it! Now you can put this AutoResetEvent object into a WaitHandle array and use WaitAny() (or use WaitOne() directly on the AutoResetEvent object or use WaitAll(), etc.). Here's an example:

WaitHandle[] waitHandles;
waitHandles = new WaitHandle[1];
//Put it in our array for WaitAny()
waitHandles[0] = arEvent;
bool bDone = false;
while ( !bDone )
{
  Console.WriteLine("Top of while");
  int waitResult = WaitHandle.WaitAny(waitHandles, 2000, false);
  //For timeout, just loop and wait again
  if (waitResult == WaitHandle.WaitTimeout)
  {
    Console.WriteLine(" WaitAny timed out.");
  }
  else if (0 == waitResult)
  {
    Console.WriteLine("0 == waitResult. Yippee !!!");
    // Do Something
  }
  else if (1 == waitResult)
  {
    Console.WriteLine("1 == waitResult !!!");
    // Do Something Else
  }
  else
  {
    Console.WriteLine("Error else");
  }
}

If you download the demo project you'll actually get three solutions, one that is the MFC/Win32 (C++) application that is the source of the named event, another that is the .NET (C#) event sink application that opens and waits on the external event, and a third that is an MFC/Win32 (unmanaged C++) event sink application, it is the logical equivalent of the C# app. Be sure to run the MfcEventSource program first, then start either of the other two.

Points of Interest

I guess that Microsoft can't be expected to provide examples and practical descriptions of all the available classes, but in this case the fact that WaitHandle objects are only described for use with multi-threading but there is no mention of multi-process usage seems misleading. On the other hand, once you see what is available on these classes and boldly go ahead and use those features, it seems to work quite well. Any one knows any reason to fear otherwise? Thanks.

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.

A list of licenses authors might use can be found here

Share

About the Author

Chip Patton
Web Developer
United States United States
Chip Patton
Software Engineer
Intergraph Public Safety

Comments and Discussions

 
QuestionHow to track the windows login event? Pinmemberjasnavp10-Feb-08 23:52 
GeneralHandle Mutiple Named Events PinmemberAshu v23-Sep-07 21:11 
General.NET 2.0 Alternative PinmemberLee Clark27-Jan-07 16:02 
GeneralHandle leak [modified] PinmemberLeo Davidson4-Jul-06 7:13 
QuestionHow do you learn/determine an external event's name? Pinmemberbarnabya3-May-06 23:55 
AnswerRe: How do you learn/determine an external event's name? PinmemberChip Patton4-May-06 10:37 
GeneralRe: How do you learn/determine an external event's name? Pinmemberbarnabya4-May-06 10:43 
GeneralUse CreateEvent if you don't know the sequence of starting Pinmemberihristov12-Dec-05 7:19 
GeneralI need help PinmemberYuragel31-Oct-05 2:52 
Confused | :confused: Confused | :confused: Confused | :confused: Sorry for maybe non relevant question.
I have an unmanaged cpp dll and I need to create and set mine event in this dll but handle for this event should be in managed vb.net project.
How do I catch created by myself unmanaged event in managed vb.net project ?
thanks in advance

 
Geyur
GeneralRe: I need help PinmemberChip Patton31-Oct-05 6:26 
GeneralWin32 events PinmemberGil Orlev22-Oct-05 21:24 
GeneralRe: Win32 events PinmemberChip Patton31-Oct-05 6:12 
GeneralPInvoke Alternative PinmemberRyan L. Schneider31-Aug-05 12:23 
GeneralRe: PInvoke Alternative PinmemberChip Patton1-Sep-05 4:13 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Mobile
Web03 | 2.8.140916.1 | Last Updated 31 Aug 2005
Article Copyright 2005 by Chip Patton
Everything else Copyright © CodeProject, 1999-2014
Terms of Service
Layout: fixed | fluid