Issue with windows service waiting for a named event, using EventWaitHandle.

Question

I'm currently developing a windows service with c# and .net framework 4.5 to extend the functionality of an existing propietary application, this service blocks on an EventWaitHandleClass (msdn link) waiting for a named event signaled from the main application. Something like this:

bool boolWithFalse = false;
string eName = "notification_event";
string usr = Environment.UserDomainName + "\\" + Environment.UserName;
EventWaitHandleSecurity security = new EventWaitHandleSecurity(); //*
EventWaitHandleAccessRule rule = new EventWaitHandleAccessRule(usr, EventWaitHandleRights.Synchronize, AccessControlType.Allow);
security.AddAccessRule(rule);
EventWaitHandle handle = new EventWaitHandle(false, EventResetMode.ManualReset, eName, out boolWithFalse, security);

//... some non relevant code lines here

//This is where the it locks waiting for the named event
var w = EventWaitHandle.WaitAny(new[] { handle }, Timeout.Infinite);

*: EventWaitHandleSecurity MSDN

Now this works like a charm if i execute my program as a console application, i can easily catch events from the main application and handle them as i intend, BUT, when i install the application as a service it locks waiting for this same named event but never receive the signal. The service is set to run using the NT AUTHORITY\LOCALSERVICE account, i've already tried using my own account (wich the progam uses while running as a console application) and yet nothing happens.

If it helps the application that originates the signal is running under my own account. I appreciate any help as i'm a complete beginner developing desktop applications for windows.

Answer 1

You got lost in the security hoopla. Two problems. The first one is that somebody has to create the event and somebody else has to open it so both components share the same event object. One of them has to use the EventWaitHandle constructor, the other has to call the EventWaitHandle.OpenExisting() method. The normal way is for the service to create the event and for the UI program to open it.

Next problem is the event object visibility. Windows implements namespaces for named operating system objects, pretty similar to how you use namespaces in the C# language. The root namespace is named by the session. And a service runs in a different session than the user's desktop programs. To get the desktop session program to see the event created in the service session, you have to use a "global" event name. Which looks like this:

 string eName = "Global\\notification_event";

Do be careful of how you name your globally visible named event. There's another programmer somewhere someday that thinks that "notification_event" is a good choice for a name. You don't want to meet him. A {guid} is a good name, you get one from Tools + Create GUID. It is unique in the known universe, possibly beyond.