TService won’t process messages

Question

Hi there, I have created a windows service that uses Windows Messaging System. When I test the app from the debugger the Messages go through nicely but when I install it my messag … asked 14 mins ago

vladimir 1tuga

Answer 1

What do you mean when you say it "uses" Windows Messaging System? Are you consuming or sending Windows Messages?

If you send a Windows message, you need ensure you are doing it correctly. I'd suggest writing a message loop to ensure your messages are being dispatched properly. I'd also suggest reading up on message loops and how they work.

What is a Message Loop (click the title to be taken to the source of this info)

while(GetMessage(&Msg, NULL, 0, 0) > 0)
{
    TranslateMessage(&Msg);
    DispatchMessage(&Msg);
}

1. The message loop calls GetMessage(), which looks in your message queue. If the message queue is empty your program basically stops and waits for one (it Blocks).
2. When an event occures causing a message to be added to the queue (for example the system registers a mouse click) GetMessages() returns a positive value indicating there is a message to be processed, and that it has filled in the members of the MSG structure we passed it. It returns 0 if it hits WM_QUIT, and a negative value if an error occured.
3. We take the message (in the Msg variable) and pass it to TranslateMessage(), this does a bit of additional processing, translating virtual key messages into character messages. This step is actually optional, but certain things won't work if it's not there.
4. Once that's done we pass the message to DispatchMessage(). What DispatchMessage() does is take the message, checks which window it is for and then looks up the Window Procedure for the window. It then calls that procedure, sending as parameters the handle of the window, the message, and wParam and lParam.
5. In your window procedure you check the message and it's parameters, and do whatever you want with them! If you aren't handling the specific message, you almost always call DefWindowProc() which will perform the default actions for you (which often means it does nothing).
6. Once you have finished processing the message, your windows procedure returns, DispatchMessage() returns, and we go back to the beginning of the loop.

Answer 2

Services don't generally receive window messages. They don't necessarily have window handles at all. Even if they do, they run in a separate desktop. Programs cannot send messages from one desktop to another, so a service can only receive messages from another service, or from a program started by a service.

Before Windows Vista, you could have configured your service to interact with the desktop. That makes the service run on the same desktop as a logged-in user, so a program running as that user could send messages to your service's windows. Windows Vista isolates services, though; they can't interact with any user's desktop anymore.

There are many other ways to communicate with services. They include named pipes, mailslots, memory-mapped files, semaphores, events, and sockets.

With a socket, for instance, your service could listen on an open port, and programs that need to communicate with it could connect to that port. This could open the door to remote administration, but you can also restrict the service to listen only for local connections.

All the above is trying to tell you that you're taking the wrong approach. But there's also the matter of the problem at hand. Your program behaves one way in the debugger and another way outside it. How are you debugging the service in the first place, if it's not installed? What user account is your service running as? Your debugger? What debugging techniques have you tried that don't involve the debugger (e.g. writeln to a log file to track your program's actions)?

Answer 3

Thank you all for the answers, the issue was the operating system (vista), i tested the with my windows 2000 and everything works.

thanks for the light Rob.