Windows Services and stdout does not seem to work

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Hi,

Using a toolkit which get a reference to std::out and then outputs some debug. This causes a 0xc0000005. I am not the best at windows, my experience is more on a linux platform.

I have manage to port the software to windows as an .exe and it works fine. However when I wrapped it in the sample windows service code from the msdn it fault on outputting to stdout.

The offending lines were in the dcmtk consap.cc

log4cplus::tostream&amp; output = (logToStdErr ? ofConsole.lockCerr() : ofConsole.lockCout());
output << "I will not crash"

Which is think is roughly cout << "I will not crash" or cerr << "I will not crash"

Iain

Posted 3-Mar-11 18:25pm

Iain Wiseman

Updated 3-Mar-11 18:47pm

Sandeep Mewara

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Sergey Alexandrovich Kryukov · Answer 1 · 2011-03-03T18:51:00

Windows Service is not supposed to work this way. You can write to a file (be careful about permission, the services are run in special accounts, depending on how to install it, but you can install it to run as an authenticated user as well), or the System Log (which is the preferred method of logging guaranteed by OS).

A Windows Service typically responds and communicates through network sockets or named pipes, but any other IPC primitive can be used. When a process is run as a Windows Service, it does not work with UI or console directly, for a good reason: such process runs when nobody is logged in, when no UI or console is available.

Sometimes some UI is used to control a running Windows Service process, but — here is how: you have a separate process which act as a special client used to control the Windows Server process. It can be even built as the same application as the Windows Service application (this is my approach), but still run as a separate process, in a special interactive mode.

For example, Apache for Windows has an application sitting in the System Tray; this UI-enabled process is used to communicate with Apache Windows Service to track its status and send commands like Start/Stop/Restart.

So, the resolution of your problem would be to re-design your code to work in the manner I just described. Right approach would be a thorough separation of pure service code from the code depending on the platform and interaction with OS and controlling process.

[EDIT]
If you need to wait for files, don't do spin-wait! You can do it in event-driven way using the class System.IO.FileSystemWatcher; it will notify you about file system changes you want to subscribe for.

—SA

Espen Harlinn · Answer 2 · 2011-03-03T21:40:00

Hi Iain,

Take a look at ACE[^]

It has a very useful logging framework, including the ability to write log output to another console process - something that is very useful when you are working on windows services.

Under the $(ACE_ROOT)\examples\NT_Service you will find a very nice example illustrating both logging, and how the framework can be used to implment a windows service. The framework also has a very flexible mechanism for dealing with configuration files :)

To monitor a directory you can use ReadDirectoryChangesW[^] - this the windows api implmenting the functionality used by the System.IO.FileSystemWatcher class mentioned by SAKryukov

Update
Leave your working executable as is, and use CreateProcess[^] from a simple windows service, passing a STARTUPINFO[^] with valid handles for hStdOutput and hStdError.

Use CreateFile[^] to create the handles hStdOutput and hStdError, this will cause your existing program to write to those handles for stdout and stderr, respectively.

Use CreateEvent to create an event object to set during the stop event and monitor the process handle and the event to determine when to stop your program.

You can read more about Windows services here[^]

Regards
Espen Harlinn

Windows Services and stdout does not seem to work

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