Using nHibernate in a windows service

I want to use nHibernate in a windows service. If the systems boots, it might start my service before the database. In that case, configuration of nHibernate fails and the service crashes. So now I'm wondering how I can check if开发者_如何学Python the database service has already been started. In case it has not yet started, my service should wait a bit and try again later.

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If your service always runs on the same machine as SQL Server, You should be using ServiceInstaller.ServicesDependedOn to tell Windows(SCM) that you depend on 'MSSQLSERVER' (the name of service that runs SQL Server).

From MSDN:

A service can require other services to be running before it can start. The information from this property is written to a key in the registry. When the user (or the system, in the case of automatic startup) tries to run the service, the Service Control Manager (SCM) verifies that each of the services in the array has already been started.

ServiceInstaller is the class that is used by InstallUtil when it installs your service. Other installation packages including InstallShield also support this windows functionality. Equivalent SC command.

So your service will only start after SQL Server is already running. But even in this case, it might still be a good idea to offload all potentially long running startup procedures to the background thread. Do as little as possible in OnStart method. Ideally you would just spawn a new initialization thread that would take care of NHibernate session factory initialization. If for some reasons you still want to do this in OnStart, then you should consider retrying NHibernate initialization and calling ServiceBase.RequestAdditionalTime to avoid:

Error 1053: The service did not respond to the start or control request in a timely fashion.

Ideally your service should not depend on the database availability because it might be running on a remote machine. The service is an 'always on' process that should tolerate intermittent database connectivity issues.

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No clue if there are better ways, but in your service startup, check for the system uptime. If this is less then let's say 5 minutes, wait for (5 minutes - Uptime) and after that start the rest of the service as you normally would.

See the following for Calculating server uptime gives "The network path was not found"

This is not a solution however for when your service tries to connect to a SQL which is down, however if this happens you want to handle the exception and actually be notified that the SQL is down. Very unlikely you want the service to keep trying without you yourself beeing aware the SQL is down.

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You could use ServiceController class and call its static method GetServices() to get the list of services. It will give an array of services, find the right one and check its status.

See ServiceController on MSDN

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Currently I am making sure I can establish a connection to the database needed and running a default query (configurable). If this is successful I proceed to start the service.

What I've found in some cases is that even if the MSSQL service is started it doesn't guarantee that you can connect to it and execute queries against it.