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Windows service to do job every 6 hours

I've got a windows service with only two methods - one private method DoWork(), and an exposed method which calls DoWork method. I want to achieve the following:
Windows service runs DoWork() method every 6 hours
An external program can also invoke the exposed method which calls DoWork() method. If the service is already running that method called from the service, DoWork() will again be invoked after the current method ends.
What's the best approach to this problem? Thanks!

An alternative approach would be to make use of a console application which can be scheduled by Windows task scheduler to run every 6 hours. In that case you don't waste resources to keep the Windows service running the entire time but only consume resources when needed.
For your second question: when you take the console app approach you can have it called by making use of Process.Start for example.

If the purpose of your application is only to run a specific task every six hours, you might be better off creating a command line application and creating a scheduled task that Windows runs automatically. Obviously, you could then manually start this application.
If you're still convinced you need a service (and honestly, from what I've seen so far, it sounds like you don't), you should look into using a Timer, but choose your timer carefully and read this article to get a better understanding of the timers built into .NET (Hint: Pay close attention to System.Timers.Timer).
To prevent reentry if another method tries to call DoWork() while the process is in the middle of performing its operation, look into using either a Mutex or a Semaphore.

there are benefits and drawbacks either way. my inclination with those options is to choose the windows service because it makes your deployment easier. scheduling things with the windows task scheduler is scriptable and can be automated for deployment to a new machine/environment, but it's still a little more nonstandard than just deploying and installing a windows service. you also need to make sure with task scheduler it is running under an account that can make the webservice call and that you aren't going to have problems with passwords expiring and your scheduled tasks suddenly not running. with a windows service, though, you need to have some sort of checking in place to make sure it is always running and that if it restarts that you don't lose hte state that lets it know when it should run next.
another option you could consider is using nservicebus sagas. sagas are really intended for more than just scheduling tasks (they persist state for workflow type processes that last for more than the duration of a single request/message), but they have a nice way of handling periodic or time-based processes (which is a big part of long running workflows). in that a saga can request that it get back a message from a timeout manager at a time it requests. using nservicebus is a bigger architectural question and probably well beyond the scope of what you are asking here, but sagas have become how i think about periodic processes and it comes with the added benefit of being able to manage some persistent state for your process (which may or may not be a concern) and gives you a reason to think about some architectural questions that perhaps you haven't considered before.

you can create a console application for your purpose. You can schedule the application to run every 6 hours. The console will have a default method called on application start. you can call your routine from this method. Hope this helps!!

Best method to call WCF services at interval

I have several WCF services and I want to execute methods in them at specific intervals.
For example, call Service1.DoSomeWork every 5 minutes and Service2.DoSomeWork every 10 minutes. I also want Windows client applications to be able to call the DoSomeWork methods at any time.
What is the best way to implement this?
I have complete control over the server so using Scheduled Tasks is possible but I wonder if using a Workflow in AppFabric is better or using a timer in the service itself?

Check out this post. I answered a question a while ago where the developer want to "Do something" at an interval in a windows service. I gave a pretty detailed code sample for scheduling activity within a Windows Service as recommended by other posted earlier in this thread.
how to make service act dynamically based on service running condition

I'm not familiar with AppFabric but if I were you, I will use the timer since your requirement sounds simple.

If I were your ,
I create a windows service in the server .
So that I can do anything at specific intervals....

Developing a polling mechanism

In C#, what is the best way to create a polling mechanism? So I have some code which can periodically do some action.
This is for web services so any UI-related solutions won't apply.
Thanks

If you are saying that you have a web service which is supposed to periodically take some action on it's own, then I think you haven't quite got the web services model. Web services are supposed to sit there (just like a web page) until something kicks it off.
Otherwise you are dealing with a very brittle situation where anything could cause it to just stop.
If you have a bit of code that needs to run on a timer, then you should investigate placing that code in a windows service (not to be confused with Web Service). That's what they are for.

"code which can periodically do some action" is called a "Timer". Search MSDN, you'll find three or four classes for the purpose, several of which are non-gui (System.Threading.Timer comes to mind).
EDIT: To whom do the changes need to be visible? If they are only visible to other consumers of the web service, then one approach is for each incoming request can check whether a periodic action is overdue and perform it. However, you shouldn't do things this way if (1) the changes need to be visible to e.g. other clients of the same database, or (2) the periodic changes need greater permissions than arbitrary incoming requests. Also, the periodic actions might be interrupted if the client cancels their request, and doing the actions might significantly delay the response to the client. For these reasons I don't recommend adding periodic processing to normal request/response processing.

Take a look at the System.Threading.Timer class. This makes periodic calls to a method you supply. These calls are made on a separate thread (a thread in the thread pool).

You'll want to use a timer.
There are a few timers in the .NET framework, including:
System.Timers.Timer
System.Threading.Timer
System.Windows.Forms.Timer
See this article for help choosing the right one: Comparing the Timer Classes in the .NET Framework Class Library

It sounds like you want a Timer, but that does not make sense to use in a Web service. It would make more sense if the timer was in a client. What clients use your web service?

Windows service that will run every hour

I m able to build a windows service and install it.
I m curious how can i run this service every hour ? I want it to run every hour periodically.
I also need to know the hour range that it s running so that I can store it somewhere.
How can i do that?
Edit : This service will be installed on many machines, therefore, I dont want to create a scheduled task say on 100 servers.

If you want a task to run on a regular interval as opposed to constantly, you should look into using the Task Scheduler.
If you need your code to be a service, but to be "activated" every hour, the easiest approach would be to make your service a COM object and have a simple task scheduled every hour that invokes a jscript/vbscript that creates your COM object and calls simple method on it.
The alternative is to use any of the wait APIs to "waste" an hour without consuming cycles.
Note that you also have to consider some interesting design decisions that depend on what your scenario is:
how is your service going to be started if it crashes or is stopped by the user?
if you are started after more than an hour, should you run again or do you need to wait to get on the exact hourly schedule?
how do you keep track of the last "activation" time if the timezone or the day-light saving time has changed while you were not active?
does your service prevent the computer from going to sleep/hibernate on idling or when the laptop cover is closed? if not, do you need to awake the computer on the hour to get your service working on your schedule?
Some of those are taken care of by the task scheduler, so I would strongly recommend going that route vs. waiting for an hour in your code.

You could create a scheduled task that runs every hour, to either run the service or send a message to "wake it up". Then, either pass in the current time in the scheduled task request, or just have your program pick up the current time when it wakes up.
Task Scheduler Managed Wrapper can help you set this up programmatically; you can google for other resources as well.

There are a couple options.
You could sleep for an hour.
You might be better suited for a Scheduled Task, not a service.

Thread.Sleep(1000*60*60);

Thread.Sleep(TimeSpan.FromHours(1));
code more readable this way

Thread.Sleep() solution will make sure that your service will run in one hour intervals, not every hour i.e. each task will be started at 1 hour + time to run the task. Consider using a Timer within your service. This will be a more robust solution since you have a control when to run a task, monitor its progress etc. Just remember that each Timer event will be fired in a different thread and if the task takes longer than one hour to run you might have to wait for the first task to finish to avoid concurrent tasks.

Task schedulers may be a good idea but services are designed to do this. Services gets installed easily and logs things properly. All you need to do is, at start of service, you can install a system timer (System.Threading.Timer) or there is also one more timer.

Executing an application after a period of time

I'm writing a small app that needs to be executed once a week.
I could write it as a service that runs constantly but only executes the task that I need it to once a week, but that seems like overkill.
Is there another way of executing an application once every x period of time?
I'm looking for a solution that doesn't involve user interaction.

You can always use Windows Scheduled Tasks. They can be ugly, but effective.

You could use the Windows Task Scheduler. It was designed with this scenario in mind.

You can use Windows Scheduler for planning execute app once a week.

Under windows you can use the at utility.

You can use the Windows Task Scheduler in the Control Panel. Just set up a task to run your application on the specified day. You can even tell it to run as a certain user if you want.

If you need full control on the process (result values, parameters to be provided, etc), I would suggest you to create your own task scheduler, where you can use the cron algorithm to schedule the time you want execute your task.
I know it may sounds overkill to create a service to run once a week, but if you make a generic scheduler, you will be able to reuse your schedule for other purposes.
I created this scheduler in the past, and it has been used for years in production. I implemented the cron algorithm in .Net, based in the open source algorithm that one developer (Artif Aziz) wrote. Check out my blog for more information on this:
CronTab schedule parser algorithm
If you think in a higher level (enterprise level), you could consider buying Control-M, one of the most powerful scheduler tools I have ever used, however it is quite expensive.
Cheers!
Roberto.