overlooping in C#

问题:

I am going to create a system service in C#.

In the onstart section I would like to loop every 30 seconds and query a mysql database. If numrows are greater than 0 I will process some faxes using the faxcom library.

My question is: Would looping every 30 seconds exhaust the program/computer? What would be the best function/method to use for the loop and sleep? Do you have any example code for the loop and sleep?

回答1:

Using Thread.Sleep() would be a bad solution, because even while sleeping your thread is active. Use Timer class instead and handle its Elapsed event.

This article examines different ways to tackle the periodical execution of your service.

Here is what your OnStart method might look like:

using System.Timers; 

private timer = new Timer();

protected override void OnStart(string[] args)
{
 timer.Elapsed += new ElapsedEventHandler(OnElapsedTime);
 timer.Interval = 30000; // every 30 seconds
 timer.Enabled = true;
}

Private void OnElapsedTime(object source, ElapsedEventArgs e)
{
   // Execute your code here
}

回答2:

I wouldn't use looping constructs for such a thing.

I would use one of the timer controls in the BCL and set it to fire every 30 seconds.

As for the question of if this is "too much", the answer entirely depends on the amount of work being done and the load it generates.

回答3:

No, you would not be using the CPU, because sleeping threads are not scheduled for execution until their sleep time expires. Use Thread.Sleep to make the current thread sleep for timeout miliseconds. Something like:

while(!stop) // boolean variable to indicate when to stop the service.
{
    Thread.Sleep(30000);
    // do work
}

You will, of course, need to run this on a separate thread, otherwise you will block the main thread.

回答4:

I would avoid using System.Timers.Timer in your case solely because you are writing a Windows Service. While you can use it, you won't have a GUI available and therefore don't need anything that this timer would expose as if you were using a GUI (it inherits from System.ComponentModel.Component for this reason). It's pretty simple to use.