Question

How does a C# Timer Object decide when an elapsed amount of time has occurred?

I am wondering if it simply loops or is more intelligent than this.

Also, it would be good to know where to find the C# Source Code to have a look through.

Answer 1

The .NET BCL has at least two classes providing timers:

• System.Threading.Timer
• System.Timers.Timer

However, the second class is implemented using the first. The first class uses some kind of native Win32 timer and Hans Passant has provided more information about the mechanism used. In the BCL source code the timer is implemented using an internal class named TimerQueue. The implementation of the TimerQueue class has this comment:

TimerQueue maintains a list of active timers in this AppDomain. We use a single native timer, supplied by the VM, to schedule all managed timers in the AppDomain.

So basically the AppDomain has a single time source implemented using unmanaged code. See Hans Passant’s answer for more information on that.

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Also, it would be good to know where to find the C# Source Code to have a look through.

I use JetBrains dotPeek. It can be configured to retrieve source files from Microsoft if they exist. Simply load in the version of .NET you want to examine, hit Ctrl+T, type “Timer”, select the specific class you want and it will download the source if it exists. Otherwise you will see a decompiled version (depending on your configuration).

Note that this tool will only allow you to decomple managed code and to fully understand the implementation of timers in .NET you need to be able to peek further into unmanaged code.