Develop Reference

Service stopping unexpectedly probably due to GC on Timer

My company has developed a Windows Service Application and it was installed in some customers.
They are complaining that the Service stops after continuously running for a few days.
I can't reproduce the error and I do not have any stack trace. All I have is a generic message in Event Viewer:
The 'myservicename' service terminated unexpectedly. It has done this 1 time(s).
My code:
private System.Timers.Timer myTimer;
private readonly Queue<FileInfo> MyQueue = new Queue<FileInfo>();
protected override void OnStart(string[] args)
{
myTimer = new System.Timers.Timer(1000 * 60 * 1); // 1 min
myTimer.Elapsed += new ElapsedEventHandler(MyMethod);
myTimer.Start();
SomeSafeTasks();
try
{
CreateSomeThreads();
}
catch(Exception)
{
//log
}
}
public void MyMethod()
{
lock (MyQueue) // there are other places with lock
{
if(MyQueue.Count == 0)
{
// code with try catch
}
}
}
I believe that the error is related with the Timer being GC'ed.
Does it make sense? The code above may break after running some days?
How do I estimate when it will break? It is strange for me that it runs for a week. I would expect that it would be GC'ed in 15 minutes or 1 hour.
Is it 100% safe to add GC.KeepAlive(myTimer) after myTimer.Start()?
Will it run forever or do I need to call GC.KeepAlive sometimes?

Single threaded timer

I wanted a timer with the following properties:
No matter how many times start is called, only one call back thread is ever running
The time spent in the call back function was ignored with regards to the interval. E.g if the interval is 100ms and the call back takes 4000ms to execute, the callback is called at 100ms, 4100ms etc.
I couldn't see anything available so wrote the following code. Is there a better way to do this?
/**
* Will ensure that only one thread is ever in the callback
*/
public class SingleThreadedTimer : Timer
{
protected static readonly object InstanceLock = new object();
//used to check whether timer has been disposed while in call back
protected bool running = false;
virtual new public void Start()
{
lock (InstanceLock)
{
this.AutoReset = false;
this.Elapsed -= new ElapsedEventHandler(SingleThreadedTimer_Elapsed);
this.Elapsed += new ElapsedEventHandler(SingleThreadedTimer_Elapsed);
this.running = true;
base.Start();
}
}
virtual public void SingleThreadedTimer_Elapsed(object sender, ElapsedEventArgs e)
{
lock (InstanceLock)
{
DoSomethingCool();
//check if stopped while we were waiting for the lock,
//we don't want to restart if this is the case..
if (running)
{
this.Start();
}
}
}
virtual new public void Stop()
{
lock (InstanceLock)
{
running = false;
base.Stop();
}
}
}

Here's a quick example I just knocked up;
using System.Threading;
//...
public class TimerExample
{
private System.Threading.Timer m_objTimer;
private bool m_blnStarted;
private readonly int m_intTickMs = 1000;
private object m_objLockObject = new object();
public TimerExample()
{
//Create your timer object, but don't start anything yet
m_objTimer = new System.Threading.Timer(callback, m_objTimer, Timeout.Infinite, Timeout.Infinite);
}
public void Start()
{
if (!m_blnStarted)
{
lock (m_objLockObject)
{
if (!m_blnStarted) //double check after lock to be thread safe
{
m_blnStarted = true;
//Make it start in 'm_intTickMs' milliseconds,
//but don't auto callback when it's done (Timeout.Infinite)
m_objTimer.Change(m_intTickMs, Timeout.Infinite);
}
}
}
}
public void Stop()
{
lock (m_objLockObject)
{
m_blnStarted = false;
}
}
private void callback(object state)
{
System.Diagnostics.Debug.WriteLine("callback invoked");
//TODO: your code here
Thread.Sleep(4000);
//When your code has finished running, wait 'm_intTickMs' milliseconds
//and call the callback method again,
//but don't auto callback (Timeout.Infinite)
m_objTimer.Change(m_intTickMs, Timeout.Infinite);
}
}

The .NET Framework provides four timers. Two of these are general-purpose multithreaded
timers:
System.Threading.Timer
System.Timers.Timer
The other two are special-purpose single-threaded timers:
System.Windows.Forms.Timer (Windows Forms timer)
System.Windows.Threading.DispatcherTimer (WPF timer)
The last 2 are designed to eliminate thread-safety issues for WPF and Windows Forms applications.
For example, using WebBrowser inside a timer to capture screenshots from webpage needs to be single-threaded and gives an error at runtime if it is on another thread.
The single-thread timers have the following benefits
You can forget about thread safety.
A fresh Tick will never fire until the previous Tick has finished
processing.
You can update user interface elements and controls directly from
Tick event handling code, without calling Control.BeginInvoke or
Dispatcher.BeginIn voke.
and main disadvantage to note
One thread serves all timers—as well as the processing UI events.
Which means that the Tick event handler must execute quickly,
otherwise the user interface becomes unresponsive.
source: most are scraps from C# in a Nutshell book -> Chapter 22 -> Advanced threading -> Timers -> Single-Threaded Timers

For anyone who needs a single thread timer and wants the timer start to tick after task done.
System.Timers.Timer could do the trick without locking or [ThreadStatic]
System.Timers.Timer tmr;
void InitTimer(){
tmr = new System.Timers.Timer();
tmr.Interval = 300;
tmr.AutoReset = false;
tmr.Elapsed += OnElapsed;
}
void OnElapsed( object sender, System.Timers.ElapsedEventArgs e )
{
backgroundWorking();
// let timer start ticking
tmr.Enabled = true;
}
Credit to Alan N
source https://www.codeproject.com/Answers/405715/System-Timers-Timer-single-threaded-usage#answer2
Edit: spacing

Look at the [ThreadStatic] attribute and the .Net 4.0 ThreadLocal generic type. This will probably quickly give you a way to code this without messing with thread locking etc.
You could have a stack inside your time class, and you could implement a Monitor() method that returns a IDisposable, so you can use the timer like so:
using (_threadTimer.Monitor())
{
// do stuff
}
Have the timer-monitor pop the the interval timestamp off the stack during Dispose().
Manually coding all the locking and thread recognition is an option as has been mentioned. However, locking will influence the time used, most likely more than having to initialize an instance per thread using ThreadLocal
If you're interested, I might knock up an example later

Here is a simple PeriodicNonOverlappingTimer class, that provides just the requested features, and nothing more than that. This timer cannot be started and stopped on demand, and neither can have its interval changed. It just invokes the specified action periodically in a non overlapping manner, until the timer is disposed.
/// <summary>
/// Invokes an action on the ThreadPool at specified intervals, ensuring
/// that the invocations will not overlap, until the timer is disposed.
/// </summary>
public class PeriodicNonOverlappingTimer : IDisposable, IAsyncDisposable
{
private readonly System.Threading.Timer _timer;
public PeriodicNonOverlappingTimer(Action periodicAction,
TimeSpan dueTime, TimeSpan period)
{
// Arguments validation omitted
_timer = new(_ =>
{
var stopwatch = Stopwatch.StartNew();
periodicAction();
var nextDueTime = period - stopwatch.Elapsed;
if (nextDueTime < TimeSpan.Zero) nextDueTime = TimeSpan.Zero;
try { _timer.Change(nextDueTime, Timeout.InfiniteTimeSpan); }
catch (ObjectDisposedException) { } // Ignore this exception
});
_timer.Change(dueTime, Timeout.InfiniteTimeSpan);
}
public void Dispose() => _timer.DisposeAsync().AsTask().Wait();
public ValueTask DisposeAsync() => _timer.DisposeAsync();
}
Usage example. Shows how to create a non-overlapping timer that starts immediately, with a period of 10 seconds.
var timer = new PeriodicNonOverlappingTimer(() =>
{
DoSomethingCool();
}, TimeSpan.Zero, TimeSpan.FromSeconds(10));
//...
timer.Dispose(); // Stop the timer once and for all
In case the DoSomethingCool fails, the exception will be thrown on the ThreadPool, causing the process to crash. So you may want to add a try/catch block, and handle all the exceptions that may occur.
The Dispose is a potentially blocking method. If the periodicAction is currently running, the Dispose will block until the last invocation is completed.
If you don't want to wait for this to happen, you can do this instead:
_ = timer.DisposeAsync(); // Stop the timer without waiting it to finish

How to raise only 1 Timer event in C#?

How do I get a timer event to fire one at a time.
For example I have a timer that raises an event every 10 minutes.
The event that is raised takes 10 or more minutes to finish executing.
I would like the timer to reset AFTER the event has finished.
In other words I do not want to raise more than 1 instance of the event at any one time.

Use System.Timers.Timer not the Threading one
Set AutoReset to false.
Then Start it again when you're done.

Usually what I do is have my event stop the timer when it's raised and then restart the timer when the event process completes:
private void timerHandler(object sender, TimerElapsedEventArgs e)
{
Timer timer = (Timer)sender;
timer.Stop();
RunProcess();
timer.Start();
}
public void RunProcess()
{
/* Do stuff that takes longer than my timer interval */
}
Now my timer will start again on completion of the process

It may be difficult to stop timers for efficiency or logic. The following code synchronizes skipping the events.
static readonly object key = new object();
void TimerHandler(object sender, TimerElapsedEventArgs e)
{
if(Monitor.TryEnter(key))
{
try
{
//do your stuff
}
finally
{
Montitor.Exit(key);
}
}
}

How to have a loop in a Windows service without using the Timer

I want to call a Business layer method from a Windows service (done using C# and .NET) after every 10 seconds. However, i dont want to use the Timer_Elapsed event since it starts up another thread/process if the first thread/process is still running. I just need a single threaded approach, since multiple calls to the same Business method creates unwanted complications.
So i added a do--while loop in the on_start. I know this is not the correct way since it spawns this process which becomes an orphan if the service is shut down.
How can i approach this problem ?
Regards,
Chak

There's another way to get timed execution, the WaitHandle.WaitOne() method provides a timeout argument. That works very nicely in a service as it lets you implement the need to stop the service and periodic execution in a single method call. The template looks like this:
Thread Worker;
AutoResetEvent StopRequest = new AutoResetEvent(false);
protected override void OnStart(string[] args) {
// Start the worker thread
Worker = new Thread(DoWork);
Worker.Start();
}
protected override void OnStop() {
// Signal worker to stop and wait until it does
StopRequest.Set();
Worker.Join();
}
private void DoWork(object arg) {
// Worker thread loop
for (;;) {
// Run this code once every 10 seconds or stop right away if the service
// is stopped
if (StopRequest.WaitOne(10000)) return;
// Do work...
//...
}
}

Use a timer, but as soon as you enter the Timer handler method, disable the timer so that no more events are raised. Just before exiting the handler, re-enable the timer.

Check out this discussion, and in particular the answer by jsw. It suggests a synchronization mechanism to prevent multiple simultaneous calls to the business logic. Just disabling the timer in the Elapsed handler method isn't guaranteed to prevent parallel calls since the handler is invoked on a separate thread. Use a lock as jsw suggests, and stop the timer within the synchronized code block.
Alternatively, you could use a Timer and set the AutoReset property to false. That way, the Elapsed event is raised only once and you can reset the timer manually towards the end of the handler method.

while(true)
{
..do something
Thread.sleep( some time or day);
}

Thread thread;
private void DoWork(object arg)
{
while (true)
{
// Run this code once every 20 seconds or stop if the service is stopped
try
{
Thread.Sleep(20000);
//Do work....
}
catch(ThreadInterruptedException)
{
return;
}
}
}
protected override void OnStart(string[] args)
{
// Start the thread
thread = new Thread(DoWork);
mWorker.Start();
}
protected override void OnStop()
{
// interrupt thread and wait until it does
thread.Interrupt();
thread.Join();
}

Best Timer for using in a Windows service

Locked. This question and its answers are locked because the question is off-topic but has historical significance. It is not currently accepting new answers or interactions.
I need to create some windows service which will execute every N period of time.
The question is:
Which timer control should I use: System.Timers.Timer or System.Threading.Timer one? Does it influence on something?
I am asking because I heard many evidences to non correct work of System.Timers.Timer in windows services.
Thank you.

Both System.Timers.Timer and System.Threading.Timer will work for services.
The timers you want to avoid are System.Web.UI.Timer and System.Windows.Forms.Timer, which are respectively for ASP applications and WinForms. Using those will cause the service to load an additional assembly which is not really needed for the type of application you are building.
Use System.Timers.Timer like the following example (also, make sure that you use a class level variable to prevent garbage collection, as stated in Tim Robinson's answer):
using System;
using System.Timers;
public class Timer1
{
private static System.Timers.Timer aTimer;
public static void Main()
{
// Normally, the timer is declared at the class level,
// so that it stays in scope as long as it is needed.
// If the timer is declared in a long-running method,
// KeepAlive must be used to prevent the JIT compiler
// from allowing aggressive garbage collection to occur
// before the method ends. (See end of method.)
//System.Timers.Timer aTimer;
// Create a timer with a ten second interval.
aTimer = new System.Timers.Timer(10000);
// Hook up the Elapsed event for the timer.
aTimer.Elapsed += new ElapsedEventHandler(OnTimedEvent);
// Set the Interval to 2 seconds (2000 milliseconds).
aTimer.Interval = 2000;
aTimer.Enabled = true;
Console.WriteLine("Press the Enter key to exit the program.");
Console.ReadLine();
// If the timer is declared in a long-running method, use
// KeepAlive to prevent garbage collection from occurring
// before the method ends.
//GC.KeepAlive(aTimer);
}
// Specify what you want to happen when the Elapsed event is
// raised.
private static void OnTimedEvent(object source, ElapsedEventArgs e)
{
Console.WriteLine("The Elapsed event was raised at {0}", e.SignalTime);
}
}
/* This code example produces output similar to the following:
Press the Enter key to exit the program.
The Elapsed event was raised at 5/20/2007 8:42:27 PM
The Elapsed event was raised at 5/20/2007 8:42:29 PM
The Elapsed event was raised at 5/20/2007 8:42:31 PM
...
*/
If you choose System.Threading.Timer, you can use as follows:
using System;
using System.Threading;
class TimerExample
{
static void Main()
{
AutoResetEvent autoEvent = new AutoResetEvent(false);
StatusChecker statusChecker = new StatusChecker(10);
// Create the delegate that invokes methods for the timer.
TimerCallback timerDelegate =
new TimerCallback(statusChecker.CheckStatus);
// Create a timer that signals the delegate to invoke
// CheckStatus after one second, and every 1/4 second
// thereafter.
Console.WriteLine("{0} Creating timer.\n",
DateTime.Now.ToString("h:mm:ss.fff"));
Timer stateTimer =
new Timer(timerDelegate, autoEvent, 1000, 250);
// When autoEvent signals, change the period to every
// 1/2 second.
autoEvent.WaitOne(5000, false);
stateTimer.Change(0, 500);
Console.WriteLine("\nChanging period.\n");
// When autoEvent signals the second time, dispose of
// the timer.
autoEvent.WaitOne(5000, false);
stateTimer.Dispose();
Console.WriteLine("\nDestroying timer.");
}
}
class StatusChecker
{
int invokeCount, maxCount;
public StatusChecker(int count)
{
invokeCount = 0;
maxCount = count;
}
// This method is called by the timer delegate.
public void CheckStatus(Object stateInfo)
{
AutoResetEvent autoEvent = (AutoResetEvent)stateInfo;
Console.WriteLine("{0} Checking status {1,2}.",
DateTime.Now.ToString("h:mm:ss.fff"),
(++invokeCount).ToString());
if(invokeCount == maxCount)
{
// Reset the counter and signal Main.
invokeCount = 0;
autoEvent.Set();
}
}
}
Both examples comes from the MSDN pages.

Don't use a service for this. Create a normal application and create a scheduled task to run it.
This is the commonly held best practice. Jon Galloway agrees with me. Or maybe its the other way around. Either way, the fact is that it is not best practices to create a windows service to perform an intermittent task run off a timer.
"If you're writing a Windows Service that runs a timer, you should re-evaluate your solution."
–Jon Galloway, ASP.NET MVC community program manager, author, part time superhero

Either one should work OK. In fact, System.Threading.Timer uses System.Timers.Timer internally.
Having said that, it's easy to misuse System.Timers.Timer. If you don't store the Timer object in a variable somewhere, then it is liable to be garbage collected. If that happens, your timer will no longer fire. Call the Dispose method to stop the timer, or use the System.Threading.Timer class, which is a slightly nicer wrapper.
What problems have you seen so far?

I agree with previous comment that might be best to consider a different approach. My suggest would be write a console application and use the windows scheduler:
This will:
Reduce plumbing code that replicates scheduler behaviour
Provide greater flexibility in terms
of scheduling behaviour (e.g. only
run on weekends) with all scheduling logic abstracted from application code
Utilise the command line arguments
for parameters without having to
setup configuration values in config
files etc
Far easier to debug/test during development
Allow a support user to execute by invoking
the console application directly
(e.g. useful during support
situations)

As already stated both System.Threading.Timer and System.Timers.Timer will work. The big difference between the two is that System.Threading.Timer is a wrapper arround the other one.
System.Threading.Timer will have more exception handling while
System.Timers.Timer will swallow all the exceptions.
This gave me big problems in the past so I would always use 'System.Threading.Timer' and still handle your exceptions very well.

I know this thread is a little old but it came in handy for a specific scenario I had and I thought it worth while to note that there is another reason why System.Threading.Timer might be a good approach.
When you have to periodically execute a Job that might take a long time and you want to ensure that the entire waiting period is used between jobs or if you don't want the job to run again before the previous job has finished in the case where the job takes longer than the timer period.
You could use the following:
using System;
using System.ServiceProcess;
using System.Threading;
public partial class TimerExampleService : ServiceBase
{
private AutoResetEvent AutoEventInstance { get; set; }
private StatusChecker StatusCheckerInstance { get; set; }
private Timer StateTimer { get; set; }
public int TimerInterval { get; set; }
public CaseIndexingService()
{
InitializeComponent();
TimerInterval = 300000;
}
protected override void OnStart(string[] args)
{
AutoEventInstance = new AutoResetEvent(false);
StatusCheckerInstance = new StatusChecker();
// Create the delegate that invokes methods for the timer.
TimerCallback timerDelegate =
new TimerCallback(StatusCheckerInstance.CheckStatus);
// Create a timer that signals the delegate to invoke
// 1.CheckStatus immediately,
// 2.Wait until the job is finished,
// 3.then wait 5 minutes before executing again.
// 4.Repeat from point 2.
Console.WriteLine("{0} Creating timer.\n",
DateTime.Now.ToString("h:mm:ss.fff"));
//Start Immediately but don't run again.
StateTimer = new Timer(timerDelegate, AutoEventInstance, 0, Timeout.Infinite);
while (StateTimer != null)
{
//Wait until the job is done
AutoEventInstance.WaitOne();
//Wait for 5 minutes before starting the job again.
StateTimer.Change(TimerInterval, Timeout.Infinite);
}
//If the Job somehow takes longer than 5 minutes to complete then it wont matter because we will always wait another 5 minutes before running again.
}
protected override void OnStop()
{
StateTimer.Dispose();
}
}
class StatusChecker
{
public StatusChecker()
{
}
// This method is called by the timer delegate.
public void CheckStatus(Object stateInfo)
{
AutoResetEvent autoEvent = (AutoResetEvent)stateInfo;
Console.WriteLine("{0} Start Checking status.",
DateTime.Now.ToString("h:mm:ss.fff"));
//This job takes time to run. For example purposes, I put a delay in here.
int milliseconds = 5000;
Thread.Sleep(milliseconds);
//Job is now done running and the timer can now be reset to wait for the next interval
Console.WriteLine("{0} Done Checking status.",
DateTime.Now.ToString("h:mm:ss.fff"));
autoEvent.Set();
}
}