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c# Null Value Exception inside lock live data collection/aggregation

Lets suppose I have a single class that has two methods OnBarEvent & Update.
Update: subscribes to a continuous stream of data that comes in asynchronously.
OnBarEvent: will send an event out every n minutes. I am using a timer class to keep track of time and then just have SendEvent attached to the timer class event handler. Essentially, this method will be called whenever N minutes pass
The program will receive asynchronous data via OnEvent which will just summarize the data over a period of time. Once a specified time has passed, then the SendEvent will be called
namespace Common.Aggregator
{
public class BaseTimeAggregator
{
//The last time we emitted a consolidated bar
private DateTime? _lastEmit;
//The minimum timespan between creating new bars.
private readonly TimeSpan? _period;
//The working bar used for aggregating the data
private Bar _workingBar;
//The last working bar
private Bar l_workingBar;
//The Start Time
private DateTime StartTime;
private System.Timers.Timer timer;
public new event EventHandler<Bar> DataConsolidated;
private void OnBarEvent(Object source, System.Timers.ElapsedEventArgs e)
{
if (DateTime.Now > StartTime)
{
if (_workingBar != null)
{
//Console.WriteLine("New Bar: {0}", e.SignalTime);
lock (_workingBar)
{
// Fire Bar
var workingTradeBar = _workingBar as Bar;
if(l_workingBar == null)
{
decimal close_ret = workingTradeBar.Close / workingTradeBar.PreClosePrice;
workingTradeBar.Logret = (decimal)Math.Log((double)close_ret);
}
else
{
// PROBLEM: workingTradeBar can be null here for some reason
decimal value = workingTradeBar.Close / l_workingBar.Close;
workingTradeBar.Logret = (decimal) Math.Log((double)value);
}
l_workingBar = workingTradeBar;
DataConsolidated(this, workingTradeBar);
_workingBar = null;
}
}
}
}
public void Update(Tick data)
{
AggregateBar(data);
}
protected void AggregateBar(Tick data)
{
// Create New Bar
if (_workingBar == null)
{
_workingBar = new Bar(data.LastPrice, data.LastPrice, data.LastPrice, data.LastPrice);
_workingBar.PreClosePrice = data.PreClosePrice;
}
lock (_workingBar)
{
// In the case it got accessed in between
if (_workingBar == null)
{
_workingBar = new Bar(data.LastPrice, data.LastPrice, data.LastPrice, data.LastPrice);
_workingBar.PreClosePrice = data.PreClosePrice;
}
// Update Bar
_workingBar.Update(data.DataType, data.LastPrice, data.BidPrice, data.AskPrice,
data.Volume, data.BidSize, data.AskSize);
}
}
return new DateTime(
dateTime.Year,
dateTime.Month,
dateTime.Day,
hours,
minutes,
seconds,
milliseconds,
dateTime.Kind);
}
}
}
The problem I am running in to is that within the lock, when I access the workingTradeBar variable (see commented code above where "PROBLEM"), there are situations where its null and throws a system.null error. I can't figure out how it can be null given I made a check right before I entered the lock. Also, the only place I set it null is in the same method since I want to start summarizing the data after N minutes passed.
Thanks
This is different from the other question because its purely a multi-threading problem/race condition.

Some remarks:
Event handlers should get the current instance from input params, not from the local variable.
If required need store references to all Bars.
Any method that manipulates the Bars should be synchronized.
As alternative the lock-statement can be used ReaderWriterLockSlim.
namespace Common.Aggregator
{
public class BaseTimeAggregator
{
// REMOVE this field
// --> private Bar _workingBar;
private readonly object _lock = new object();
private readonly Dictionary<int, Bar> _barDictionary = new Dictionary<int, Bar>();
private void OnBarEvent(Object source, System.Timers.ElapsedEventArgs e)
{
var bar = (Bar)source;
// Manipulate with the actual instance defined in 'bar'-variable ..
}
public void Update(Tick data)
{
lock (_lock) {
AggregateBar(data);
}
}
public void Smth_method(int barId)
{
lock (_lock) {
var bar = _barDictionary[uniqueBarId];
// ..
}
}
protected void AggregateBar(Tick data)
{
var uniqueBarId = data.{some param that identify bar};
if (_barDictionary.ContainsKey(uniqueBarId)) {
_barDictionary[uniqueBarId].Update(data.DataType, data.LastPrice, data.BidPrice, data.AskPrice, data.Volume, data.BidSize, data.AskSize);
return;
}
var bar = new Bar(data.LastPrice, data.LastPrice, data.LastPrice, data.LastPrice);
bar.PreClosePrice = data.PreClosePrice;
_barDictionary[uniqueBarId] = bar;
}
}
}

Execute method delayed and only once even if triggered twice within the delay

I have the case, that I have two properties which both have change notification via INotifyPropertyChanged and trigger a reconfiguration of my attached hardware, which takes some time and can't be executed twice in parallel.
Now there is one situation where both of these properties are changed "at the same time" and would trigger two reconfigurations after another.
To avoid that I would like to implement some kind of a delay before executing the reconfiguration and "ignore" the second call if one is already pending.
Is there some common pattern or logic available to solve something like this?
At the moment I use something like the following:
public class ExecutionManager
{
private readonly object reconfigurationLock = new object();
private bool reconfigurationScheduled;
/// <summary>Reconfigures the measurement.</summary>
public void ReconfigureMeasurement()
{
//slow/long method
}
/// <summary>Reconfigures the measurement delayed so two calls short after each other only trigger one reconfiguration.</summary>
public void ReconfigureMeasurementDelayed()
{
lock (reconfigurationLock)
{
if (reconfigurationScheduled)
return;
reconfigurationScheduled = true;
}
Task.Run(async () =>
{
await Task.Delay(50).ConfigureAwait(false);
ReconfigureMeasurement();
reconfigurationScheduled = false;
});
}
}
...but this seems a little bit "hacky" to me and I have the feeling there is a way better solution to my problem.
One thing which is important to keep in mind:
I can NOT call ReconfigureMeasurement before the second change event also "happened" as this would cause that the changed value of that one is lost, as the new values are sent to the hardware directly at the beginning of ReconfigureMeasurement and so before the second parameter changed if I have no delay.

I think you can just do:
/// <summary>Reconfigures the measurement delayed so two calls short after each other only trigger one reconfiguration.</summary>
public void ReconfigureMeasurementDelayed()
{
lock (reconfigurationLock)
{
if (reconfigurationScheduled)
return;
reconfigurationScheduled = true;
}
Task.Run(() =>
{
ReconfigureMeasurement();
lock (reconfigurationLock) {
reconfigurationScheduled = false;
}
});
}
And no need for any delays, they are not solving problem anyway.

There is an inherent weakness in the INotifyPropertyChanged architecture in that it allows a client to observe a model in an inconsistent state. Consider the example below. Notice how a subscriber will receive a notification about the value X changing followed by a notification about the value XSquared changing. If the client was something like a UI where when X changes it goes back and looks only at X and then later when XSquared changes it goes back and looks only a XSquared then the problem doesn't manifest. But when you are dealing with a condition where you need to look at other parts of the model beyond what is immediately being notified then you run the risk of seeing an invalid state.
class ViewModel : INotifyPropertyChanged
{
public int X
{
get { return _x; }
set
{
_x = value;
_xSquared = _a * _a;
NotifyPropertyChanged("X");
NotifyPropertyChanged("XSquared");
}
}
public int XSquared { get { return _xSquared; }
}
Having worked with these types of systems for a long time I have found that it is best to allow a change and any of its side effects to completely settle and then send a single notification that something changed. e.g.
class ViewModel
{
public event EventHandler SomethingChanged;
public int X
{
get { return _x; }
set
{
_x = value;
_xSquared = _a * _a;
SomethingChanged(this, EventArgs.Empty);
}
}
public int XSquared { get { return _xSquared; }
}
public class ExecutionManager
{
private ViewModel _viewModel;
public void OnSomethingChanged(...)
{
// state is now consistent so long as everything is
// single threaded.
ReconfigureHardware(_viewModel.X, _viewModel.XSquared);
}
}

At the moment I use the following solution thanks to Arons comment:
public class ExecutionManager
{
private readonly int reconfigurationDelay = 50;
private IObservable<EventArgs> delayedReconfigurations;
/// <summary>Occurs when a reconfiguration is required.</summary>
public event EventHandler ReconfigurationRequired;
/// <summary>Called when a reconfiguration is required.</summary>
public void OnReconfigurationRequired() => ReconfigurationRequired.Raise(this);
/// <summary>Initializes the manager.</summary>
public override void Init()
{
base.Init();
delayedReconfigurations = Observable.FromEvent<EventHandler, EventArgs>(
h => (s, e) => h(e),
h => ReconfigurationRequired += h,
h => ReconfigurationRequired -= h);
delayedReconfigurations.Throttle(TimeSpan.FromMilliseconds(reconfigurationDelay))
.Subscribe(e => ReconfigureMeasurement());
}
/// <summary>Reconfigures the measurement.</summary>
public void ReconfigureMeasurement()
{
//long/slow method
}
}

Subscribing to an event of a class that holds the override method of the class you reference

I am working with background workers to update a progress bar in a WPF UI I am working on. This background worker is getting its progress updates from multiple events that I am subscribed to, because the progress bar goes through several loading stages, and the percentages for those come from several places. here is some example/pseudo code explaining what I mean
The DoWork method of my background worker and the methods I am using to currently get some progress updates
// These are working fine
private void BwOnDoWork(object sender, DoWorkEventArgs doWorkEventArgs)
{
orderProcessing.OnOrderProgress += OrderStatus;
orderProcessing.OnStandardOrderProgress += StandardOrderStatus;
orderProcessing.CreateOrders(orders);
}
private void OrderStatus(int currentCount, int totalItems, string Message)
{
if (totalItems > 0)
bw.ReportProgress(Convert.ToInt32(((double)currentCount / (double)totalItems) * 100),
Message);
}
private void StandardOrderStatus(int currentCount, int totalItems, string Message)
{
if (totalItems > 0)
bw.ReportProgress(Convert.ToInt32(((double)currentCount / (double)totalItems) * 100),
Message);
}
Some code from my order processing class
public abstract class OrderProcessing
{
public delegate void OrderProgress(int CurrentItems, int TotalItems, string Message);
public event MasterSalesOrder.StandardOrderProgress OnStandardOrderProgress;
public event OrderProgress OnOrderProgress;
public abstract List<MasterSalesOrder> CreateOrders(List<Order> orders);
}
Some code from the class that holds the override method for CreateOrders()
public abstract class OrderProcessingFile : OrderProcessing
{
public event OrderProgress OnOrderProgress;
public override List<MasterSalesOrder> CreateOrders(List<Order> orders)
{
//Does Some Stuff
foreach(var stuff in stuffs)
{
OnOrderProgress(currentCount, totalCount, "Message");
}
}
}
Since I am clearly not explaining this well, I need to get info from the OrderProcessingFiles OnOrderProgress event via the OrderProcessing class that I create in the DoWork method.I am unsure on how to subscribe to an event when my code never directly instantiates an instance of the OrderProcessingFile class and it is never directly referred to.
I have tried looking for answers but as my title will show I am having a hard time even wording this in a way to get useful results, and I am genuinely stuck on this one. Let me know if more detail is needed, I tried to strip down my code to only the relevant parts but I feel like I'm explaining this strangely.

I would recommend that you create a thread safe singleton progress manager. Then have each of the background workers contact it with updates. The progress manager will use a DispatcherTimer (which runs on the GUI thread) to update the GUI appropriately.
Raw example:
public static class StatusReportManager
{
// Standard singleton code to create the manager and access it.
// Start/create the dispatch time as well.
private static DispatcherTimer Timer { get; set; }
private static object _syncObject = new object();
public static void ReportStatus(...)
{
lock (_syncObject)
{
// Process any states and set instance properties for reading
// by the timer operation.
}
}
private void ShowStatus() // Used by the dispatch timer
{
lock (_syncObject)
{
// Do any updates to the GUI in here from current state.
}
}
}

I have realized what it is I was really trying to do and have thus found an answer. Using the method found in this MSDN article I have implemented the follow code:
This is my UI
private void BwOnDoWork(object sender, DoWorkEventArgs doWorkEventArgs)
{
orderProcessing.OnOrderProgress += OrderStatus;
orderProcessing.CreateOrders(FanGlobal.BrandItems, FanGlobal.BrandItemMasterCustomers);
}
private void OrderStatus(object obj, OrderProcessing.OrderProgressEventArgs e)
{
if (e.totalCount > 0)
bw.ReportProgress(Convert.ToInt32(((double)e.currentCount / (double)e.totalCount) * 100),e.message);
}
This in my OrderProcessing class
public event EventHandler<OrderProgressEventArgs> OnOrderProgress;
public class OrderProgressEventArgs : EventArgs
{
public int currentCount;
public int totalCount;
public string message;
public OrderProgressEventArgs(int c, int t, string m)
{
currentCount = c;
totalCount = t;
message = m;
}
}
protected virtual void OnOrderProgressChanged(OrderProgressEventArgs e)
{
EventHandler<OrderProgressEventArgs> handler = OnOrderProgress;
if (handler != null)
{
handler(this, e);
}
}
public abstract List<MasterSalesOrder> CreateOrders(List<BrandItem> BrandItems = null, List<BrandItemMasterCustomer> BrandItemMasterCustomers = null);
and then I can use it in my child class OrderProcessingFile like so
public override List<MasterSalesOrder> CreateOrders(List<BrandItem> BrandItems = null, List<BrandItemMasterCustomer> BrandItemMasterCustomers = null)
{
//Do some Stuff
OnOrderProgressChanged(new OrderProgressEventArgs(count, totalItems, "Extracting"));
}
and everything is working like a charm. Sorry for the utterly confusing question and the apparent huge gap of knowledge I have/had, but hopefully this will help someone else in the future.

Using a thread to continuously check for changes to a value

I am trying to create a thread which will continuously check for changes to a value, then visually show that change in a PictureBox located in my GUI.
What I actually wrote is a bit more complicated, so I simplified it while keeping the basic idea, I would be happy to provide clarification if this isn't enough:
public class CheckPictures
{
PictureBox update;
List<String> check;
public CheckPictures(PictureBox anUpdate, List<String> aCheck)
{
update = anUpdate;
check = aCheck;
}
public void start()
{
while(true)
{
if (aCheck[0] == "Me")
{
update.Image = Image.fromFile("");
}
}
}
}
static int Main(string[] args)
{
List<String> picturesList = new List<String>();
CheckPictures thread1 = new CheckPictures(PictureBox1, picturesList);
Thread oThread1 = new Thread(thread1.start));
}
What I want it to do is dynamically change the picture in PictureBox1 if I were to add the string "Me" to pictureList. The above code isn't working like I'd hoped. I had thought that by passing the actual PictureBox and List, any changes to the List elsewhere is the program would be caught by the thread. So my first question is: Is this possible? And if so, what change would I need to make to my code to achieve it?

You might want to use events. You register an eventhandler and when something changes in one thread it calls an event handler in the other to do the work. Busy waiting wastes cpu.

You definetely do not want to do an infinite loop, this will just consume cpu:
while(true)
{
if (aCheck[0] == "Me")
{
update.Image = Image.fromFile("");
}
}
I think you should look into the CountdownLatch class.
public class CountdownLatch
{
private int m_remain;
private EventWaitHandle m_event;
public CountdownLatch(int count)
{
m_remain = count;
m_event = new ManualResetEvent(false);
}
public void Signal()
{
// The last thread to signal also sets the event.
if (Interlocked.Decrement(ref m_remain) == 0)
m_event.Set();
}
public void Wait()
{
m_event.WaitOne();
}
}
The basic idea here is that you need to stop execution on your thread for some time and resume whenever a certain condition has been met (perhaps on another thread).
In other words, you will have a counter, decrement its value on certain condition and whenever it goes to zero you fire your event, execute some code and then start over (stop execution and wait for the counter to go to zero).
In your case you could set the counter to 1 and decrement its value whenever you've set aCheck[0] = "Me"; This way you don't waste CPU.
Pseudo code:
Initialize counter:
CountdownLatch latch = new CountdownLatch(1);
Make thread wait:
public void start()
{
while(true)
{
latch.Wait(); //execution stops
{
//execution resumes once the latch counter is zero.
if (aCheck[0] == "Me") //double check you have what you need
{
update.Image = Image.fromFile("");
latch = new CountdownLatch(1); //reset if you need to do it again
}
}
}
}
Whenever your condition is met (i.e. aCheck[0] = "Me";) signal your latch:
latch.Signal();
this last line will make the thread resume execution. Good stuff.

Create some object, which will raise event, when new picture was added. E.g. class representing pictures collection:
public class PicturesCollection
{
public event EventHandler<PictureAddedEventArgs> PictureAdded;
private List<string> _pictures = new List<string>();
public void Add(string name)
{
_pictures.Add(name);
if (PictureAdded != null)
PictureAdded(this, new PictureAddedEventArgs(name));
}
public IEnumerable<string> Pictures
{
get { return _pictures; }
}
}
If you want to provide some additional data to event, create custom EventArgs:
public class PictureAddedEventArgs : EventArgs
{
public PictureAddedEventArgs(string name)
{
Name = name;
}
public string Name { get; private set; }
}
All you need now - create pictures collection and subscribe to that event:
static int Main(string[] args)
{
PicturesCollection pictures = new PicturesCollection();
pictures.PictureAdded += Pictures_PictureAdded;
}
static void Pictures_PictureAdded(object sender, PictureAddedEventArgs e)
{
if (e.Name == "Me")
PictureBox1.Image = Image.fromFile("");
}
If you add somewhere in your application new picture to collection, it will raise PictureAdded event, which you can handle and update PictureBox. CPU is not wasted in this case.

Alarm clock application in .Net

I'm not really writing an alarm clock application, but it will help to illustrate my question.
Let's say that I have a method in my application, and I want this method to be called every hour on the hour (e.g. at 7:00 PM, 8:00 PM, 9:00 PM etc.). I could create a Timer and set its Interval to 3600000, but eventually this would drift out of sync with the system clock. Or I could use a while() loop with Thread.Sleep(n) to periodically check the system time and call the method when the desired time is reached, but I don't like this either (Thread.Sleep(n) is a big code smell for me).
What I'm looking for is some method in .Net that lets me pass in a future DateTime object and a method delegate or event handler, but I haven't been able to find any such thing. I suspect there's a method in the Win32 API that does this, but I haven't been able to find that, either.

Or, you could create a timer with an interval of 1 second and check the current time every second until the event time is reached, if so, you raise your event.
You can make a simple wrapper for that :
public class AlarmClock
{
public AlarmClock(DateTime alarmTime)
{
this.alarmTime = alarmTime;
timer = new Timer();
timer.Elapsed += timer_Elapsed;
timer.Interval = 1000;
timer.Start();
enabled = true;
}
void timer_Elapsed(object sender, ElapsedEventArgs e)
{
if(enabled && DateTime.Now > alarmTime)
{
enabled = false;
OnAlarm();
timer.Stop();
}
}
protected virtual void OnAlarm()
{
if(alarmEvent != null)
alarmEvent(this, EventArgs.Empty);
}
public event EventHandler Alarm
{
add { alarmEvent += value; }
remove { alarmEvent -= value; }
}
private EventHandler alarmEvent;
private Timer timer;
private DateTime alarmTime;
private bool enabled;
}
Usage:
AlarmClock clock = new AlarmClock(someFutureTime);
clock.Alarm += (sender, e) => MessageBox.Show("Wake up!");
Please note the code above is very sketchy and not thread safe.

Interesting, I've actually come across a very similar issue and went looking for a method in the .Net framework that would handle this scenario. In the end, we ended up implementing our own solution that was a variation on a while loop w/ Thread.Sleep(n) where n gets smaller the closer you get to the desired target time (logarithmically actually, but with some reasonable thresholds so you're not maxing the cpu when you get close to the target time.) Here's a really simple implementation that just sleeps half the time between now and the target time.
class Program
{
static void Main(string[] args)
{
SleepToTarget Temp = new SleepToTarget(DateTime.Now.AddSeconds(30),Done);
Temp.Start();
Console.ReadLine();
}
static void Done()
{
Console.WriteLine("Done");
}
}
class SleepToTarget
{
private DateTime TargetTime;
private Action MyAction;
private const int MinSleepMilliseconds = 250;
public SleepToTarget(DateTime TargetTime,Action MyAction)
{
this.TargetTime = TargetTime;
this.MyAction = MyAction;
}
public void Start()
{
new Thread(new ThreadStart(ProcessTimer)).Start();
}
private void ProcessTimer()
{
DateTime Now = DateTime.Now;
while (Now < TargetTime)
{
int SleepMilliseconds = (int) Math.Round((TargetTime - Now).TotalMilliseconds / 2);
Console.WriteLine(SleepMilliseconds);
Thread.Sleep(SleepMilliseconds > MinSleepMilliseconds ? SleepMilliseconds : MinSleepMilliseconds);
Now = DateTime.Now;
}
MyAction();
}
}

You could simply reset the timer duration each time it fires, like this:
// using System.Timers;
private void myMethod()
{
var timer = new Timer {
AutoReset = false, Interval = getMillisecondsToNextAlarm() };
timer.Elapsed += (src, args) =>
{
// Do timer handling here.
timer.Interval = getMillisecondsToNextAlarm();
timer.Start();
};
timer.Start();
}
private double getMillisecondsToNextAlarm()
{
// This is an example of making the alarm go off at every "o'clock"
var now = DateTime.Now;
var inOneHour = now.AddHours(1.0);
var roundedNextHour = new DateTime(
inOneHour.Year, inOneHour.Month, inOneHour.Day, inOneHour.Hour, 0, 0);
return (roundedNextHour - now).TotalMilliseconds;
}

You could create an Alarm class which has a dedicated thread which goes to sleep until the specified time, but this will use the Thread.Sleep method. Something like:
/// <summary>
/// Alarm Class
/// </summary>
public class Alarm
{
private TimeSpan wakeupTime;
public Alarm(TimeSpan WakeUpTime)
{
this.wakeupTime = WakeUpTime;
System.Threading.Thread t = new System.Threading.Thread(TimerThread) { IsBackground = true, Name = "Alarm" };
t.Start();
}
/// <summary>
/// Alarm Event
/// </summary>
public event EventHandler AlarmEvent = delegate { };
private void TimerThread()
{
DateTime nextWakeUp = DateTime.Today + wakeupTime;
if (nextWakeUp < DateTime.Now) nextWakeUp = nextWakeUp.AddDays(1.0);
while (true)
{
TimeSpan ts = nextWakeUp.Subtract(DateTime.Now);
System.Threading.Thread.Sleep((int)ts.TotalMilliseconds);
try { AlarmEvent(this, EventArgs.Empty); }
catch { }
nextWakeUp = nextWakeUp.AddDays(1.0);
}
}
}

I know it's a bit of an old question, but I came across this when I was looking for an answer to something else. I thought I'd throw my two cents in here, since I recently had this particular issue.
Another thing you can do is schedule the method like so:
/// Schedule the given action for the given time.
public async void ScheduleAction ( Action action , DateTime ExecutionTime )
{
try
{
await Task.Delay ( ( int ) ExecutionTime.Subtract ( DateTime.Now ).TotalMilliseconds );
action ( );
}
catch ( Exception )
{
// Something went wrong
}
}
Bearing in mind it can only wait up to the maximum value of int 32 (somewhere around a month), it should work for your purposes. Usage:
void MethodToRun ( )
{
Console.WriteLine ("Hello, World!");
}
void CallingMethod ( )
{
var NextRunTime = DateTime.Now.AddHours(1);
ScheduleAction ( MethodToRun, NextRunTime );
}
And you should have a console message in an hour.

What about System.Timers.Timer class ? See http://msdn.microsoft.com/en-us/library/system.timers.timer.aspx

I have used this before with great success:
Vb.net:
Imports System.Threading
Public Class AlarmClock
Public startTime As Integer = TimeOfDay.Hour
Public interval As Integer = 1
Public Event SoundAlarm()
Public Sub CheckTime()
While TimeOfDay.Hour < startTime + interval
Application.DoEvents()
End While
RaiseEvent SoundAlarm()
End Sub
Public Sub StartClock()
Dim clockthread As Thread = New Thread(AddressOf CheckTime)
clockthread.Start()
End Sub
End Class
C#:
using System.Threading;
public class AlarmClock
{
public int startTime = TimeOfDay.Hour;
public int interval = 1;
public event SoundAlarmEventHandler SoundAlarm;
public delegate void SoundAlarmEventHandler();
public void CheckTime()
{
while (TimeOfDay.Hour < startTime + interval) {
Application.DoEvents();
}
if (SoundAlarm != null) {
SoundAlarm();
}
}
public void StartClock()
{
Thread clockthread = new Thread(CheckTime);
clockthread.Start();
}
}
I don't know if the c# works, but the vb works just fine.
Usage in VB:
Dim clock As New AlarmClock
clock.interval = 1 'Interval is in hours, could easily convert to anything else
clock.StartClock()
Then, just add an event handler for the SoundAlarm event.