Chapter110:Timers

Section110.1:MultithreadedTimers
System.Threading.Timer-Simplestmultithreadedtimer.Containstwomethodsandoneconstructor.

Example: A timer calls the DataWrite method, which writes “multithread executed…” after five seconds have elapsed, and then every second after that until the user presses Enter:

usingSystem;

usingSystem.Threading;

classProgram

{

staticvoidMain()

{

//Firstinterval=5000ms;subsequentintervals=1000ms

Timertimer=newTimer(DataWrite,”multithreadexecuted…”,5000,1000); Console.ReadLine();

timer.Dispose();//Thisbothstopsthetimerandcleansup.

}

staticvoidDataWrite(objectdata)

{

//Thisrunsonapooledthread

Console.WriteLine(data);//Writes”multithreadexecuted…”

}

}

Note:Willpostaseparatesectionfordisposingmultithreadedtimers.

Change-Thismethodcanbecalledwhenyouwouldlikechangethetimerinterval.

Timeout.Infinite- If youwant to firejust once. Specifythis in thelast argument of theconstructor.

System.Timers-Anothertimerclassprovidedby.NETFramework.ItwrapstheSystem.Threading.Timer.

Features:

• IComponent- Allowing it to be sited in the Visual Studio’sDesigner’scomponent tray
• Intervalproperty instead of a Changemethod
• Elapsedeventinstead of a callback delegate
• Enabledpropertytostartandstopthetimer(defaultvalue=false)
• Start&StopmethodsincaseifyougetconfusedbyEnabledproperty(abovepoint)
• AutoReset- for indicating a recurring event (defaultvalue=true)
• SynchronizingObjectproperty with Invokeand BeginInvokemethods for safely calling methods on WPF elementsandWindowsFormscontrols

Examplerepresentingalltheabovefeatures:

usingSystem;

usingSystem.Timers;//TimersnamespaceratherthanThreading

classSystemTimer

{

staticvoidMain()

{

Timertimer=newTimer();//Doesn’trequireanyargs

timer.Interval=500;

timer.Elapsed+=timer_Elapsed;//Usesaneventinsteadofadelegate

timer.Start();//Startthetimer

Console.ReadLine();timer.Stop();//S

topthetimer Console.ReadLine();

timer.Start();//Restartthetimer

Console.ReadLine();

timer.Dispose();//Permanentlystopthetimer

}

staticvoidtimer_Elapsed(objectsender,EventArgse)

{

Console.WriteLine(“Tick”);

}

}

Multithreadedtimers-usethethreadpooltoallowafewthreadstoservemanytimers.Itmeansthatcallback methodorElapsedeventmaytriggeronadifferentthreadeachtimeitiscalled.
Elapsed-thiseventalwaysfiresontime—regardlessofwhetherthepreviousElapsedeventfinishedexecuting. Becauseofthis,callbacksoreventhandlersmustbethread-safe.Theaccuracyofmultithreadedtimersdependson the OS, and is typically in the 10–20 ms.
interop-wheneveryouneedgreateraccuracyusethisandcalltheWindowsmultimediatimer.Thishasaccuracy down to 1 ms and it is defined in winmm.dll.

timeBeginPeriod-CallthisfirsttoinformOSthatyouneedhightimingaccuracy timeSetEvent- call this after timeBeginPeriodto start a multimedia timer. timeKillEvent- call this when you are done, this stops the timer
timeEndPeriod-CallthistoinformtheOSthatyounolongerneedhightimingaccuracy.

YoucanfindcompleteexamplesontheInternetthatusethemultimediatimerbysearchingforthekeywords
dllimportwinmm.dlltimesetevent.

Section110.2:CreatinganInstanceofaTimer
Timersareusedtoperformtasksatspecificintervalsoftime(DoXeveryYseconds)Belowisanexampleof creating a new instance of a Timer.
NOTE:ThisappliestoTimersusingWinForms.IfusingWPF,youmaywanttolookintoDispatcherTimer

usingSystem.Windows.Forms;//TimersusetheWindows.Formsnamespace

publicpartialclassForm1:Form

{

TimermyTimer=newTimer();//createaninstanceofTimernamedmyTimer

publicForm1()

{

InitializeComponent();

}

}

Section110.3:Assigningthe”Tick”eventhandlertoaTimer
Allactionsperformedinatimerarehandledinthe”Tick”event.

publicpartialclassForm1:Form

{

TimermyTimer=newTimer();

publicForm1()

{

InitializeComponent();

myTimer.Tick+=myTimer_Tick;//assigntheeventhandlernamed”myTimer_Tick”

}

privatevoidmyTimer_Tick(objectsender,EventArgse)

{

//Performyouractionshere.

}

}

Section110.4:Example:UsingaTimertoperformasimple countdown

publicpartialclassForm1:Form

{

TimermyTimer=newTimer();

inttimeLeft=10;

publicForm1()

{

InitializeComponent();

//setpropertiesfortheTimer

myTimer.Interval=1000;

myTimer.Enabled=true;

//Settheeventhandlerforthetimer,named”myTimer_Tick”

myTimer.Tick+=myTimer_Tick;

//Startthetimerassoonastheformisloaded

myTimer.Start();

//Showthetimesetinthe”timeLeft”variable

lblCountDown.Text=timeLeft.ToString();

}

privatevoidmyTimer_Tick(objectsender,EventArgse)

{

//performtheseactionsattheintervalsetintheproperties.

lblCountDown.Text=timeLeft.ToString();

timeLeft-=1;

if(timeLeft<0)

{

myTimer.Stop();

}

}

}

Resultsin…

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