I understand that a Thread will terminate when all of the code it has been assigned is done, but how can I make it so that it stays around waiting for an event? Here is a simple look at my code so you can understand better what my problem is:
public static class TimeUpdater
{
static TimeUpdater()
{
//Initialize the Timer object
timer = new Timer();
timer.Interval = 1000;
timer.Tick += timer_Tick;
}
public static void StartTimer()
{
timer.Start();
}
private static void timer_Tick(object sender, EventArgs e)
{
//Do something
}
}
From the main Thread, here is how I am calling these methods:
Thread timeThread = new Thread(TimeUpdater.StartTimer);
timeThread.Name = "Time Updater";
timeThread.Start();
What this does is it goes inside the StartTimer() method, runs it, and then the thread terminates without ever entering the timer_Tick event handler. If I call StartTimer() from the main thread it works fine.
Anyone can spot the problem? Cheers.
You are starting the timer on a separate thread. Starting a timer is a very fast operation. That's why your thread completes immediately. Tick events are started on the thread-pool asynchronously when the time is due.
If you want a thread wait for something then you should insert code into the thread procedure to wait on something. At the moment you do not wait for anything.
If you want to run the timer procedure, just call it.
Apparently I didn't need to use a Timer object. Here is how I made it work:
public static void StartTimer()
{
while (true)
{
UpdateTime();
Thread.Sleep(1000);
}
}
Thanks for the help guys!
In your StartTimer method you can spin around an infinite loop and call Thread.Sleep to delay execution when needed. I see you have already figured that out though. An alternate idea is to use a timer, but instead of starting it from a worker thread start it from the main thread. You really do not need to be manually creating threads at all here.
Related
I have a problem with the Timer in a Windows Forms app. The archiver that needs the Timer to note the time of archiving. However something is interrupting the timer?
I suspect it is the streams. Any advice on what could cause the timer to be interrupted?
public partial class Form1 : Form
{
int timerCounter = 0;
System.Windows.Forms.Timer timer = new System.Windows.Forms.Timer();
public Form1()
{
InitializeComponent();
timer.Interval = 1000;
timer.Enabled = true;
}
public void button2_Click(object sender, EventArgs e)
{
timer.Start();
timer.Tick += new EventHandler(timer1_Tick);
// code for archiving, streams
timer.Stop();
MessageBox.Show("Archive was created! :)");
}
public void timer1_Tick(object sender, EventArgs e)
{
this.label7.Text = (++timerCounter).ToString();
}
}
The Windows Forms timer is not multi-threaded. That means, the tick event only fires when the program is idle (receives messages through its message queue). In your program this doesn't seem to be the case. You can easily check this: If your UI is responsive during the archiving process, then the Forms.Timer runs also and the problem is somewhere else. If it is not responsive, then the form (and the timer as a consequence) is blocked (no messages in the application's message queue are processed).
There are two ways out of this:
To do what you want to achieve, you can use System.Timers.Timer or System.Threading.Timer, as they run asynchronously in the background. The UI still won't update (the timer method would stop), however, as the UI is still blocked (see above).
The other way is to use a background worker for the archiving process (this then runs in another thread). The UI and the timer keep responsive.
First of all you should to know that long running operation should be performent in another than UI thread. So, you create a proccessing thread which do archiving itself and also it notifies UI by using Control.Invoke method. msdn description of Control.Invoke
Initially i thought that you are performing your archiving in the background thread. If it is not so - you should consider using BackgroundWorker for executing the operation in the background (here's some examples).
Here is the simpler solution, though:
Try to add Application.DoEvents() in your button2_Click handler (I guess you are waiting for 'streams' to finish the archiving). For timer to fire and for label7 to redraw its new text value the redraw event should be processed.
The use of timer here is unnecessary why don t you just use TimeSpan
public void button2_Click(object sender, EventArgs e)
{
DateTime startTime = DateTime.Now;
// code for archiving, streams
TimeSpan diff = DateTime.Now - startTime;
MessageBox.Show("Archive was created! in " + diff.TotalSeconds + " seconds.");
}
I am using System.Timers in my program.
As we know each interval new thread is created to handle the OnTimedEvent.
I am looking for way to force the system to wait creating a new thread if the previous thread is still running.
My OnTimedEvent execute some method and I would like to wait until the method is finished
Any idea how to do that?
You are mistaken in the sense that no new thread will be created when the Elapsed event is fired. The event will be raised on the the .NET threadpool, so an arbitrary thread will process it.
One way to do what you want is to Stop the timer at the start of your event handler and to Start it again once it is finished. Like this:
var timer = new System.Timers.Timer(1000);
timer.Elapsed += HandleTimerElapsed;
timer.Start();
...
private void HandleTimerElapsed(object s, ElapsedEventArgs e)
{
var t = (System.Timers.Timer)s;
t.Stop();
try {
... do some processing
}
finally { // make sure to enable timer again
t.Start();
}
}
The other option is to set the AutoReset property of the timer to false. This way the timer will only be raised once. Then you can call Start when you want it to start again. So the above code would change to include a timer.AutoReset = false; at the beginning and then you don't need to call Stop inside the handler. This is a bit safer as the above method probably has a race condition in the sense that if the system is under load your handler might not be guaranteed to execute before the timer elapses again.
I have an issue with the System.Timers.Timer object. I use the timer object to perform a task at regular intervals. In the timer constructor I call the method doing the work ( DoTimeCheck() ), to ensure that the task is run once at startup also. The work (at regular intervals) is done in a BackgroundWorker.
I call the timer with this:
UpdaterTimer ut = UpdaterTimer.UpdaterTimerInstance;
My problem is that I need to delay the first run of the task with 3 minutes(the one that runs at application startup). Subsequent runs (Elapsed event) should run without delay. I thought of doing this by calling
System.Threading.Thread.Sleep(TimeToDelayFirstRunInMiliseconds);
but this fails, because it also hangs the UI of the app (main thread) making it unusable. How can I delay the first run of DoTimeCheck() without hanging the UI?
The code of the timer is below. If the issue is not presented in a clear manner please let me know and I will edit. Thank you in advance.
public sealed class UpdaterTimer : Timer
{
private static readonly UpdaterTimer _timer = new UpdaterTimer();
public static UpdaterTimer UpdaterTimerInstance
{
get { return _timer; }
}
static UpdaterTimer()
{
_timer.AutoReset = true;
_timer.Interval = Utils.TimeBetweenChecksInMiliseconds;
_timer.Elapsed += new ElapsedEventHandler(_timer_Elapsed);
_timer.Start();
DoTimeCheck();
}
static void _timer_Elapsed(object sender, ElapsedEventArgs e)
{
DoTimeCheck();
}
private static void DoTimeCheck()
{
//... work here
}
}
One way of doing this would be to give the Timer Interval an initial value (e.g. 3 minutes). Then, in your Elapsed event handler, you could change the interval to your regular value which will be used from then on.
_timer.Interval = Utils.InitialCheckInterval;
static void _timer_Elapsed(object sender, ElapsedEventArgs e)
{
if (_timer.Interval == Utils.InitialCheckInterval)
{
_timer.Interval = Utils.RegularCheckInterval;
}
DoTimeCheck();
}
It appears (although you've not shown that code) that you're calling Sleep(TimeToDelayFirstRunInMiliseconds); on the main/GUI thread, so that's what's causing your UI thread to hang. Instead, you should set your timer to be delayed by 3 minutes on the first run, then once it runs you change the timer again to run at the frequency you desire for all the subsequent runs.
Your UI resides on the same thread, so when you put the thread to sleep, it will cause your UI to hang as well. You need to run the timer on a different thread.
You're already using timers fine it seems. Just use another one to do a three minute delay before you start up your other timer.
timer = new Timer();
timer.AutoReset = false;
timer.Interval = 3*60*1000;
timer.Elapsed += startOtherTimerMethod;
timer.Start();
Edit: I should note that this is much the same as Peter Kelly's answer except that his solution is more elegant since it uses just one timer, no extra methods and takes advantage of the fact that the timer is changeable between runs. If you liked this answer, you'll love his. ;-)
Your UI needs a seperate thread, currently you are also sleeping the UI. Check this post.
You should not use thread.sleep in this situation you should use the winforms control
BackgroundWorker which never locks the main UI. You can write your logic there.
example here:
http://www.knowdotnet.com/articles/backgroundworker.html
Use a System.Threading.Timer - the constructor takes a parameter for the delay of the first run and an interval for the subsequent runs.
What I want to do is to use the System.Threading.Timer to execute a method with a interval.
My example code looks like this atm.
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
System.Threading.Timer t1 = new System.Threading.Timer(WriteSomething, null, TimeSpan.FromSeconds(0), TimeSpan.FromSeconds(10));
}
private void button1_Click(object sender, EventArgs e)
{
textBox1.Clear();
}
public void WriteSomething(object o)
{
textBox1.Text = "Test";
}
}
}
Isn't this suppost to execute the WriteSomething method every 10'th second. What rly happens is that the WriteSomething is executed when I run my application and after 10 seconds the application closes. Think I have missunderstood how this works, can anyone tell me how to do this with the System.Threading.Timer.
thanks in advance, code examples are very welcome
The more likely scenario is that it crashes after 10 seconds. You cannot touch any controls in the callback, it runs on the wrong thread. You'd have to use Control.BeginInvoke(). Which makes it utterly pointless to use a System.Threading.Timer instead of a System.Windows.Forms.Timer.
Be practical. Make it 100 milliseconds so you don't grow a beard waiting for the crash. And don't use an asynchronous timer to update the UI, it is useless.
FYI, there is nothing about System.Windows.Forms timer that doesn't allow you to create in code (it's not just a "drag-and-drop" timer). Code:
Constructor code:
System.Windows.Forms.Timer timer = new System.Windows.Forms.Timer();
timer.Tick += OnTimerTick;
timer.Interval = 10000;
timer.Start();
Event Handler:
private void OnTimerTick(object sender, EventArgs e)
{
// Modify GUI here.
}
Just to reiterate what Hans said, in a WinForms application all GUI elements are not inherently thread-safe. Almost all methods / properties on Control classes can only be called on the thread the GUI was created on. The System.Threading.Timer invokes its callback on a thread pool thread, not the the thread you created the timer on (see reference below from MSDN). As Hans said, you probably want a System.Windows.Forms.Timer instead, that will invoke your callback on the correct thread.
You can always verify whether you can call methods on a Control (assuring you're on the correct thread) by using the code:
System.Diagnostics.Debug.Assert(!InvokeRequired);
inside your event handler. If the assert trips, you're on a thread that cannot modify this Control.
Quote from MSDN help on System.Threading.Timer on the callback method you passed in the constructor:
The method does not execute on the
thread that created the timer; it
executes on a ThreadPool thread
supplied by the system.
Common error: need to keep timer variable as class member as garbage collector may kill it.
So I have a program that has a list of timers. Each of the timers has a tick event and lets just say for example, i have 10 timers started (all are in the List).
What is the best way to sit forever (or until i tell it to stop)? Should I just have a while loop?
foreach(Timer t in _timers)
{
t.Start();
}
while(true)
{
Application.DoEvents();
System.Threading.Thread.Sleep(5000);
}
I have a feeling that this isn't the best way...
-- Update
Here's my entire program:
public static void Main()
{
// set some properties and set up the timers
foreach(Timer t in _timers)
{
t.Start();
}
while(true)
{
Application.DoEvents();
System.Threading.Thread.Sleep(5000);
}
}
Thats it. There is no UI, there's nothing else. If I don't have the while loop, then the program just finishes.
Use an EventWaitHandle or array of EventWaitHandles to block thread execution by using the WaitOne() or WaitAll() methods.
http://msdn.microsoft.com/en-us/library/kad9xah9.aspx
So for example
ManualResetEvent mre = new ManualResetEvent(false);
mre.WaitOne();
will wait for eternity.
edit
Since you're making a service, you might want to read this article.
By the Application.DoEvents, I assume you are on a UI thread here. It is never a good idea to keep the UI thread active (even with DoEvents). Why not just start the timers and release control back to the message pump. When the events tick it'll pick up the events.
Why do you want to loop?
Re the update; which Timer are you using? If you use System.Timers.Timer (with the Elapsed event) then it isn't bound to the message-loop (it fires on a separate thread): you can just hang the main thread, perhaps waiting on some exit condition:
using System;
using System.Timers;
static class Program {
static void Main() {
using (Timer timer = new Timer()) {
timer.Interval = 2000;
timer.Elapsed += delegate {
Console.Error.WriteLine("tick");
};
timer.Start();
Console.WriteLine("Press [ret] to exit");
Console.ReadLine();
timer.Stop();
}
}
}
You could wait on a condition variable, or select() on a socket.
Depending on how you're exiting the program, you might consider using only nine timers and have the tenth activity part of the main thread of your code.
Each of those timers is a separate thread and should be handled carefully.
DoEvents is considered 'evil' and should be avoided. http://msdn.microsoft.com/en-us/library/system.windows.forms.application.doevents.aspx