I have window with button which triggers lengthy processing. I put processing in a separate thread, but -- to my surprise -- it makes GUI frozen anyway. No control is refreshed, I cannot even move the window.
So the question is how to start the thread, so it won't interfere with GUI, i.e. so the GUI would always be up to date (while processing I change the data, and GUI displays some pieces of it)?
That is how I start thread currectly:
var thread = new Thread(doLearn);
thread.IsBackground = true;
thread.Start();
Edit 1
Jon:
I don't use any locks at all
No Join calling
The UI thread is left alone -- it simply sits there
The processing is a big loop with math operations, not even allocating memory, on UI side I have controls with binding (WPF) to data, like the number of current iteration of the main loop. It should be refreshed each time the main loop "ticks". The counter of the loop is a property which triggers OnPropertyChanged with each change (classic WPF binding).
Edit 2 -- Almost there!
Ok, so Jon hit the nail at the head (who is surprises? ;-D) -- thank you! The problem comes from changing the Counter. When I used instead the Counter, local counter the GUI was refreshed -- I mean I could move windows, but... I couldn't see display of the Counter.
What I have here -- a WPF GUI, with such data-binding
<TextBlock Text="{Binding Path=Counter"/>
and I have Counter property of course which on each change sends event PropertyChanged. One of the listeners is for sure GUI.
So, Jon answer is valid "the answer", but from good design POV not exactly, because if GUI part has to pull up the info about Counter and update the display every (let's say) 3 seconds, why would anyone use data binding? For me such approach invalidates data binding idea.
I could, theoretically, pass to the processing thread the GUI dispatcher, and do all the sending in GUI thread, and it could work (I didn't try it) but it would mean tight coupling of non-GUI part and GUI part.
So far, I have no idea how to do it "right" way. The best guess so far is to create TimerDispatcher but not at GUI side but inside the processing library, and update Counter value immediately but do all the sending from time to time (I didn't try it yet though).
Small remark: I have more properties binded actually, like IsRunning, which is changed at the beginning and at the end of processing. And those changes DO affect the display correctly -- but the Counter change triggers around 3000 notifications in 3-4 seconds. So it looks like jamming problem. I did another test -- I killed the data binding partially, so notifications were sent, but GUI was not "receiving" them -- but was listening to them. In such case the GUI was also frozen.
So, I am still listening to all advices -- thank you advance for sharing.
Edit 3
The saga continues here:
How to do the processing and keep GUI refreshed using databinding?
It should be fine as it is. Things which may be freezing your UI:
Are you locking within the UI thread, and locking on the same lock in your other thread?
Are you calling Join on the thread from your UI thread?
Are you doing some other heavy work in the UI thread?
If you could come up with a short but complete program which shows the problem, I'm sure we could help to fix it... but it certainly should be okay.
EDIT: Okay, now you've added this:
The counter of the loop is a property which triggers OnPropertyChanged with each change (classic WPF binding).
So you're updating the property from the non-UI thread? I would expect that to cause problems, because it will trigger UI changes from the wrong thread.
I suggest you take an approach such as:
Periodically update the counter via Dispatcher.BeginInvoke
Have the "UI counter" and the "worker counter" - and copy the value from the "worker counter" to the "UI counter" in the UI thread via a DispatcherTimer, essentially polling it.
There are numerous methods to run functions off the UI thread, but the easiest and generally most suitable is to look at the BackgroundWorker component. Many decent tutorials can be found. For example, here.
I put processing in a separate
thread, but -- to my surprise -- it
makes GUI frozen anyway.
I really hate to tell you, but then you did NOT put it into a separate thread. That simlpe.
There was a poster here that had a similar issue some time ago and through a mistake in his invoking code he basically had all processing before the thread started, with the thread jsut returning the result.
I faced the same situation, and solved it by two ways...
Use the thread in other class and invoke it in ur main application by creating Thread, either in its constructor OR in any method.
if u want do the it in same class, then create a Thread that call your function, and that function should invoke the Delegate.
See the examples:
public partial class Form1 : Form
{
private delegate void TickerDelegate();
TickerDelegate tickerDelegate1;
public Form1()
{
InitializeComponent();
}
//first solution
// This button event call other class having Thread
private void button1_Click(object sender, EventArgs e)
{
f = new FormFileUpdate("Auto File Updater", this);
f.Visible = true;
this.Visible = false;
}
// Second Solution
private void BtnWatch_Click(object sender, EventArgs e)
{
tickerDelegate1 = new TickerDelegate(SetLeftTicker);
Thread th = new Thread(new ThreadStart(DigitalTimer));
th.IsBackground = true;
th.Start();
}
private void SetLeftTicker()
{
label2.Text=DateTime.Now.ToLongTimeString();
}
public void DigitalTimer()
{
while (true)
{
label2.BeginInvoke(tickerDelegate1, new object[] {});
Thread.Sleep(1000);
}
}
}
Related
I have a simple app that read a database and then aftersome manipulation write the results on another one.
The first lines of code update the ui with a message for the user and an onscreen log, then is all wrapped inside a try/catch construct with usings and other try/catch annidated.
message.AppendText("** Message for the user that appear only after the try block's execution **\n");
message.ScrollToEnd();
try
{
using(SqlConnection...)
{
business code
}
}
catch
{
bbbb...
}
In the end it works, but the ui is only updated when it finishes all.
I can understand why what's inside the try must wait the end, but why the first lines don't affect the ui till the end of the successive block?
And how can I create more responsive ui?
I first tried creating a thread for any connection (one has a timout of 5 seconds), and one for the businness code.
Ok, it was overkill, but was experimenting.
I had so much problems sharing the connections between threads and interacting with the main window's ui that abandoned the idea and rewrited all as described above.
People here have suggested creating a responsive UI. This is one way to do that. At the top of your code file, add:
using System.Threading;
Move all the stuff that takes a long time to a new method:
public void LoadStuff()
{
// Do some stuff that takes a while here
}
Replace the original stuff with this code:
Thread callThread = new Thread(new ThreadStart(LoadStuff));
callThread.Start();
Now, anytime you need to update your UI from LoadStuff you have to encapsulate it (surround it) with this code. The reason for this is only the thread that creates the UI can modify it. So, we have to tell our new thread to refer back to the old thread to execute the code. Therefore, inside LoadStuff, after you compute a bunch of data, to update your UI use this:
this.Dispatcher.Invoke(new Action(() =>
{
// Code to update UI here
}));
Like others have suggested, there are others ways to increase UI speed, and I was not the first to suggest using a different thread to compute. But I just wanted to show you a way to do it.
In addition to moving long-running processes off of the UI thread, there are some UI tricks that you can do to help make user interaction feel a little better. For example, if an action takes more than about 0.1 seconds, try fading in a message (e.g. "Loading...") to let the user know that there is something happening. Once you get the data back, fade this message back out.
You may also want to try animating the UI update to avoid the "stuttering" sensation.
I'll be short and to the point. I basically need a way I can take a timer, check when the timer is up and execute something at the end of it, then loop it. For example (this code isn't serious, just example code) :
Timer1.start();
If (timer1.TimeRanOut) {
Timer2.start()
}
Or some other way to pause the timer without the GUI freezing up (I'll be running some things at a fast pace and freezing would get in the way). I'll be making this more complex by looping the entire process, like :
if (Checkbox1.checked == true; )
{
Timer1.start();
Next If (timer1.TimeRanOut) {
Timer2.start()
}
Next If (timer2.TimeRanOut) {
Timer3.start()
}
And so on. Any solutions?
I would suggset working with Tasks. you set up a task to do something (it can just wait for X seconds, than it is a timer) than you set continueWith to assign a new task to run when the first one is finshed.
You can read more about this here:
http://msdn.microsoft.com/en-us/library/dd537612.aspx
And by the way, you really should not run heavy calculations on the UI thread itself.
If you decide to use tasks - that would be fine. Otherwise , you need to create background thread and do the work there.
Edit:
After some clarification from the OP , I will try to explain the basics or working with UI and background threads:
When you run a winforms/WPF application, all of the user interface events are handled in a single thread - the UI thread. it goes over all of the events and processes them.
If long calculation occupy this thread, the UI will become "stuck" and o responsive. see:
UI freezes on heavy calculation
That is why, any long calculations should be done on another thread, in the background.
In the above post's answer there is an example on how to do this.
You could use the System.Threading.Timer. You would then make use of its single shot capability (see Change method). Such you may chain several timers.
The callback of this timer runs on the thread pool so your UI doesn't freeze.
I've found what looks like a very simple solution to my current situation.
My current situation is that I want to do some I/O-heavy operations on a new Thread, so that I do not bog down my GUI Thread. I have a function written, as a member of my Form, that does these I/O operations already, but running it on the GUI Thread really makes the application a pain to use. So my plan was to just run this function in a new Thread. So, I created a Thread variable, in my form, and am trying to get it to use that function as the ThreadStart parameter. It does not seem to like it, though.
I found an elegant looking solution, as a response to another thread, here.
///...blah blah updating files
string newText = "abc"; // running on worker thread
this.Invoke((MethodInvoker)delegate {
someLabel.Text = newText; // runs on UI thread
});
///...blah blah more updating files
From the looks of that response, I could run this function in a new Thread and then use an anonymous function to update my Form when the Thread has finished its calculations. I'm just not good enough to fill in the blanks from that response, though.
Everything I seem to read about Threads says that my ThreadStart function needs to be a static method in a new class. That response seems to suggest that I can do it within my Form class though, so that the this reference still references my Form instance. Otherwise, if my ThreadStart parameter were a different class, I'd have to pass in references to the Form instance, and that seems like more code, right?
Would anybody mind helping me fill in the context for that response? Thanks in advance!
There are a lot of ways you can do this. A very simple, straightforward one that's been around for a number of versions is to use the BackgroundWorker. It is designed for exactly this case. It has a DoWork method that runs in a background thread, and a Completed event that is fired after the work is done which runs in the UI thread (so you don't need to call invoke or anything to update the UI with the results). It even has support built in for reporting progress (the report progress event also runs in the UI thread) so you can easily update a progress bar or status text.
MSDN has some examples as well, and you can find lots more through some simple searches.
Another option, made available through C# 4.0, is to use Tasks. You can start a new task which will be run in a background thread, and then you can add a continuation which will be in the UI thread.
Here is a simple example:
private void button1_Click(object sender, EventArgs e)
{
Task.Factory.StartNew(() => doStuffInBackground())
.ContinueWith(task => updateUI(), TaskScheduler.FromCurrentSynchronizationContext());
}
private void updateUI()
{
throw new NotImplementedException();
}
private void doStuffInBackground()
{
throw new NotImplementedException();
}
You can of course do whatever you want in the actual lambdas that I have there, or you could even remove the lambdas and put methods in there directly as long as you ensure the signatures are correct. You could also continue chaining these continuations if you wanted, allowing you to, for example, to task 1, update a label, then do task 2, update a label, etc. The main disadvantage is that it's not good at updating a progress bar frequently inside of a loop, the way a BackgroundWorker can.
I seem to have a problem executing commands in the correct order, I have a method in my Program:
private void GenerateButton_Click(object sender, EventArgs e)
{
Statuslabel.Text = "Working...";
LongMethod();
//Call to another Method of another class which takes 15-20 seconds to execute
Statuslabel.Text = "Done";
}
the problem seems to be that instead of assigning "Working" to the status label and THEN calling the LongMethod, the Program seems to execute LongMethod() first, and then it changes Status Label's text to "Working" for a split second and then immediately changes it to "Done".
Oh, and the UI is locked up during the LongMethod() execution, because the Program is SingleThreaded.
I tried threads earlier, but for the life of me I couldn't get the syntax right, I tried:
Thread MyThread = new Thread(LongClass.LongFunction);
Thread MyThread = new Thread(new ThreadStart(LongClass.LongFunction));
Where LongClass is the class which contains LongFunction as a static method.
I will check out the background worker now.
You should execute LongMethod on another thread so that the UI thread doesn't block while it's running.
Remember, updating the UI is running code just like anything else. While your long-running method is running, that thread is not doing any of the tasks necessary to redraw the user interface. Changing a UI element does not stop everything and re-draw it because suppose you changed a thousand UI elements; you wouldn't expect a redraw after each one; you'd expect them all to happen at once, after you'd made all the changes.
Long story short, if you want to refresh the UI after the update but before the long-running code -- that is, you don't care about hanging the UI but you at least want it to update -- then insert a call that explicitly refreshes the UI.
Some have suggested "DoEvents" as a workaround. This can work, but it is super dangerous. For two reasons. First, suppose the user clicks a button twice. During the processing of the first click, you do a DoEvents, and so you then recurse and hey, now you have suspended the processing of the first button click so that you can process the second button click... and that can't be good.
Second, suppose you're processing an event, and you do a DoEvents, which causes you to start processing another event, and then while you're doing that, you do a DoEvents, and that causes you to start processing a third event... and this keeps going forever. When do you finish processing the first event? Potentially never. Remember "DoEvents" basically means "concentrate on what just happened at the expense of what you were already working on".
While I think Jason's answer to use another thread is the way to go, there is another "evil" option.
Statuslabel.Text = "Working...";
Application.DoEvents();
LongMethod();
Statuslabel.Text = "Done";
I have a WinForm drawing a chart from available data.
I programmed it so that every 1 secong the Winform.Timer.Tick event calls a function that:
will dequeue all data available
will add new points on the chart
Right now data to be plotted is really huge and it takes a lot of time to be executed so to update my form. Also Winform.Timer.Tick relies on WM_TIMER , so it executes in the same thread of the Form.
Theses 2 things are making my form very UNresponsive.
What can I do to solve this issue?
I thought the following:
moving away from usage of Winform.Timer and start using a System.Threading.Timer
use the IsInvokeRequired pattern so I will rely on the .NET ThreadPool.
Since I have lots of data, is this a good idea?
I have fear that at some point also the ThreadPool will be too long or too big.
Can you give me your suggestion about my issue?
Thank you very much!
AFG
It is a good idea to move the fetching of the data to a Thread. You can use a BackgroundWorker that gets the data in an endless loop and
use the UpdateProgress event to update the chart. This takes care of the InvokeRequired business
Use a Sleep(remainingTime) inside the loop to get a desired frequency.
It is quite unlikely you'll be ahead by using a background timer. Your chart control almost certainly requires it to be updated from the same thread is was created on. Any kind of control that has a visible appearance does. Which requires you to use Control.BeginInvoke in the Elapsed event handler so that the update code runs on the UI thread. Dequeueing data isn't likely to be expensive, you will have actually have made it slower by invoking. And still not have taken the pressure off the UI thread.
You'll also have a potentially serious throttling problem, the timer will keep on ticking and pump data, even if the UI thread can't keep up. That will eventually crash your program with OOM.
Consider instead to make the code that updates the chart smarter. A chart can only display details of the data if such details are at least a pixel wide. Realistically, it can only display 2000 pixels with useful information. That's not much, updating 2000 data points shouldn't cause any trouble.
I would go with a System.Timers.Timer over a BackgroudWorker in an endless loop.
The BackgroundWorker is executed from a ThreadPool and is not meant to run for the lifetime of your application.
Motivation for System.Timers.Timer:
Each elapsed event is executed from a ThreadPool, won't hang your UI thread.
Using a combination of locks and enabling/disabling the timer we can get the same frequency as if we did a Thread.Sleep(xxx) in an endless loop.
Cleaner and more obvious as to what you are trying to achieve
Here's my suggestion:
Disabling the timer at the beginning of the method, then re-enabling it again at the end, will cater for the case where the amount of work done in the elapsed event takes longer than the timer interval. This also ensures the timer between updates is consistent. I've added a lock for extra precaution.
I used an anonymous method to update the UI thread, but you can abviously do that however you want, as long as you remember to Invoke, it's also a good idea to check the InvokeRequired property
private readonly object chartUpdatingLock = new object();
private void UpdateChartTimerElapsed(object sender, ElapsedEventArgs e)
{
// Try and get a lock, this will cater for the case where two or more events fire
// in quick succession.
if (Monitor.TryEnter(chartUpdatingLock)
{
this.updateChartTimer.Enabled = false;
try
{
// Dequeuing and whatever other work here..
// Invoke the UI thread to update the control
this.myChartControl.Invoke(new MethodInvoker(delegate
{
// Do you UI work here
}));
}
finally
{
this.updateChartTimer.Enabled = true;
Monitor.Exit(chartUpdatingLock);
}
}
}