Develop Reference

Find out which winforms controls are accessed from a background thread

We have built a huge winforms project, already in progress for multiple years.
Sometimes, our users get an exception which looks like this one.
The resolution of this problem seems to be:
don't acces UI components from a background thread
.
But since our project is a very big project with a lot of different threads, we don't succeed in finding all these.
Is there a way to check (with some tool or debugging option) which components are called from a background thread?
To clarify:
I created a sample winforms project with a single Form, containing two Button
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
button1.Text = "Clicked!";
}
private void button2_Click(object sender, EventArgs e)
{
Task.Run(() =>
{
button2.BackColor = Color.Red; //this does not throw an exception
//button2.Text = "Clicked"; //this throws an exception when uncommented
});
}
}
The background color of button2 is set to red when the button is clicked. This happens in a background thread (which is considered bad behavior). However, it doesn't (immediately) throw an exception. I would like a way to detect this as 'bad behavior'. Preferably by scanning my code, but if it's only possible by debugging, (so pausing as soon as a UI component is accessed from a background thread) it's also fine.

I've got 2 recommendations to use together, the first is a Visual Studio Plugin called DebugSingleThread.
You can freeze all the threads and work on one at a time (obviously the non-main-UI threads) and see each threads access to controls. Tedious I know but not so bad with the second method.
The second method is to get the steps in order to reproduce the problem. If you know the steps to reproduce it, it will be easier to see whats causing it. To do this I made this User Action Log project on Github.
It will record every action a user makes, you can read about it here on SO: User Activity Logging, Telemetry (and Variables in Global Exception Handlers).
I'd recommend you also log the Thread ID, then when you have been able to reproduce the problem, go to the end of the log and work out the exact steps. Its not as painful as it seems and its great for getting application telemetry.
You might be able to customise this project, eg trap a DataSource_Completed event or add a dummy DataSource property that sets the real Grids DataSource property and raises an INotifyPropertyChanged event - and if its a non-main thread ID then Debugger.Break();.
My gut feeling is you're changing a control's (eg a grid) data source in a background thread (for that non-freeze feel) and thats causing a problem with synchronisation. This is what happened to the other DevExpress customer who experienced this. Its discussed here in a different thread to the one you referenced.

Is your app set to ignore cross threading intentionally?
Cross-thread operations should be blowing up all the time in winforms. It checks for them like crazy in just about every method. for a starting point check out https://referencesource.microsoft.com/#System.Windows.Forms/winforms/Managed/System/WinForms/Control.cs.
Somewhere in your app, somebody might have put this line of code:
Control.CheckForIllegalCrossThreadCalls = False;
Comment that out and run the app, then follow the exceptions.
(Usually you can fix the problem by wrapping the update in an invoke, e.g., in a worker thread if you see textbox1.text=SomeString; change it to `textbox.invoke(()=>{textbox1.text=SomeString;});.
You may also have to add checking for InvokeRequired, use BeginInvoke to avoid deadlocks, and return values from invoke, those are all separate topics.
this is assuming even a moderate refactor is out of the question which for even a medium sized enterprise app is almost always the case.
Note: it's not possible to guarantee successful discovery of this case thru static analysis (that is, without running the app). unless you can solve the halting problem ... https://cs.stackexchange.com/questions/63403/is-the-halting-problem-decidable-for-pure-programs-on-an-ideal-computer etc...

I did this to search for that specific situation but of course, need to adjust it to your needs, but the purpose of this is to give you at least a possibility.
I called this method SearchForThreads but since it's just an example, you can call it whatever you want.
The main idea here is perhaps adding this Method call to a base class and call it on the constructor, makes it somewhat more flexible.
Then use reflection to invoke this method on all classes deriving from this base, and throw an exception or something if it finds this situation in any class.
There's one pre req, that is the usage of Framework 4.5.
This version of the framework added the CompilerServices attribute that gives us details about the Method's caller.
The documentation for this is here
With it we can open up the source file and dig into it.
What i did was just search for the situation you specified in your question, using rudimentary text search.
But it can give you an insight about how to do this on your solution, since i know very little about your solution, i can only work with the code you put on your post.
public static void SearchForThreads(
[System.Runtime.CompilerServices.CallerMemberName] string memberName = "",
[System.Runtime.CompilerServices.CallerFilePath] string sourceFilePath = "",
[System.Runtime.CompilerServices.CallerLineNumber] int sourceLineNumber = 0)
{
var startKey = "this.Controls.Add(";
var endKey = ")";
List<string> components = new List<string>();
var designerPath = sourceFilePath.Replace(".cs", ".Designer.cs");
if (File.Exists(designerPath))
{
var designerText = File.ReadAllText(designerPath);
var initSearchPos = designerText.IndexOf(startKey) + startKey.Length;
do
{
var endSearchPos = designerText.IndexOf(endKey, initSearchPos);
var componentName = designerText.Substring(initSearchPos, (endSearchPos - initSearchPos));
componentName = componentName.Replace("this.", "");
if (!components.Contains(componentName))
components.Add(componentName);
} while ((initSearchPos = designerText.IndexOf(startKey, initSearchPos) + startKey.Length) > startKey.Length);
}
if (components.Any())
{
var classText = File.ReadAllText(sourceFilePath);
var ThreadPos = classText.IndexOf("Task.Run");
if (ThreadPos > -1)
{
do
{
var endThreadPos = classText.IndexOf("}", ThreadPos);
if (endThreadPos > -1)
{
foreach (var component in components)
{
var search = classText.IndexOf(component, ThreadPos);
if (search > -1 && search < endThreadPos)
{
Console.WriteLine($"Found a call to UI thread component at pos: {search}");
}
}
}
}
while ((ThreadPos = classText.IndexOf("Task.Run", ++ThreadPos)) < classText.Length && ThreadPos > 0);
}
}
}
I hope it helps you out.
You can get the Line number if you split the text so you can output it, but i didn't want to go through the trouble, since i don't know what would work for you.
string[] lines = classText.Replace("\r","").Split('\n');

Try that:
public static void Main(string[] args)
{
// Add the event handler for handling UI thread exceptions to the event.
Application.ThreadException += new ThreadExceptionEventHandler(exception handler);
// Set the unhandled exception mode to force all Windows Forms errors to go through the handler.
Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException);
// Add the event handler for handling non-UI thread exceptions to the event.
AppDomain.CurrentDomain.UnhandledException += // add the handler here
// Runs the application.
Application.Run(new ......);
}
Then you can log the message and the call stack and that should give you enough information to fix the issue.

I recommend you update your GUI to handle this situation automatically for your convenience. You instead use a set of inherited controls.
The general principle here is to override the property Set methods in a way to make them Thread Safe. So, in each overridden property, instead of a straight update of the base control, there's a check to see if an invoke is required (meaning we're on a separate thread the the GUI). Then, the Invoke call updates the property on the GUI thread, instead of the secondary thread.
So, if the inherited controls are used, the form code that is trying to update GUI elements from a secondary thread can be left as is.
Here is the textbox and button ones. You would add more of them as needed and add other properties as needed. Rather than putting code on individual forms.
You don't need to go into the designer, you can instead do a find/replace on the designer files only. For example, in ALL designer.cs files, you would replace System.Windows.Forms.TextBox with ThreadSafeControls.TextBoxBackgroundThread and System.Windows.Forms.Button with ThreadSafeControls.ButtonBackgroundThread.
Other controls can be created with the same principle, based on which control types & properties are being updated from the background thread.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace ThreadSafeControls
{
class TextBoxBackgroundThread : System.Windows.Forms.TextBox
{
public override string Text
{
get
{
return base.Text;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.Text = value; });
else
base.Text = value;
}
}
public override System.Drawing.Color ForeColor
{
get
{
return base.ForeColor;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.ForeColor = value; });
else
base.ForeColor = value;
}
}
public override System.Drawing.Color BackColor
{
get
{
return base.BackColor;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.BackColor = value; });
else
base.BackColor = value;
}
}
}
class ButtonBackgroundThread : System.Windows.Forms.Button
{
public override string Text
{
get
{
return base.Text;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.Text = value; });
else
base.Text = value;
}
}
public override System.Drawing.Color ForeColor
{
get
{
return base.ForeColor;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.ForeColor = value; });
else
base.ForeColor = value;
}
}
public override System.Drawing.Color BackColor
{
get
{
return base.BackColor;
}
set
{
if (this.InvokeRequired)
this.Invoke((MethodInvoker)delegate { base.BackColor = value; });
else
base.BackColor = value;
}
}
}
}

Visual Studio during Debugging: The function evaluation requires all threads to run

I'm suddenly getting a strange error while debugging. Up to now the variable in the watch windows has been showing correctly. Now I am always getting this error message in the watch windows:
The function evaluation requires all threads to run
I am not able to check any variable anymore. I am not explicitly working with threads. What can I do to get it working again?
I already disabled, as mentioned in some forums, the function: "Enable property Evaluation and other implicit function Calls" in the option window of the debugger. But without success, and it gives me this error:
Error Implicit Function evaluation disabled by the user

From the msdn forum:
This isn't an error in and of itself, but more of a feature of your debugger.
Some properties require code to be executed in order for the property to be read, but if this requires cross-thread interaction, then other threads may have to run as well. The debugger doesn't do this automatically, but certainly can, with your permission.
Just click the little evaluate icon and it will run your code and evaluate the property.
For further details on this behaviour check this excelent article

I ran into this issue when just trying to get items from a table called "AGENCY" using Entity Framework:
var agencies = db.AGENCY.OrderBy(e => e.FULLNAME);
Hovering over agencies in debug mode, clicking to expand the options, and clicking Results would give the dreaded "The function evaluation requires all threads to run" with a "Do Not Enter" icon at the end that, on which, clicking did nothing.
2 possible solutions:
Add .ToList() at the end:
var agencies = db.AGENCY_TABLE.OrderBy(e => e.FULLNAME).ToList();
List<AGENCY_TABLE> agencies = db.AGENCY_TABLE.OrderBy(e => e.FULLNAME).ToList();
Credit goes to Hp93 for helping me come to this solution. In the comments on MUG4N's answer where I found this solution, it also mentions trying .Any() instead of .ToList(), but this gives a Boolean instead of a <T>, like <AGENCY> is, so it probably wouldn't help.
Workaround - try a different path in the debug options. I found that I could click on the "Non-Public Members" > "_internalQuery" > ObjectQuery > Results View and get my values that way.

MUG4N has indeed provided a correct answer however if you hover over the line of code in debug, you may be looking at something like the below. If so, click the little re-evaluate icon highlighted in the image below...
NB: I obtained this image by pinning, normally the re-evaluate icone are in the middle of the window and not down the left hand column.

You should make thread safe call because accessing Windows form controls are not Thread safe in multithreading.
This is my simple code which makes Thread safe call and sets Progress bar.
public partial class Form1 : Form
{// This delegate enables asynchronous calls for setting
// the text property on a TextBox control.
delegate void StringArgReturningVoidDelegate(string text);
private Thread demoThread = null;
public int Progresscount = 0;
static EventWaitHandle waithandler = new AutoResetEvent(false);
public Form1()
{
InitializeComponent();
}
public static bool CheckForInternetConnection()
{
try
{
using (var client = new WebClient())
{
using (var stream = client.OpenRead("http://www.google.com"))
{
return true;
}
}
}
catch
{
return false;
}
}
public void Progressincrement()
{
waithandler.WaitOne();
while (CheckForInternetConnection()==true)
{
if (Progresscount==100)
{
break;
}
SetLabel("Connected");
Progresscount += 1;
SetProgress(Progresscount.ToString());
Thread.Sleep(TimeSpan.FromSeconds(1));
}
if (Progresscount <100)
{
Startthread();
}
SetLabel("Completed");
}
public void Startthread ()
{
this.demoThread= new Thread(new ThreadStart(Progressincrement));
this.demoThread.Start();
SetLabel("Waiting for connection");
while (CheckForInternetConnection() == false) ;
waithandler.Set();
}
private void SetLabel(string text)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (this.label1.InvokeRequired)
{
StringArgReturningVoidDelegate d = new StringArgReturningVoidDelegate(SetLabel);
this.Invoke(d, new object[] { text });
}
else
{
this.label1.Text = text;
}
}
private void SetProgress(string Value)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (this.progressBar1.InvokeRequired)
{
StringArgReturningVoidDelegate d = new StringArgReturningVoidDelegate(SetProgress);
this.Invoke(d, new object[] {Value});
}
else
{
this.progressBar1.Value = Convert.ToInt32(Value);
}
}
private void Form1_Load(object sender, EventArgs e)
{
Startthread();
}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show("Responsive");
}
}
For more information MSDN

This isn't an error, but more of a feature of your debugger.
The debugger doesn't do this automatically, but certainly can, with users permission. Just click the little space icon and it will run the code and evaluate the property.

I use the next workaround to pass:
var OtherThreadField = "";
Invoke(new MethodInvoker(delegate
{
OtherThreadField = ExecuteNeededMEthod();
}));
Now i have a value for OtherThreadField.

I faced the same issue and solved .The Issue arise due to username and password ,in SQL connection there is user and password but in code there no user and password. so I enable the user and the password and the issue solved

For me, this happened when trying to break on a line that accesses a complex object instance contained by a Settings Class.
A breakpoint on the following if results in Settings.Default.FindSettings with the value being "The function evaluation requires all threads to run." If I press the force eval button, it is null. Stepping with the force eval button click or not enters the if block and initializes the object. If I remove the breakpoint and add a new breakpoint following the if block, the Settings.Default.FindSettings deserializes properly with the expected values.
if (Settings.Default.FindSettings == null)
{
Settings.Default.FindSettings = new FindSettings();
}
After trial and error, I added the following code before the above if block to access the settings prior to breaking. This seems to reliably fix the problem. I do not need it in production so I wrap in conditional compiler directive. I have a comment in the code instead of a non-descript discard:
#if DEBUG
var _ = Settings.Default.FindSettings;
#endif
I am not sure if the above line would be optimized out in production since it has side effects. As I only need it while debugging, I have not checked.

The Code Works Fine When Debugging, But it Doesn't work when it runs without Debugging

string entry = Titleentry.Text;
webBrowser1.Navigate("http://www.bookdepository.com/search/advanced");
//HtmlElementCollection bookCollection;
while (webBrowser1.ReadyState != WebBrowserReadyState.Complete)
{
Application.DoEvents();
}
HtmlElementCollection bookCollection = webBrowser1.Document.GetElementsByTagName("input");
foreach (HtmlElement curElement in bookCollection)
{
if ((curElement.GetAttribute("id").ToString() == "searchTitle"))
{
curElement.SetAttribute("value", entry);
}
}
HtmlElementCollection filterCollection = webBrowser1.Document.GetElementById("filterSortBy").GetElementsByTagName("option");
List<HtmlElement> filterList = new List<HtmlElement>();
foreach (HtmlElement filterItem in filterCollection) { filterList.Add(filterItem); }
HtmlElement filterElement =
(HtmlElement)filterList.Where(filterOption => filterOption.GetAttribute("value").Equals("price_low_high", StringComparison.InvariantCultureIgnoreCase)).SingleOrDefault();
if (filterElement.GetAttribute("value").Equals("price_low_high"))
{
filterElement.SetAttribute("Selected", "price_low_high");
filterElement.InvokeMember("click");
}
bookCollection = webBrowser1.Document.GetElementsByTagName("button");
foreach (HtmlElement curElement in bookCollection)
{
if (curElement.GetAttribute("id").Equals("searchSubmit"))
{
curElement.InvokeMember("click");
}
}
while (webBrowser1.ReadyState != WebBrowserReadyState.Complete)
{
Application.DoEvents();
}
MessageBox.Show("Loaded");
System.Timers.Timer myTimer = new System.Timers.Timer(5000);
myTimer.Enabled = true;
myTimer.Start();
myTimer.Stop();
if (webBrowser1.ReadyState == WebBrowserReadyState.Complete) //from here on the code doesnt work.
{
HtmlElementCollection avCollection = webBrowser1.Document.GetElementById("filterAvailability").GetElementsByTagName("option");
List<HtmlElement> avList = new List<HtmlElement>();
foreach(HtmlElement avItem in avCollection)
{
avList.Add(avItem);
}
HtmlElement avElement =
(HtmlElement)avList.Where(avOption => avOption.GetAttribute("value").Equals("1")).SingleOrDefault();
if (avElement.GetAttribute("value").Equals("1"))
{
avElement.SetAttribute("Selected", "1");
avElement.InvokeMember("click");
}
bookCollection = webBrowser1.Document.GetElementsByTagName("button");
foreach (HtmlElement curElement in bookCollection)
{
if (curElement.GetAttribute("id").Equals("searchSubmit"))
{
curElement.InvokeMember("click");
}
}
}
here is the whole code. I tried setting the delay with timer thinking because it is reacting too fast but the timer is also not working so im not sure what the problem could be.
the code that doesnt work is suppose to create the avList with 3 counts and choose the value 1. the value 1 represents the In Stock availability of the website.
when running without debugging it seems to completely ignore the code written in the if condition.
thanks

Ok, the issue looks to be with the way you setup your code. You are trying to do things one after the other which is yielding some strange results. It is best to allow the API (WebBrowser) tell you what is going on rather than trying to query it until it is done.
Having a loop to check "are you done yet?" is considered back practice because it blocks your code and occupies the processor with a wasteful wait loop.
What you need to do, is look through the documentation for the WebBrowser API and figure out how the WebBrowser communicates back to the calling class. C# takes a huge advantage of Events and Delgates, so my suggestion is to look to see if there is an event for what you are looking for. A quick search came up with:
http://msdn.microsoft.com/en-us/library/system.windows.forms.webbrowser.ondocumentcompleted.aspx
This is far move manageable approach than to spin a while loop until the condition is met. Let the API inform you when it's done and then you can decide what to do with it. As for your events, here is an example of how the event is wired:
http://msdn.microsoft.com/en-us/library/system.windows.forms.control.onkeydown.aspx
so you do not have to check for them in a loop, eating up processing time.
Also, since your in the .NET world you have access to linq. You don't have to write out your loops in order to find something. For instance:
//Note: I have not tested this code, but this is close to what it should look like
bookCollection.where(x => x.GetAttribute("id").ToString() == "searchTitle")
.ForEach(x => x.SetAttribute("value", entry));
I cannot vouch for how fast this is, but LINQ tends to clean up the logic for looping and searching.
=====================================
If you insist of having your code, the issue arises from
webBrowser1.ReadyState
which is no longer in the "Complete" state. However, your while loop already checks for this condition right above, so you can just remove the IF statement. The reason I told you that you have an iffy while loop is for this exact reason. The enum value is there so that you can query the WebBrowser process while it is still processing. This is useful in multithreaded software. However, my guess is that the flag is flipped to
webBrowser1.ReadyState == WebBrowserReadyState.Complete
right before the page is displayed. That would explain why your while loop picks up on it and exists out. Now, the issue is that it will probably flip the enum to Uninitialized because it is finished loading the page and has disconnected the socket connection. This would put it into the Unintialized state. This API relies on a state machine pattern and the sequence of the states are are probably different from what you think they are. Here is more information about state machine:
Simple state machine example in C#?
I hope this helps!

Client Coding error for chatting application

I'm getting a error in my code
Cross-thread operation not valid:
Control '' accessed from a thread
other than the thread it was created
on.
I don't know why it is happening. Can someone explain this to me?

That is hapening because you are accessing to a control in your Windows Form application from another thread.
Could you share your code?
Let's suppose you are accessing to a TextBox (which name is textBox1):
textBox1.Text = "Modified text"
Instead of doing that, you must do:
MethodInvoker m = () => { textBox1.Text = "Modified text"; };
if (InvokeRequired) {
BeginInvoke(m);
}
else {
m.Invoke();
}
Of course, that was a simple example. You can encapsulate the Invoking part in in a method so you don't repeat the same code over and over. Something like:
public void InvokeSafe(MethodInvoker m) {
if (InvokeRequired) {
BeginInvoke(m);
}
else {
m.Invoke();
}
}
so all you have do to is:
MethodInvoker m = () => { textBox1.Text = "Modified text"; };
InvokeSafe(m);

Common reason is if you are trying to access data available for UI thread from your background thread. Verify that you are not accessing data across threads.
You need to post more details.

The message is quite clear. Cross-thread calls can make the application very unstable thats why it is not valid.
Here is some documentation how to solve this:
http://www.vcskicks.com/cross-thread.php
http://www.dreamincode.net/forums/topic/35616-cross-thread-communication-in-c%23/

c# class - make function or method call and pass control

I'm not sure if my title is really correct. I've looked around and searched but not found anything so please forgive me if my problem has been answered already.
What I would like to do is call a function but not have to come back to the calling line of code. e.g
public static void temp(obj) {
switch (obj.id) {
case "1" :
if(blah) {
obj.id = "2";
temp(obj);
}
break;
case "2" :
obj.response = "done";
break;
}
}
so basically I dont want to eventually come back to my temp(obj) in the first case and fully pass control. Does this make sense, is it even possible and my architecture is all wrong?
Thank you for your time.

Let me see if I understand the question:
You've got a function Foo(), which calls function Bar(). (I wanted to remove the recursion you had in your example for simplicity, please correct me if that was important.) When function Bar() returns, you want control to pass not back to Foo(), but to Foo's caller?
This is probably possible in lower-level languages, like C, by hacking the stack and not placing Foo()'s return address there, so that when Bar() tried to return, it would jump to Foo's caller instead.
However, in C#, no. The call stack is a stack, and control will pass back in order. The only thing you can do would be to put a return statement after each call to Bar().
Edit:
"recursive calls without them being recursive"
How about this:
bool doItAgain = true;
while(doItAgain)
{
doItAgain = false;
// process, with your switch statement or whatever.
if(...)
{
doItAgain = true;
continue; // if necessary, skip any code after this statement. May not be necessary if you have things set up right.
}
}

If this were C++, you could eliminate the break and let the case "1" fall through, but this is not allowed in C# switch statements.
public static void temp(obj) {
if (obj.id == "1") {
obj.id = "2";
temp(obj);
}
if (obj.id == "2")
obj.response = "done";
}
Do you need the recursive call? This code retains your recursive call and sets obj.response to "done" after changing obj.id to "2". However, obj.response is set twice because of the recursive call. What are you trying to do?

I'm not sure what you exactly intend, but it sounds like a callback to me. Here is one possible example:
void DoSome()
{
ThreadPool.QueueUserWorkItem(new WaitCallback(delegate { RunMe(); ReturnTo(); }));
}
void RunMe() { }
void ReturnTo() { }
You start in DoSome() and continue, when RunMe is finished ReturnMe is called.