[C# Tip] Illegal Cross-Thread Operations

Buzzerbee · Before February 2015

Do you run into this exception often?

Don't fret; invoke!

If you use winforms often, you may see this exception while trying to change properties of your controls.

For example, I have my "Connect!" button change to "Disconnect" whenever the bot is connected to a world, that way the user knows that they are now connected, and can disconnect by pressing the button again.

However, when I do this, an exception would be thrown because the control I tried to access "crossed" threads. In other words, it's a no-no.

Some people, when they see this exception, try to take the easy way out and change the bool for checking for these illegal operations.

CheckForIllegalCrossThreadCalls = false;

However, this is VERY dangerous. When multithreading, you are basically telling your program to ignore anything wrong rather than fixing the problem. This could cause bot crashes!

There IS a better solution!

Use invocation!

Basically, when you invoke, you're telling your program to search further into your control, until it reaches a parent that it can safely handle.

Here's how to use it!

Instead of

connect.Text = "Disconnect";

I would simply use:

this.Invoke((MethodInvoker)delegate {     connect.Text = "Disconnect"; });

And the exception will no longer be thrown, and the code is safely handled.

Always do this next time you are working with controls!

(If there is anything wrong with this method, please let me know.)

Last edited by BuzzerBee (Jun 18 2014 1:20:04 pm)

JadElClemens, SirJosh3917

Hexagon · Before February 2015

This is definitely definitely useful. If I had this a few weeks ago, would have saved me a few hours of searching and debugging.

TiKen · Before February 2015

I personally used a custom class derived from INotifyPropertyChanged with bindings

I can give more details if anyone wants =P

Last edited by tikenalpha (Jun 18 2014 2:25:37 pm)

Cyral · Before February 2015

You could also extend this into a handy extension method, there are many ways but this is my favorite:

public static void Invoke<T>(this T control, Action<T> action) where T : Control {     if (control.InvokeRequired)         control.TopLevelControl.Invoke(action);     else         action(control); }

Which you can simply use with:

connect.Invoke(c => c.Text = "Disconnect");

Last edited by Cyral (Jun 30 2014 8:36:16 am)

XxAtillaxX · Before February 2015

It's quite stupid to invoke one line of code, the same way it's stupid to put try/catch on everything.
Otherwise, it might be useful to implement, but not in ALL cases.

Last edited by XxAtillaxX (Jun 30 2014 5:14:14 pm)

2015-05-28 06:21:06

We have to let everyone know this.

What's so dangerous about it anyway eh?

Xfrogman43 · 2015-05-28 08:18:41

Buzzerbee wrote:

However, this is VERY dangerous. When multithreading, you are basically telling your program to ignore anything wrong rather than fixing the problem. This could cause bot crashes!

This is why It's dangerous.

2015-05-28 08:46:00

What kind of problems?

den3107 · 2015-05-28 10:15:37

A variable can be written to by 2 seperate threads. I think that's the most common problem (at least was for me).

Tomahawk · 2015-05-28 21:09:36

I seem to recall that the shortest code required to complete a task is the best, unless it proves to be harmful in some way.
Using "CheckForIllegalCrossThreadCalls = false;" and screwing with threads hasn't done anything harmful to me in 3 years of coding, so there's no incentive to invoke that extra effort (ha).

Let's not make the bot motto: "Per aspera ad astra".

You're also much too vague on why and in which situations it's "very dangerous".

realmaster42

BuzzerBee · 2015-05-30 22:37:10

I was not vague. I just didn't give copious examples.

The main problem is it can cause crashes. That should be a good enough reason alone not to use it.

Here's a stackoverflow answer as to why it can be harmful:

http://stackoverflow.com/a/2587977

darkblades · 2015-06-01 17:29:04

checkforillegalcrossthreadcalls is useless when it is stand-alone and it only works for debugging and invoking is 2903293x more better because it removes the random crashiness

I'm getting an exception of crossthread on "form1" not controls and my options are Ok or quit. how to solve.

I'm also getting exceptions on accessing disposed objects by using your invoke method when my app closes

realmaster42 · 2015-06-01 19:28:07

My bot uses CheckForIllegalCrossThreadCells = false and it never crashes outside the debugger.

everyone downloading the .exe doesn't crash...
You know what crashes? Missing references.

realmaster42 · 2015-06-01 19:30:10

darkblades wrote:

checkforillegalcrossthreadcalls is useless when it is stand-alone and it only works for debugging and invoking is 2903293x more better because it removes the random crashiness
I'm getting an exception of crossthread on "form1" not controls and my options are Ok or quit. how to solve.
I'm also getting exceptions on accessing disposed objects by using your invoke method when my app closes

use CheckForIllegalCrossThreadCells = false;

Remove all the useless invokes. (Why the **** do people even spam it on the bot)
'Random crashinies' Then or missing references or ur code is wrong
'Only on debug' my bot is working on Release and the official .exe

Dude, seriously, debug it from a file with cloned references, not in project directory...

den3107 · 2015-06-01 19:56:21

marcoantonimsantos wrote:

darkblades wrote:
checkforillegalcrossthreadcalls is useless when it is stand-alone and it only works for debugging and invoking is 2903293x more better because it removes the random crashiness
I'm getting an exception of crossthread on "form1" not controls and my options are Ok or quit. how to solve.
I'm also getting exceptions on accessing disposed objects by using your invoke method when my app closes
use CheckForIllegalCrossThreadCells = false;
Remove all the useless invokes. (Why the **** do people even spam it on the bot)
'Random crashinies' Then or missing references or ur code is wrong
'Only on debug' my bot is working on Release and the official .exe
Dude, seriously, debug it from a file with cloned references, not in project directory...

Personally crashes thanks to this.
My bot has a little loop going on in one of the threats, by using your 'oh-so-much-better' method, this causes the bot to crash occasionally because a single variable is being accessed by two separate threads at the same time.

Using the better, safer way (personally use a bit different method that Bee does, but it's not a pretty one-liner), I don't have that problem anymore.

You bot might too crash because of this, but since I had a loop going on, the chances of it happening on me were a lot bigger.

BuzzerBee · 2015-06-01 20:41:15

marcoantonimsantos, please don't argue about this. You are wrong. Goodbye.

DarkDragon4900, ewoke

realmaster42 · 2015-06-01 20:47:03

den3107 wrote:

marcoantonimsantos wrote:
darkblades wrote:
checkforillegalcrossthreadcalls is useless when it is stand-alone and it only works for debugging and invoking is 2903293x more better because it removes the random crashiness
I'm getting an exception of crossthread on "form1" not controls and my options are Ok or quit. how to solve.
I'm also getting exceptions on accessing disposed objects by using your invoke method when my app closes
use CheckForIllegalCrossThreadCells = false;
Remove all the useless invokes. (Why the **** do people even spam it on the bot)
'Random crashinies' Then or missing references or ur code is wrong
'Only on debug' my bot is working on Release and the official .exe
Dude, seriously, debug it from a file with cloned references, not in project directory...
Personally crashes thanks to this.
My bot has a little loop going on in one of the threats, by using your 'oh-so-much-better' method, this causes the bot to crash occasionally because a single variable is being accessed by two separate threads at the same time.
Using the better, safer way (personally use a bit different method that Bee does, but it's not a pretty one-liner), I don't have that problem anymore.
You bot might too crash because of this, but since I had a loop going on, the chances of it happening on me were a lot bigger.

are you using Thread.Sleep? Those are important in Loops.

TiKen · 2015-06-01 22:59:44

marcosantonimsantos wrote:

are you using Thread.Sleep? Those are important in Loops.

Wait... what?! If you are relying on Thread.Sleep to save you from a crash, you're in deep troubles my friend.

madiik, Raon, BuzzerBee, Xfrogman43, lrussell, DarkDragon4900

realmaster42 · 2015-06-01 23:10:32

TiKen wrote:

marcosantonimsantos wrote:
are you using Thread.Sleep? Those are important in Loops.
Wait... what?! If you are relying on Thread.Sleep to save you from a crash, you're in deep troubles my friend.

Actually, I'm talking about loops.
Not using Delay or Thread.Sleep in those will give StackOverFlow, crashing his bot, and here is where he is doing it wrong...

TiKen · 2015-06-01 23:21:04

marcoantonimsantos wrote:

TiKen wrote:
marcosantonimsantos wrote:
are you using Thread.Sleep? Those are important in Loops.
Wait... what?! If you are relying on Thread.Sleep to save you from a crash, you're in deep troubles my friend.
Actually, I'm talking about loops.
Not using Delay or Thread.Sleep in those will give StackOverFlow, crashing his bot, and here is where he is doing it wrong...

Illegal cross thread calls and stack overflows are two completely separated things (even if the second can result from the first one) O-o
A stack overflow has no reason to show up in ANY loop if boundaries are well set. The only reason I see here to a stack overflow showing in your loops is if a thread changes the size of an array/list while another one is using it (I made the hypothesis you know how to define boundaries to avoid a basic stack overflow).

tl;dr: You just prove yourself wrong. DO NO CREATE ILLEGAL CROSS THREAD CALLS

Edit: Stack overflows can also happen in recursive functions where boundaries are ill-set, or if there is simply to many calls. But I don't think it's what is showing up here.

den3107 · 2015-06-02 00:20:02

marcoantonimsantos wrote:

▼someqoutes
den3107 wrote:
marcoantonimsantos wrote:
darkblades wrote:
checkforillegalcrossthreadcalls is useless when it is stand-alone and it only works for debugging and invoking is 2903293x more better because it removes the random crashiness
I'm getting an exception of crossthread on "form1" not controls and my options are Ok or quit. how to solve.
I'm also getting exceptions on accessing disposed objects by using your invoke method when my app closes
use CheckForIllegalCrossThreadCells = false;
Remove all the useless invokes. (Why the **** do people even spam it on the bot)
'Random crashinies' Then or missing references or ur code is wrong
'Only on debug' my bot is working on Release and the official .exe
Dude, seriously, debug it from a file with cloned references, not in project directory...
Personally crashes thanks to this.
My bot has a little loop going on in one of the threats, by using your 'oh-so-much-better' method, this causes the bot to crash occasionally because a single variable is being accessed by two separate threads at the same time.
Using the better, safer way (personally use a bit different method that Bee does, but it's not a pretty one-liner), I don't have that problem anymore.
You bot might too crash because of this, but since I had a loop going on, the chances of it happening on me were a lot bigger.
are you using Thread.Sleep? Those are important in Loops.

I am using some form of delay for the loop, yes, but the problem is, that a quick loop has a higher chance to get a variable to be accessed from 2 separate threads is much higher than when using one-time operations.
Yet still, just like in your bot, it's perfectly possible that it will still happen and your bot will crash.
And people won't be happy to hear it's something you can't/won't fix, gives you bad cred.

Xfrogman43 · 2015-06-02 01:34:56

Just because your bot doesn't crash, doesn't mean it won't.

realmaster42 · 2015-06-02 08:18:13

den3107 wrote:

marcoantonimsantos wrote:
▼someqoutes
den3107 wrote:
marcoantonimsantos wrote:
darkblades wrote:
checkforillegalcrossthreadcalls is useless when it is stand-alone and it only works for debugging and invoking is 2903293x more better because it removes the random crashiness
I'm getting an exception of crossthread on "form1" not controls and my options are Ok or quit. how to solve.
I'm also getting exceptions on accessing disposed objects by using your invoke method when my app closes
use CheckForIllegalCrossThreadCells = false;
Remove all the useless invokes. (Why the **** do people even spam it on the bot)
'Random crashinies' Then or missing references or ur code is wrong
'Only on debug' my bot is working on Release and the official .exe
Dude, seriously, debug it from a file with cloned references, not in project directory...
Personally crashes thanks to this.
My bot has a little loop going on in one of the threats, by using your 'oh-so-much-better' method, this causes the bot to crash occasionally because a single variable is being accessed by two separate threads at the same time.
Using the better, safer way (personally use a bit different method that Bee does, but it's not a pretty one-liner), I don't have that problem anymore.
You bot might too crash because of this, but since I had a loop going on, the chances of it happening on me were a lot bigger.
are you using Thread.Sleep? Those are important in Loops.
I am using some form of delay for the loop, yes, but the problem is, that a quick loop has a higher chance to get a variable to be accessed from 2 separate threads is much higher than when using one-time operations.
Yet still, just like in your bot, it's perfectly possible that it will still happen and your bot will crash.
And people won't be happy to hear it's something you can't/won't fix, gives you bad cred.

Try using timers

den3107 · 2015-06-02 12:12:46

marcoantonimsantos wrote:

▼someqoutes
den3107 wrote:
marcoantonimsantos wrote:
den3107 wrote:
marcoantonimsantos wrote:
use CheckForIllegalCrossThreadCells = false;
Remove all the useless invokes. (Why the **** do people even spam it on the bot)
'Random crashinies' Then or missing references or ur code is wrong
'Only on debug' my bot is working on Release and the official .exe
Dude, seriously, debug it from a file with cloned references, not in project directory...
Personally crashes thanks to this.
My bot has a little loop going on in one of the threats, by using your 'oh-so-much-better' method, this causes the bot to crash occasionally because a single variable is being accessed by two separate threads at the same time.
Using the better, safer way (personally use a bit different method that Bee does, but it's not a pretty one-liner), I don't have that problem anymore.
You bot might too crash because of this, but since I had a loop going on, the chances of it happening on me were a lot bigger.
are you using Thread.Sleep? Those are important in Loops.
I am using some form of delay for the loop, yes, but the problem is, that a quick loop has a higher chance to get a variable to be accessed from 2 separate threads is much higher than when using one-time operations.
Yet still, just like in your bot, it's perfectly possible that it will still happen and your bot will crash.
And people won't be happy to hear it's something you can't/won't fix, gives you bad cred.
Try using timers

As I said, I'm already using some form of delay... And as I also said, the delay isn't causing the crashes... Just nvm...

madiik · 2015-06-02 12:48:56

So far I have just kept creating backgroundWorkers with events in lambda expression. It's quite easy and readable.

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#1 Before February 2015

[C# Tip] Illegal Cross-Thread Operations

#2 Before February 2015

Re: [C# Tip] Illegal Cross-Thread Operations

#3 Before February 2015

Re: [C# Tip] Illegal Cross-Thread Operations

#4 Before February 2015

Re: [C# Tip] Illegal Cross-Thread Operations

#5 Before February 2015

Re: [C# Tip] Illegal Cross-Thread Operations

#6 2015-05-28 06:21:06

Re: [C# Tip] Illegal Cross-Thread Operations

#7 2015-05-28 08:18:41

Re: [C# Tip] Illegal Cross-Thread Operations

#8 2015-05-28 08:46:00

Re: [C# Tip] Illegal Cross-Thread Operations

#9 2015-05-28 10:15:37

Re: [C# Tip] Illegal Cross-Thread Operations

#10 2015-05-28 21:09:36, last edited by Tomahawk (2015-05-28 21:10:43)

Re: [C# Tip] Illegal Cross-Thread Operations

#11 2015-05-30 22:37:10

Re: [C# Tip] Illegal Cross-Thread Operations

#12 2015-06-01 17:29:04, last edited by darkblades (2015-06-01 17:32:17)

Re: [C# Tip] Illegal Cross-Thread Operations

#13 2015-06-01 19:28:07

Re: [C# Tip] Illegal Cross-Thread Operations

#14 2015-06-01 19:30:10, last edited by realmaster42 (2015-06-01 19:30:41)

Re: [C# Tip] Illegal Cross-Thread Operations

#15 2015-06-01 19:56:21

Re: [C# Tip] Illegal Cross-Thread Operations

#16 2015-06-01 20:41:15

Re: [C# Tip] Illegal Cross-Thread Operations

#17 2015-06-01 20:47:03

Re: [C# Tip] Illegal Cross-Thread Operations

#18 2015-06-01 22:59:44

Re: [C# Tip] Illegal Cross-Thread Operations

#19 2015-06-01 23:10:32

Re: [C# Tip] Illegal Cross-Thread Operations

#20 2015-06-01 23:21:04, last edited by TiKen (2015-06-01 23:23:08)

Re: [C# Tip] Illegal Cross-Thread Operations

#21 2015-06-02 00:20:02

Re: [C# Tip] Illegal Cross-Thread Operations

#22 2015-06-02 01:34:56

Re: [C# Tip] Illegal Cross-Thread Operations

#23 2015-06-02 08:18:13

Re: [C# Tip] Illegal Cross-Thread Operations

#24 2015-06-02 12:12:46

Re: [C# Tip] Illegal Cross-Thread Operations

#25 2015-06-02 12:48:56

Re: [C# Tip] Illegal Cross-Thread Operations

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