If condition check in a interruptible function. Is it safe?

[binhnx]

Let start with some examples:

1. (As seen in another topic: '?do=embed' frameborder='0' data-embedContent>> ).

Script copied from that topic

Interrupt function can be any hotkey/event/adlib/callback.

If-check inside interrupted function/script 

; HotKeySet, or any function that can cause script interrupt
HotKeySet("{Delete}", "RemoveSelectedControl")

;...
Dim $InfoAboutControls[4096]
Global $HandleForCurrentControl
;...


While 1
    $msg = GuiGetMsg()
  ;....
    
  ;---Code to process moving a control (drag-n-drop)---
    ; If check in MAIN LOOP (interruptible function).
    If $HandleForCurrentControl > 0 Then;Make sure we have a valid control handle
  ; ***** oops user pressed Delete key and we get pre-empted
  ; ***** user removed the selected control.
  ; ***** Returning from the RemoveSelectedControl function and resuming here:
        GuiCtrlSetPos($InfoAboutControls[$HandleForCurrentControl], $newLeftPosition, $newTopPosition)
    EndIf
WEnd

Func RemoveSelectedControl()
    $HandleForCurrentControl = -1
EndFunc

2. If-check inside interrupt function

Hotkey only.

Flag is set right after if check.

It's possible or not this function print twice or more?

HotKeySet("{Delete}", "_TestHotkey")

Func _TestHotkey()
  Static $bFlag = True
  If ($bFlag) Then 
     ; ***** Right here, user pressed Delete key
     ; ***** bFlag is currently not set
     ; ***** And the script will execute this function twice or more times, instead of just once
     $bFlag = False
     ConsoleWrite("This should be printed only ONCE")
  EndIf
EndFunc

3. Same as 2, but with global flag

The question is: can I rely on if-checking with a flag, to ensure that my script doesn't do any strange things, as describe in the above examples?

Edited October 15, 2014 by binhnx

[Bert]

What is the overall purpose of your script? It may be simpler to post your script and the issue you have.

Edited October 15, 2014 by DarthCookieMonster

[binhnx]

Not a specific script. That is only a general problem, and I ask for a general answer.

Indeed, 3 above examples is details as much as it should. Any line added to that is for nothing but make the topic unfocused.

To provide more details, 

• Details about example 1 can be read in the original topic linked.
• For example 2 and 3: As you see, my script only allow _TestHotkey() function to execute exactly once. But since AutoIt script can be interrupted and reentrant, it's probably that function be executed twice or more, if user presses "Delete" key right after the if-check line is executed. So, I need an assurance that AutoIt "had some mechanism" to play with it, like a Critical Section as describe at the linked topic.

[BrewManNH]

There is almost no possibility of that function running twice if you clear the hotkey/adlib function used to call it as the very first line of the function.

HotKeySet("{Delete}", "_TestHotkey")

Func _TestHotkey()
  HotKeySet("{Delete}")
  Static $bFlag = True
  If ($bFlag) Then 
     ; ***** Right here, user pressed Delete key
     ; ***** bFlag is currently not set
     ; ***** And the script will execute this function twice or more times, instead of just once
     $bFlag = False
     ConsoleWrite("This should be printed only ONCE")
  EndIf
EndFunc

If you wanted the HotKey to be active again, you'd need to set it again somewhere else in the script. AdlibUnRegister would work the same way.

[jdelaney]

Or:

$bFlag = True
HotKeySet("{Delete}", "_TestHotkey")

Func _TestHotkey()
  If $bFlag Then 
     ; ***** Right here, user pressed Delete key
     ; ***** bFlag is currently not set
     ; ***** And the script will execute this function twice or more times, instead of just once
     $bFlag = False
     ConsoleWrite("This should be printed only ONCE")
  EndIf
EndFunc

While True
WEnd

Edited October 15, 2014 by jdelaney

[binhnx]

@BrewmanNH: yeah, in your case, if Delete is pressed right at the function begining, before the HotKeySet line, so what will happen?

In general, it also very very low probability, but i need to an exactly zero. 

Indeed, with Hotkey, if a line is the smallest element in AutoIt, so interrupt a line never can occur, so another trick will be better:

Func _TestHotKey()
 Static $nCounter = 0
 $nCounter += 1
 If ($nCounter = 1) Then
  ;Do everything you want
 EndIf
 $nCounter -= 1
EndFunc

It guarantee that the function execute exactly once (at the same time). But this method cannot be used with event or adlib since all that is queued, not interruped & reentrant.

@jdelaney: It's exactly my example 3. It's still unsafe at all, unless a dev state that it's safe!

A side note: The set flag statement is right after the check statement. I wonder AutoIt has some guard around it, or it's still simply a race-condition problem.

Edited October 15, 2014 by binhnx

[BrewManNH]

There's probably a .000000000000000000000000001% chance that someone could hit the same key twice in the time it takes to get to that line. There's no such thing as exactly zero in computers, you are NEVER going to achieve that, especially in an interpreted language.

[binhnx]

@BrewmanNH.

No, as seen in the linked topic: '?do=embed' frameborder='0' data-embedContent>>

If a Critical Section (or any other guards) is implemented, it should be exactly zero!

The linked topic is provide a little information so I do not know it is implemented or not, so I open this topic to ask.

A side note: Computing is all about zero and one, isn't it?

[BrewManNH]

We're talking about timing, not numbers. Also, if you had read the first response to that nearly 10 year old thread, the answer given is exactly what I proposed.

[binhnx]

Yeah, just kidding

I've read, and notice that, but after search along the forum, no other topic describe that problem, so I haven't know about its state yet.

In computing, many method is implemented to ensure that everything is done right. In a general programming language, also count interpreted language, such as Python or PHP also implemented that, using a lock before the check and the problem solved.

Is AutoIt (internally) did that?

Edit: Maybe I mis-understood what the Overlord said? Did he said that the guard function is totally imlemented? Or totally ignored? Or he said that the guard function is implemented around the disable Hotkey/Adlib/OnEvent function? 

Edited October 15, 2014 by binhnx

[BrewManNH]

There is no guard function, you'd have to program that yourself, and it's all about disabling the hotkey or adlib as soon as you enter the function. Either by calling another function to clear it, or by implementing it inside the function being called. You're worrying over less than nothing in this thread, the function won't be called twice because you can't press the hotkey that fast, it's as close to zero time as is possible on a computer and using an interpreted language. If you need something quicker than almost instantaneous, you need to use another language.

[binhnx]

Thank you for your patience, but it seems not much logic since the OP of the linked topic can disable Adlib/Hotkey/OnEvent right before check statement and re-enable it after go out of work section, without using CriticalSection guard, but still ensure script works right.

And, with the behavior of AutoIt when processing Event/HotKey/Adlib, using CriticalSection inside a script is a bad idea, because it:

• Have no effect when using inside Event/Adlib function, since these kind result in a queued function call, so next EnterCriticalSection always called after last LeaveCriticalSection is called => no effect at all
• Resulted in dead-lock when using with Hotkey, think about Hotkey is pressed right after called to EnterCriticalSection, and it resulted in wait for a not-released CriticalSection, also, to release it, the function should be returned from the later Hotkey function, but it's stuck since the later one is stuck in EnterCriticalSection call. Using multipleCriticalSection (using local variable so we have one with each called function) is out of concept because it cannot guarantee anything if we use it like that.
• Use inside a normal function/mail script: has not much logic, since a normal disable function will solve the problem.

Furthermore, writing using a different language is not an option. You may think I mad, it's OK. Maybe I somewhat like AutoIt and I want to write in AutoIt than using a different language.

But this time, the reason makes me stick with AutoIt is I'm writing a program that use AutoIt as underlying rendering program (Yes, a form designer, AutoIt lacks a good designer. First, I need a native renderer, instead of using another language to do it, as Koda used Delphi. This will provide a better experiencement to user, since the designer form is exactly visually identified with the result form. Second, The FormBuilder Beta found in the forum - which is written entirely in AutoIt - is elegance, but too much crashable bug. So I decided to write a new one)

Edited October 15, 2014 by binhnx

[BrewManNH]

 

And, with the behavior of AutoIt when processing Event/HotKey/Adlib, using CriticalSection inside a script is a bad idea, because it:

How do you know that? Have you ever run into a problem with using what I posted? Not some theoretical "what-if" scenario, I mean real world examples of where a hotkey can be pressed quicker than it takes to disable it in the function that's called by it. Have you ever encountered a deadlock condition from using a hotkey in the way I demonstrated? My guess would be no to all questions, because the probability of it happening is extremely small.

If you think you can show a way to do it, please post a script that demonstrates it.

[binhnx]

Have you ever seen any real-world-100%-will-occur-race-condition?

The answer is 'absolutely NO', because this is very very rare to occur, but every one can ensure that, at a random (not-so) beautiful day, your application will crash stupidly because a stupid bug. It's not acceptable with a programmer, but may be acceptable with a scripter/ automater. 

It's not speed problem. It's timing problem.

It's not about how many small. It's YES or NO

[binhnx]

Maybe I asked at wrong forum region.

Anyone may have a look at 

and give me some advice? Thank you very much!

[JLogan3o13]

You have a thread going, which is getting replies (even if not fast enough for you). Please don't double post

[Jos]

Merged, now please stick to one topic.

Jos

[binhnx]

I think, I posted in the wrong thread. all I need is a answer by a developer, who can easily say that yes or no. I'm tired of explaining anything about my question.

Should I delete the thread and re-post?

Edited October 15, 2014 by binhnx

[JLogan3o13]

Not if you want a long and healthy stay on the forum

If people are still asking for clarification, maybe you should take that as a clue that you're not explaining yourself very well.

[binhnx]

So, honestly, may you spend some time to read my post and give me some point, what do I need to answer, to get the answer for me?

Edited October 15, 2014 by binhnx