_Singleton Generates Multiple Objects!

[TheDcoder]

Hello , Please look at the code below:

; This is not the real script that I use for my project!!! This decoy script helps you understand better ;)

#include "Misc.au3"

Global $sProgramIdentifier

Func Test($sIdentifier)
    $sIdentifier = $sProgramIdentifier
    Switch _Singleton($sProgramIdentifier, 1)
        Case 0
            MsgBox(64, "Testing, Testing", "Its working!!")
        Case Else
            MsgBox(64, "Testing, Testing", "Its not working!!")
    EndSwitch
EndFunc

Test("Lick the lemon")

Save this to a file and run it, you will get a MsgBox telling "Its not working!!"

Again, Run the script a second-time without closing the first MsgBox and you will again get a MsgBox telling the same thing!! This was not supposed to happen

How can I get the MsgBox telling that it works ?

Thanks In Advance, TD

[Danp2]

You are overwriting the passed parameter with the global variable,  which I suspect is the opposite of what you intended. 

[Melba23]

TheDcoder,

And referencing this thread, you are generating multiple instances, not multiple objects.

M23

[TheDcoder]

@Danp2 Overwritten or not, but the content does not change, does it?

@Melba23 I don't quite understand the difference "instances" & "objects" here, please explain

TD

[Melba23]

TheDcoder,

Multiple instances are where the same app is running several times at the same time. You can see this with SciTE using the check.if.already.open option - if not set (which is the default SciTE4AutoIt3 setting) each file is opened in a new tab; if set each file is opened in a new instance of SciTE. Give it a try and see - but add the line to your User Properties file so you can delete it once you have tested.

Objects are something entirely different - and I suggest you do what >JohnOne suggested and do some Google research for yourself. You might want to start here.

M23

[TheDcoder]

@Melba23 I know what instances are, but in this case _singleton should return 0 because there are multiple instances (like in the example for _Singleton). I wanna know why _Singleton is retuning multiple mutex(es) instead of 0

TD

P.S Thanks for the wiki link

Edited April 5, 2015 by TheDcoder

[Melba23]

TheDcoder,

_Singleton depends on you passing something which can create a mutex object which is then used to flag whether it is currently in use. In the script you posted, the string used by _Singleton to generate the mutex is empty - which from my limited knowledge means that the whole system falls over. If you assign a proper string to the mutex like this:

Global $sProgramIdentifier = "fred"

then the mutex object is successfully created and the second instance does indeed return "Its working!!".

And anyway, why are you using a function parameter which you immediately reassign within the function? It makes no sense at all.

M23

Edited April 5, 2015 by Melba23
Fixed tags

[TheDcoder]

And anyway, why are you using a function parameter which you immediately reassign within the function? It makes no sense at all.

You will get to know it soon

 

$sIdentifier = $sProgramIdentifier

Doesn't this line assign the variable a value?

TD

[Melba23]

TheDcoder,

Indeed it does - but the question is why you are immediately reassigning a function parameter to a Global variable. You use parameters to pass specific values to a function, or to assign default values if no parameter is passed. If you want to use a Global variable inside a function, then there is no point in doing what you did - just use the variable directly.

M23

[TheDcoder]

Thanks Melba!

This code works:

; NOTE: Removed line no.6 & modified line no.7 in the previous code :)

#include "Misc.au3"

Func Test($sIdentifier)
    Switch _Singleton($sIdentifier, 1)
        Case 0
            MsgBox(64, "Testing, Testing", "Its working!!")
        Case Else
            MsgBox(64, "Testing, Testing", "Its not working!!")
    EndSwitch
EndFunc

Test("Lick the lemon")

TD

P.S I still wonder why my first code doesn't work

[Melba23]

TheDecoder,

 

I still wonder why my first code doesn't work

I thought I had already explained that.

You were resetting the function parameter which you use to create the mutex to the value of an undefined Global variable - mutexes need a string to work, so passing an empty string meant that the function would fail.

M23

[TheDcoder]

@Melba23 Erm.... Why does this line:

$sIdentifier = $sProgramIdentifier

Not pass the string??

[iamtheky]

It does pass it and it is empty, lets try this a third time "Empty strings dont work!"  

Global $sProgramIdentifier
 
$sProgramId2 = ""
 
_test($sProgramIdentifier , $sProgramId2)
 
 
Func _test($sParam1 , $sParam2)
 
If $sProgramId2 == $sProgramIdentifier Then msgbox (0, '' , "those are the same thing and neither will work")
 
EndFunc
 
 

[Danp2]

@Melba23 Erm.... Why does this line:

$sIdentifier = $sProgramIdentifier

Not pass the string??

 

You are overwriting the passed parameter with the global variable,  which I suspect is the opposite of what you intended. 

 

This is what I tried to point out in my initial post. Let's break this down into simple steps:

• You declare a global variable named $sProgramIdentifier, but never assign it a value
• You call the function Test with the parameter "Lick the lemon"
• The string gets stored into the variable $sIdentifier
• You overwrite the value of $sIdentifier ("Lick the lemon") with the value of $sProgramIdentifier (Undefined)

Can you explain the intended purpose of the global variable? Is it supposed to contain the most recent value passed to the Test function? 

[TheDcoder]

• You overwrite the value of $sIdentifier ("Lick the lemon") with the value of $sProgramIdentifier (Undefined)

Sorry all, What I thought is:

$sIdentifier = $sProgramIdentifier

  ---------------->  = ----------------->

But I forgot that

<--------------- = <--------------------

Thanks, TD

Edit: Completed the post (pressed the submit button mistakenly)

Edit 2: Comma

Edited April 6, 2015 by TheDcoder