While-WEnd Question

[michaelslamet]

My script run by many users on a network drive. Before it run a particular function,
the script need to make sure that this function is only run only 1 time in the last 200 miliseconds.

Example:
Script at PC-A run this function at hour 12:00:05.190

then
Script at PC-B can not run this function before 12:00:05.390

So when there is a request, it should sleep until it pass the 200ms.

So I keep a record "which PC run this function and when" into a MySQL database on a server.
No problem on this part.

I also have no problem on finding a milisecond different between current time and last record
on the database.

My only problem is sometime my routine that "sleep until 200ms passed" fail.
Example, this is a database record:

1--> 12:00:05.190
2--> 12:00:05.590
3--> 12:00:05.690

As we can see, between second and third row, the delay is only 100ms.
Third row/record is created because my routine think it's now pass the 200ms delay
because IT'S USING FIRST RECORD AS REFERENCE! What it dont know is while it's sleeping
waiting the 200ms to pass, another PC run this function (so the second record is created).

This is my code:

SleepUntilCanAccess (200)
Run_this_special_function_that_will_error_if_accessed_more_than_once_in_200_ms()      ; only need few miliseconds for this function to finish
WriteLogToDatabase()
SleepUntilCanAccess (200)

Func SleepUntilCanAccess ($ShouldPassHowManyMiliSecs_Param = 200)
    Local $current_time_local, $last_time_in_database
    Local $date_diff_local
    Local $tmp = 0

    While $tmp < $ShouldPassHowManyMiliSecs_Param
        $current_time_local = StringSplit(@YEAR & ":" & @MON & ":" & @MDAY & ":" & @HOUR & ":" & @MIN & ":" & @SEC & "." & @MSEC, ":")
        _ArrayDelete($current_time_local, 0)                ; delete first element of the array

        $last_time_in_database_local = StringSplit(ReadLastDateFromLogDatabase(), ":")
        _ArrayDelete($last_time_in_database_local, 0)        ; delete first element of the array

        $date_diff_local = _DateDiff_2($last_time_in_database_local, $current_time_local)
        If $date_diff_local[0] > 0 OR $date_diff_local[1] > 0 OR $date_diff_local[2] > 0 OR $date_diff_local[3] > 0 OR $date_diff_local[4] > 0 Then     ; if date_diff return more than 1 min
            ExitLoop
        Else
            $tmp = $date_diff_local[5] * 1000                ; convert to milisecond
            Sleep($ShouldPassHowManyMiliSecs_Param)
        EndIf
    WEnd

    Return
EndFunc

My only thinking for now is before exit the routine, it should check if the reference is THE LAST RECORD?

Please advice me. Thanks you

Edited December 16, 2013 by michaelslamet

[BugFix]

Don't use sleep to determine differences between times. Use better Timer.

[michaelslamet]

Don't use sleep to determine differences between times. Use better Timer.

 

How can I use this in my case?

[BugFix]

Try this:

Func SleepUntilCanAccess ($ShouldPassHowManyMiliSecs_Param = 200)
    ; ...
    $timer = TimerInit()
    While TimerDiff($timer) < $ShouldPassHowManyMiliSecs_Param
        ; ...
        ; ...
    WEnd
    ; ...
EndFunc

[michaelslamet]

Thank you, BugFix

I'm gonna to try it, but I cant see how that can make much difference (?)

[AutID]

I understand nothing from you example. And you have imaginary functions thats dont allow us to test it.
If you want to sleep for 200 miliseconds this will work for you.

Local $timer = TimerInit()
Local $time = _SleepUntilCanAccess(200)
;ConsoleWrite($time & @LF) Comment out these 2 lines if you want to see the time in miliseconds
Func _SleepUntilCanAccess($SleepTime)
 Do
  Local $r = Round(TimerDiff($timer), 1)
  Sleep(10)
 Until $r > $SleepTime
 ;Return $r Comment out these 2 lines if you want to see the time in miliseconds
EndFunc

Comment out the 2 lines if you want to return the miliseconds.
Then you can use your imaginary functions to compare the last time with the time passed returned from this function.

Edited December 16, 2013 by AutID

[guinness]

Surely $timer should be declared as Global and not Local. I know people will tell me but Local outside of a function is Global, but I see this as being a bug of some sorts.

[AutID]

Surely $timer should be declared as Global and not Local. I know people will tell me but Local outside of a function is Global, but I see this as being a bug of some sorts.

Now that you mention it i have ran to that problem as well. And since local outside a function is global then why not declare it as global directly?!?!

Didn't think about it... Good point.

[markyrocks]

My only thought is that what if more than one pc attempts to run script almost simultaneously? Seems they would both be using the previous log entry but would return times within 200 milliseconds of each other? I could be completely wrong but it's an interesting thought.

[JohnOne]

How exactly are your scripts communicating?

[michaelslamet]

How exactly are your scripts communicating?

 

They are not communicating each others. They only read the last record on the MySQL database server before call that particular function to make sure that function is only called (by any scripts) once in 200ms.

Anyway, I think I can use this, but I need to test it tommorow at office. Below I make sure that the reference record has not been change. What do you think?

SleepUntilCanAccess (200)
Run_this_special_function_that_will_error_if_accessed_more_than_once_in_200_ms()      ; only need few miliseconds for this function to finish
WriteLogToDatabase()
SleepUntilCanAccess (200)

Func SleepUntilCanAccess ($ShouldPassHowManyMiliSecs_Param = 200)
    Local $current_time_local, $last_time_in_database
    Local $date_diff_local
    Local $tmp = 0

    While 1
        $current_time_local = StringSplit(@YEAR & ":" & @MON & ":" & @MDAY & ":" & @HOUR & ":" & @MIN & ":" & @SEC & "." & @MSEC, ":")
        _ArrayDelete($current_time_local, 0)                ; delete first element of the array

        $last_log = ReadLastDateFromLogDatabase()
        $last_time_in_database_local = StringSplit($last_log, ":")
        _ArrayDelete($last_time_in_database_local, 0)        ; delete first element of the array

        $date_diff_local = _DateDiff_2($last_time_in_database_local, $current_time_local)
        If ($date_diff_local[0] > 0 OR $date_diff_local[1] > 0 OR $date_diff_local[2] > 0 OR $date_diff_local[3] > 0 OR $date_diff_local[4] > 0) AND (ReadLastDateFromLogDatabase() = $last_log)  Then    ; ; if date_diff return more than 1 min
            ExitLoop
        Else
            $tmp = $date_diff_local[5] * 1000
            If $tmp > $ShouldPassHowManyMiliSecs_Param AND ReadLastDateFromLogDatabase() = $last_log Then
                Return
            Else
                $tmp = 0
            EndIf
        EndIf
    WEnd

    Return
EndFunc

[michaelslamet]

My only thought is that what if more than one pc attempts to run script almost simultaneously? Seems they would both be using the previous log entry but would return times within 200 milliseconds of each other? I could be completely wrong but it's an interesting thought.

 

In fact, that is what currently happened: more than one pc attempts to run the script simultaneously. But this particular function is not called everytime the script run. I just called when user click a particular button.

[markyrocks]

I'm almost thinking that if the function your referring to was saved on a separate .au3 file then you could just check to see if that process is running. If it is then wait till it doesn't exist plus 200ms.

[JohnOne]

They are not communicating each others. They only read the last record on the MySQL database server before call that particular function to make sure that function is only called (by any scripts) once in 200ms.

 

The problem here is that one script does not know if another is accessing the database.

You could and probably will have multiple scripts accessing it at the same time.

2, 3 or 200 scripts check the database all withing 1 millisecond of each other, they see it has not been accessed for 200ms, they all access.

With your current thinking you might get 2 scripts to obey your rules, 3 you're pushing your luck any more, you don't have a chance.

I'd advise you devise a solution server side.

 

[BrewManNH]

Can't you lock the tables while one client is accessing it, then unlock it when it's done?

[michaelslamet]

The problem here is that one script does not know if another is accessing the database.

You could and probably will have multiple scripts accessing it at the same time.

2, 3 or 200 scripts check the database all withing 1 millisecond of each other, they see it has not been accessed for 200ms, they all access.

With your current thinking you might get 2 scripts to obey your rules, 3 you're pushing your luck any more, you don't have a chance.

I'd advise you devise a solution server side.

 

Yes, you're correct, I never think about this before By "server side solution" you mean the MySQL server?

[michaelslamet]

Can't you lock the tables while one client is accessing it, then unlock it when it's done?

 

Hey, this is a interesting idea! I have no idea now how to implement this and how is the logic, but I think this is one of the good solution!

[michaelslamet]

I'm almost thinking that if the function your referring to was saved on a separate .au3 file then you could just check to see if that process is running. If it is then wait till it doesn't exist plus 200ms.

 

No, it is not saved on a separate .au3 file and I dont think this is the issue

[JohnOne]

If you can and do lock the table until one query is completed, alone, you could wind up with some clients getting greedy access while others get none or little.

Probably need a queue control script on the server machine.

[michaelslamet]

If you can and do lock the table until one query is completed, alone, you could wind up with some clients getting greedy access while others get none or little.

Probably need a queue control script on the server machine.

 

Could you please explain more detail about the "queue control script on the server machine"? Which server? the MySQL server?