FileOpen() and FileWrite() performance question

[Mechaflash]

As long as I want to write with ASCII chracters, is there a benefit to FileOpen() the file first before writing to it as opposed to just letting FileWrite() do all the work? Most instances, I would only write to a file a handful of times throughout a program for logging, reporting etc... which in my mind there wouldn't be any performance issues just using FileWrite(). But if I had a program which did huge amounts of logging and reporting, would it be recommended to FileOpen() it first... write to it throughout the program, then FileClose() it after all is said and done?

[Blue_Drache]

I don't really know much about the performance issues, but I just FileOpen(), do stuff, FileClose() if I need to do onesie-twosie stuff, and then FileOpen(), loop, FileClose() if I'm writing a bunch of stuff.

The benefits to using FileOpen() are helping to ensure that it's available when you need to write to it, instead of having to wait for another process to release the file, or risk unintentionally overwriting data or having your data unintentionally overwritten.

[Andreik]

FileWrite() will perform for you open/close operations. So should't be any any performance problem with just using FileWrite().

[JLogan3o13]

So, this interests me, as I have always used FileOpen first. I tested this out on an XP box with this code for FileOpen:

$var = FileOpen("C:Test.txt", 1)
For $i = 1 To 5000
  FileWrite($var, "This is a test of the Emergency Broadcast Network." & @CRLF)
Next

And this code for FileWrite:

For $i = 1 To 5000
  FileWrite("C:Test.txt", "This is a test of the Emergency Broadcast Network." & @CRLF)
Next

These are the times that I saw. I am using a virtualized instance of AutoIt, but don't believe that is a factor, as I get nearly the same times using a full install.

>Exit code: 0    Time: 1.851 - FileOpen   
                                                                         Creating File
>Exit code: 0    Time: 3.440 - FileWrite Only

>Exit code: 0    Time: 1.829 - FileOpen   
                                                                         File Exists
>Exit code: 0    Time: 3.433

[kylomas]

mechaflash213,

Try this and see what you think...

expandcollapse popup

;
;
;

#include <file.au3>
#include <date.au3>

Local $file1  = "c:tmpwrite_noopen_test", $block,$st, $incr = 200
Local $file2  = "c:tmpwrite_open_test", $block,$st

For $i = 0 To 2000
    $block &= chr(Random(32,127,1))
Next

$block &= @crlf

ConsoleWrite(' Block Used for filewrite test = ' & $block & @lf)
ConsoleWrite(' Start test w/o explicit open at ' & _now() & @lf)

For $i = 1 To 10
    $st = TimerInit()
    For $j = 1 To $i * $incr
        FileWrite($file1,$block)
    next
    ConsoleWrite('Iteration # ' & $i & ' = ' & Round(TimerDiff($st)/1000,4) & @lf)
next

ConsoleWrite(' Start test w   explicit open at ' & _now() & @lf)
Local $hfl = FileOpen($file2,1)

For $i = 1 To 10
    $st = TimerInit()
    For $j = 1 To $i * $incr
        FileWrite($hfl,$block)
    next
    ConsoleWrite('Iteration # ' & $i & ' = ' & Round(TimerDiff($st)/1000,4) & @lf)
next

kylomas

[BrewManNH]

If your file is very large, using FileOpen before FileWrite is a huge savings in time over just using FileWrite. Using parts of kylomas' script above I changed it so that it wrote 5000 lines of 2000 characters each, and this is what I get after running it the first time:

Start test w/o explicit open at 3/23/2012 2:04:11 PM

Iteration # 5001 = 24.8967

Start test w explicit open at 3/23/2012 2:04:36 PM

Iteration # 5001 = 0.0746

And this is what I get after running it twice where the file exists and is about 9.5MB in size after the first run.

Start test w/o explicit open at 3/23/2012 2:01:31 PM

Iteration # 5001 = 25.0751

Start test w explicit open at 3/23/2012 2:01:56 PM

Iteration # 5001 = 0.183

[Mechaflash]

are my eyes deceiving me... or am I reading it as if you don't call FileOpen() first, it takes 25 seconds... as opposed to 0.183 seconds??? (referencing your second run).

[BrewManNH]

Correct, it's writing 5000 lines of 2000 characters per line using FileWrite for each line. When you don't use FileOpen it is opening and closing the file everytime you use FileWrite, plus it has to start from the beginning of the file until it finds the end of the file so that it can append the new data to it every time, as the file gets bigger, the time gets longer because it's running through, eventually, 4999 lines of text just to add one more line. Whereas FileOpen/FileWrite keeps track of where the next line is supposed to go so it just puts it there right away.

[Mechaflash]

Okay that's understandable. Thanks for taking some time to perform a demonstration. I'm floating between like 3 projects at work now and didn't get a chance to plug in his code to run my own test.

[guinness]

I've personally use FileOpen, FileWrite & FileClose for the reasons mentioned above, it's the same for _FileWriteLog which I pass the handle to instead of the filename.