Re: [Lazarus] Safe temp file name
Thanks Graeme,Its like what I do so it seems Im doing OK. I looked at
the code and it seems it just remove { and }.
> if (LValue[1] = '{') and (LValue[cGUIDLength] = '}') then LValue
> := Copy(lValue, 2, cGUIDLength - 2); AAssignTo.AsString := LValue;
It seems it doesnt remove "-" .
> This may be an appropriate use for EnterCriticalSection and
> ExitCriticalSection, although why don't you just use a different
> "prefix" in the call to GetTempFile for each thread.
Yes I can but GUID is easier to use.
> I wasn't aware that GetTempFileName isn't threadsafe.
(Are you sure your code is correct?) Yea. If you look at the
implementation it just check until there isnt a file so if 2 thread get
a filename before they create it it cause a problem. In my case I made
100 thread and they will create temp file and use them,simple but some
time it will happen.
> var
GUID : TGUID; begin if CreateGUID(GUID) = 0 then begin MyFileName :=
GuiDToString(Guid); end;
Thanks.
Regards, Ara
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Re: [Lazarus] Safe temp file name
On 2015-11-25 15:27, Aradeonas wrote:
>> > if (LValue[1] = '{') and(LValue[cGUIDLength] = '}') thenLValue
>> > := Copy(lValue, 2, cGUIDLength - 2); AAssignTo.AsString := LValue;
> It seems it doesnt remove "-" .
>
Oops, my mistake. Yes, only { and } is removed in tiOPF code.
Regards,
- Graeme -
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Re: [Lazarus] Safe temp file name
On Wed, Nov 25, 2015 at 05:51:41AM -0800, Aradeonas wrote: > Hi, > > I used GetTempFileName in a multi thread system and it causes problems > as you guess already. So the best way in my mind is using GUID and maybe > use it in a loop for checking not existing for extra safety. But I want > to know is there any clean implementation already that I dont know of? It's pointless to check whether the file exists, since there's a race between checking whether the file exists and creating/using it. You need something that creates the file atomically only if it doesn't exist. For posix use open(2) with O_CREAT | O_EXCL. For Windows use CreateFile() with CREATE_NEW. When this fails, try again with another file name. Henry -- ___ Lazarus mailing list Lazarus@lists.lazarus.freepascal.org http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
Re: [Lazarus] Safe temp file name
Graeme Geldenhuys wrote:
Oops, my mistake. Yes, only { and } is removed in tiOPF code.
Why are the { and } actually removed?
As far as I know they can be part of a filename on all OSes (or am I wrong?)
Grtz,
Rik (rvk)
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Re: [Lazarus] Safe temp file name
On 2015-11-25 15:41, Rik van Kekem wrote:
> Why are the { and } actually removed?
>
> As far as I know they can be part of a filename on all OSes (or am I wrong?)
In tiOPF (the code I linked too), GUID's are used as an OID (Object ID),
and normally stored in a database field of type char(36). The { and }
was simply removed to save 2 bytes per record. I guess the "-" symbol
was left in place to make reading the OIDs (by a human) a bit easier -
most likely for debugging purposes only.
As for using the GUID value as a file name... I always followed the
example of tiOPF, but yes, modern file systems will allow the { and }
symbols in the file name without problem.
Regards,
- Graeme -
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Re: [Lazarus] Safe temp file name
Thank you Graeme. Can you point me to where this system implemented in tiOPF? Regards, Ara -- http://www.fastmail.com - The professional email service -- ___ Lazarus mailing list Lazarus@lists.lazarus.freepascal.org http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
Re: [Lazarus] Safe temp file name
This may be an appropriate use for EnterCriticalSection and ExitCriticalSection, although why don't you just use a different "prefix" in the call to GetTempFile for each thread. On 25/11/15 13:51, Aradeonas wrote: Hi, I used GetTempFileName in a multi thread system and it causes problems as you guess already. So the best way in my mind is using GUID and maybe use it in a loop for checking not existing for extra safety. But I want to know is there any clean implementation already that I dont know of? Regards, Ara -- http://www.fastmail.com - The way an email service should be -- ___ Lazarus mailing list Lazarus@lists.lazarus.freepascal.org http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus -- ___ Lazarus mailing list Lazarus@lists.lazarus.freepascal.org http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
Re: [Lazarus] Safe temp file name
Aradeonas wrote: > I used GetTempFileName in a multi thread system and it causes problems > as you guess already. I wasn't aware that GetTempFileName isn't threadsafe. (Are you sure your code is correct?) Graeme Geldenhuys wrote: On 2015-11-25 13:51, Aradeonas wrote: So the best way in my mind is using GUID and maybe use it in a loop for checking not existing for extra safety. So I think it is a pretty safe option to use as a temp file name, even in a multi-threaded environment. Even Microsoft advises it in case you use GetTempFileName excessively. > Due to the algorithm used to generate file names, *GetTempFileName* can perform poorly when creating a large number of files with the same prefix. In such cases, it is recommended that you construct unique file names based on *GUID*s. So it should be safe to use GUIDs for tempfilenames. FPC trunk has this: Guid := TGUID.NewGuid.toString; (I'm not sure if FPC 2.6.4 also some helpers for creating GUIDs) Grtz, Rik (rvk) -- ___ Lazarus mailing list Lazarus@lists.lazarus.freepascal.org http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
Re: [Lazarus] Safe temp file name
Rik van Kekem wrote:
(I'm not sure if FPC 2.6.4 also some helpers for creating GUIDs)
This will work in FPC 2.6.4:
var
GUID : TGUID;
begin
if CreateGUID(GUID) = 0 then
begin
MyFileName := GuiDToString(Guid);
end;
You could strip the {, } and - if you want.
Grtz,
Rik (rvk)
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[Lazarus] Safe temp file name
Hi, I used GetTempFileName in a multi thread system and it causes problems as you guess already. So the best way in my mind is using GUID and maybe use it in a loop for checking not existing for extra safety. But I want to know is there any clean implementation already that I dont know of? Regards, Ara -- http://www.fastmail.com - The way an email service should be -- ___ Lazarus mailing list Lazarus@lists.lazarus.freepascal.org http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
Re: [Lazarus] Safe temp file name
On 2015-11-25 13:51, Aradeonas wrote: > So the best way in my mind is using GUID and maybe > use it in a loop for checking not existing for extra safety. I've used GUID's as temp file names in a CGI application for about 5 years. The CGI app gets accessed all at the same time in a classroom environment by about 30-80 kids. I've never hit a duplicate GUID issue. I'm not saying it is impossible, I'm just saying the chances are very very slim. In tiOPF I also use GUID's as Object ID's. I've multiple times imported data which generates about 80,000-100,000 objects in memory in an instant. Again, used this software for many years, and never hit a single duplicate GUID. So I think it is a pretty safe option to use as a temp file name, even in a multi-threaded environment. Regards, - Graeme - -- fpGUI Toolkit - a cross-platform GUI toolkit using Free Pascal http://fpgui.sourceforge.net/ My public PGP key: http://tinyurl.com/graeme-pgp -- ___ Lazarus mailing list Lazarus@lists.lazarus.freepascal.org http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
