[fpc-pascal] Is System.IOResult thread-safe? (If not, I need to replace it.)

MegaBrutal megabrutal at gmail.com
Wed Nov 10 13:26:59 CET 2010


I'm new on the list. I have a problem. I've been trying to make my
application thread-safe by using lockfiles. I used System.Rewrite to
lock the file, and System.IOResult to check the result. But I've
encountered problems, and such problems are most likely occur, when
more than one thread's trying to lock the file at the same time. I've
been thinking what might be the problem, and I wondered if
System.IOResult is thread-safe or not. I suppose not. :( Not a big
deal, though, I may use an other function to lock the file in a
thread-safe manner.

This is my function (that tries to lock the file):

function TSpoolObjectReader.Open: boolean;
   {$I-} Rewrite(LockFile, 1); {$I+}
   if IOResult = 0 then begin
         MailFile:= TFileStream.Create('spool\' + Name + '.eml', fmOpenRead);
         SpoolData:= TINIFile.Create('spool\' + Name + '.dat');
         Envelope.ReturnPath:= SpoolData.ReadString('SpoolObject',
'Return-Path', '');
TIPNamePair.Create(SpoolData.ReadString('Originator', 'Name', ''),
            SpoolData.ReadString('Originator', 'IP', ''));
         FOpened:= true;
         Result:= true;
         Result:= false;
   else Result:= false;

The variable, "LockFile" is an untyped file, previously assigned. I
decided to use Rewrite instead of another TFileStream, because I guess
TFileStream acquires much more resources to implement features I don't
even use.

I'd like to ask your opinion, how should I replace Rewrite & IOResult. My ideas:
1. Use another TFileStream to acquire the lockfile. It should work,
however as I stated before, I guess it would acquire much unused
2. Use "FileOpen", I think such function exists in the Free Pascal
library, however I never used it, and I'm not sure is it thread-safe.
It should be, after all.
3. Use direct WinAPI call, CreateFile. In this case, my unit wouldn't
be cross-platform anymore. However, now I'm writing my program for
Windows, I'm considering porting it to Linux someday, thus I'd like to
avoid platform-specific calls wherever possible.

I think option 2 is the most preferable, but I'd like to hear your
opinions as well, or maybe you have a better idea.

Best regards,

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