[fpc-devel] Bug in PWidechar and refcounting
Hi all, the bug-report on the website doesn't work, so I write a mail: If you assign a widechar to a pwidechar, the refcount isn't increased. This construct is often used in the variants-code, which is allowed, according to the comments at the top of wstrings.inc. An example: Program test; var PW: PWideChar; dummy : AnsiString; procedure Set_PW; var W : WideString; s : ansistring; begin s := 'Hello world'; // Can't assign directly to W, because that's W := s; // interpreted as a constant with a refcount of -1 PW := PWideChar(W); // <- Bug, refcount of W (and PW) isn't increased end; // <- Memory at @W is deallocated, since refcount=0 begin Set_PW; SetLength(Dummy,3); // The dummy is allocated at the same address as PW writeln(pchar(PW)[0]); // Should write 'H', but it doesn't end. JoJo, Joost. ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
RE: [fpc-devel] Bug in PWidechar and refcounting
this is not a bug if when someone does pcharvar := ansistringvar or pwidecharvar := widestringvar we increased the refcount every program that used that construct would leak memory. where compiler automated types like ansistring and widestring meet non automated types like pchar and pwidechar some care is required on the part of the developer. If you don't like this move to a nanny state language like java. > -Original Message- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Joost van > der Sluis > Sent: 13 February 2005 00:32 > To: FPC developers' list > Subject: [fpc-devel] Bug in PWidechar and refcounting > > > Hi all, > > the bug-report on the website doesn't work, so I write a mail: > > If you assign a widechar to a pwidechar, the refcount isn't > increased. This construct is often used in the variants-code, which is > allowed, according to the comments at the top of wstrings.inc. > > An example: > > Program test; > > var PW: PWideChar; > dummy : AnsiString; > > procedure Set_PW; > > var > W : WideString; > s : ansistring; > > begin > s := 'Hello world'; // Can't assign directly to W, because that's > W := s; // interpreted as a constant with a refcount of -1 > > PW := PWideChar(W); // <- Bug, refcount of W (and PW) isn't increased > end; // <- Memory at @W is deallocated, since refcount=0 > > begin > Set_PW; > SetLength(Dummy,3); // The dummy is allocated at the same > address as PW > writeln(pchar(PW)[0]); // Should write 'H', but it doesn't > end. > > > JoJo, > Joost. > > > > ___ > fpc-devel maillist - fpc-devel@lists.freepascal.org > http://lists.freepascal.org/mailman/listinfo/fpc-devel ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
RE: [fpc-devel] Bug in PWidechar and refcounting
> if when someone does pcharvar := ansistringvar or pwidecharvar := > widestringvar we increased the refcount every program that used that > construct would leak memory. Normally I would aggree with you, but as far as I can see, PWideChar is also an automated type. (If not then large parts of the variant-code in the RTL has to be rewritten, and probably alsoe the wstrings.inc file) >From wstrings.inc: WideString is defined as a 'silent' pwidechar : a pwidechar that points to : @-8 : SizeInt for reference count; @-4 : SizeInt for size; @: String + Terminating #0; Pwidechar(Widestring) is a valid typecast. So WS[i] is converted to the address @WS+i-1. So there is a bug somewhere. But if they should not be refcounted, that's ok. But then I have some fixs for the variant-code Joost ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Bug in PWidechar and refcounting
Normally I would aggree with you, but as far as I can see, PWideChar is also an automated type. (If not then large parts of the variant-code in the RTL has to be rewritten, and probably alsoe the wstrings.inc file) From wstrings.inc: WideString is defined as a 'silent' pwidechar : a pwidechar that points to : @-8 : SizeInt for reference count; @-4 : SizeInt for size; @: String + Terminating #0; Pwidechar(Widestring) is a valid typecast. So WS[i] is converted to the address @WS+i-1. So there is a bug somewhere. But if they should not be refcounted, that's ok. But then I have some fixs for the variant-code Above is just an internal description of WideString layout in memory, so this layout allows easy type conversion of WideString to PWideChar. Note: PWideChar, PAnsiChar, PChar are just pointers and not garbage collected by compiler. But AnsiString and WideString are compiler managed types. So, as Peter mentioned, behaviour you are seeing is by design. ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Bug in PWidechar and refcounting
> Hi all, > > the bug-report on the website doesn't work, so I write a mail: > > If you assign a widechar to a pwidechar, the refcount isn't > increased. This construct is often used in the variants-code, which is > allowed, according to the comments at the top of wstrings.inc. > > An example: > > Program test; > > var PW: PWideChar; > dummy : AnsiString; > > procedure Set_PW; > > var > W : WideString; > s : ansistring; > > begin > s := 'Hello world'; // Can't assign directly to W, because that's > W := s; // interpreted as a constant with a refcount of -1 > > PW := PWideChar(W); // <- Bug, refcount of W (and PW) isn't increased > end; // <- Memory at @W is deallocated, since refcount=0 Kylix doesn't increase the refcount. Add the following line before and after the assignment to print the refcount: writeln(plongint(pchar(w)-8)^); ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Bug in PWidechar and refcounting
> Hi all, > > the bug-report on the website doesn't work, so I write a mail: > > If you assign a widechar to a pwidechar, the refcount isn't > increased. This construct is often used in the variants-code, which is > allowed, according to the comments at the top of wstrings.inc. > > An example: > > Program test; > > var PW: PWideChar; > dummy : AnsiString; > > procedure Set_PW; > > var > W : WideString; > s : ansistring; > > begin > s := 'Hello world'; // Can't assign directly to W, because that's > W := s; // interpreted as a constant with a refcount of -1 > > PW := PWideChar(W); // <- Bug, refcount of W (and PW) isn't increased > end; // <- Memory at @W is deallocated, since refcount=0 Kylix doesn't increase the refcount. Add the following line before and after the assignment to print the refcount: writeln(plongint(pchar(w)-8)^); ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Bug in PWidechar and refcounting
> Hi all, > > the bug-report on the website doesn't work, so I write a mail: > > If you assign a widechar to a pwidechar, the refcount isn't > increased. This construct is often used in the variants-code, which is > allowed, according to the comments at the top of wstrings.inc. > > An example: > > Program test; > > var PW: PWideChar; > dummy : AnsiString; > > procedure Set_PW; > > var > W : WideString; > s : ansistring; > > begin > s := 'Hello world'; // Can't assign directly to W, because that's > W := s; // interpreted as a constant with a refcount of -1 > > PW := PWideChar(W); // <- Bug, refcount of W (and PW) isn't increased > end; // <- Memory at @W is deallocated, since refcount=0 Kylix doesn't increase the refcount. Add the following line before and after the assignment to print the refcount: writeln(plongint(pchar(w)-8)^); ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Bug in PWidechar and refcounting
Alexey Barkovoy wrote: > PAnsiChar, PChar are just pointers and not garbage collected by compiler. But > AnsiString and WideString are compiler managed types. So, as Peter mentioned, > behaviour you are seeing is by design. In Delphi WideString is not reference counted at all. The layout of the string prefix is dictated by the Windows API (BSTR type), and AFAIK Windows also doesn't use reference counting with this type, or with OLEVariants containing wide strings. DoDi ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Bug in PWidechar and refcounting
> Alexey Barkovoy wrote: >> PAnsiChar, PChar are just pointers and not garbage collected by >> compiler. But >> AnsiString and WideString are compiler managed types. So, as Peter >> mentioned, >> behaviour you are seeing is by design. > > In Delphi WideString is not reference counted at all. The layout of the > string prefix is dictated by the Windows API (BSTR type), and AFAIK > Windows also doesn't use reference counting with this type, or with > OLEVariants containing wide strings. That is something Windows specific. For Kylix it is reference counted. ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
Re: [fpc-devel] Bug in PWidechar and refcounting
- Original Message - From: "DrDiettrich" <[EMAIL PROTECTED]> To: "FPC developers' list" Sent: Tuesday, February 15, 2005 4:11 AM Subject: Re: [fpc-devel] Bug in PWidechar and refcounting Alexey Barkovoy wrote: PAnsiChar, PChar are just pointers and not garbage collected by compiler. But AnsiString and WideString are compiler managed types. So, as Peter mentioned, behaviour you are seeing is by design. In Delphi WideString is not reference counted at all. The layout of the string prefix is dictated by the Windows API (BSTR type), and AFAIK Windows also doesn't use reference counting with this type, or with OLEVariants containing wide strings. In e-mail above I've not said anywhere about reference-counting, I've said WideString are managed by compiler. For example if you declare WideString local variable in procedure it will be automatically freed at the end of procedure in compiler generated "try ... finally" block. And if you declare PWideChar, allocate memory for it, when it's up to you to free this memory after you no longer need it. ___ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
