[fpc-devel] Mem-leak, where?

[Joost van der Sluis]

Op woensdag 26-09-2007 om 02:29 uur [tijdzone +0400], schreef Sergei
Gorelkin:
> Joost van der Sluis wrote:
> > ----
> > program testbug9751;
> > 
> > {$mode objfpc}{$H+}
> > 
> > uses
> >   Classes, SysUtils, mysql41dyn;
> > 
> > var hmysql : PMYSQL;
> > 
> > begin
> > //  InitialiseMysql; <-- remove the comment and the leakage is gone
> >   repeat
> >   InitialiseMysql;
> >   hmysql := nil;
> >   hmysql := mysql_init(hmysql);
> > // Comment the next line and the leakage is gone
> >   HMySQL:=mysql_real_connect(HMySQL,PChar(''),PChar(''),Pchar(''),Nil,0,Nil,0);
> >   mysql_close(hmysql);
> >   ReleaseMysql;
> >   until 1<0;
> > end.
> > ----
> 
> Looks like mysql_real_connect() overwrites hmysql variable? The value 
> returned by mysql_init() is not passed to mysql_close(), and the library 
> may not unload in this case.
> If you comment mysql_real_connect(), handle returned by mysql_init() IS 
> passed to mysql_close().

I also thought that. But that's not the case. From the
mysql-documentation:
(http://dev.mysql.com/doc/refman/5.0/en/mysql-real-connect.html)

----
Return Values 

A MYSQL* connection handle if the connection was successful, NULL if the
connection was unsuccessful. For a successful connection, the return
value is the same as the value of the first parameter. 
----

Also in the case of a succesfull connection, this code leaks...

I've rewritten the code, so that it's more clear what happens:
-----
program testbug9751;

{$mode objfpc}{$H+}

uses
  Classes, SysUtils, mysql41dyn,dynlibs;

var hmysql : PMYSQL;
    LH : TLibHandle;

begin
  repeat // repeat here gives troubles
  LH := loadlibrary(mysqllib);
  pointer(mysql_init) := GetProcedureAddress(LH,'mysql_init');
  pointer(mysql_real_connect) := GetProcedureAddress(LH,'mysql_real_connect');
  pointer(mysql_close) := GetProcedureAddress(LH,'mysql_close');

// repeat; <- if the repeat is placed here, the problems are gone
  hmysql := nil;
  hmysql := mysql_init(hmysql);
// Remove the next line and the problem is gone.
  HMySQL:=mysql_real_connect(HMySQL,PChar('192.168.3.1'),PChar('root'),Pchar('rosivrepus'),Nil,0,Nil,0);
  mysql_close(hmysql);

//  until 1<0; <- if the until is placed here, the problems are gone
  UnloadLibrary(LH);
  until 1<0; // until here gives troubles
end.
-----

so you can solve the leak by two ways:
1: remove the mysql_real_connect
2: move the repeat-until so that the 'initialisation' is outside the
loop

Joost.