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</o:shapelayout></xml><![endif]--></head><body lang=EN-AU link=blue vlink=purple><div class=WordSection1><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif'> fpc-devel <fpc-devel-bounces@lists.freepascal.org> <b>On Behalf Of </b>Marcos Douglas B. Santos<br><b>Sent:</b> Monday, 30 July 2018 22:25<br><b>To:</b> FPC developers' list <fpc-devel@lists.freepascal.org><br><b>Subject:</b> Re: [fpc-devel] Why/how does the compiler have a non-trivial number ofmemory leaks after over two decades of development?<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><div><div><p class=MsoNormal>On Mon, Jul 30, 2018 at 9:14 AM, Sven Barth via fpc-devel <<a href="mailto:fpc-devel@lists.freepascal.org" target="_blank">fpc-devel@lists.freepascal.org</a>> wrote:<o:p></o:p></p><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><div><div><div><div><p class=MsoNormal>J. Gareth Moreton <<a href="mailto:gareth@moreton-family.com" target="_blank">gareth@moreton-family.com</a>> schrieb am Mo., 30. Juli 2018, 13:31:<o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><p class=MsoNormal>I've noticed that the compiler doesn't use <br>try...finally blocks to help with freeing <br>blocks. I'm not sure why this is the case, <br>but might be speed related.<o:p></o:p></p></blockquote></div></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Correct. Even implicit try-finally frame generation is disabled for the compiler source. <o:p></o:p></p></div></div></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Is performance more important than being correct? :|<o:p></o:p></p></div><div><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p></div></div></div></div></div><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Freeing memory is irrelevant if your process is going to exit anyway right after freeing it. The OS doesn’t care about any memory your process has allocated at that time. All pages go back into the available pool.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Depending on how the allocation/free behaviour of the compiler looks like, but it might even make sense to use a memory manager that doesn’t even know how to free memory.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>(I’m using windows terminology here, but I’m sure equivalent can be found on other platforms)<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Reserve a large block of address space.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Install a vectored exception handler that reacts to an access violation that falls inside the reserved block by committing the memory between start and error address + 1MB (or more or less).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Naïvely and without error checking, Alloc gets reduced to:<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>var<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> CurrentPtr: PByte;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>function Alloc(Size: Integer):Pointer;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>begin<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Size := (Size + 3) and not 3; //adjust depending on what allocation alignment is desired;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> If Size > 0 then begin<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Result := CurrentPtr;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> CurrentPtr := CurrentPtr + Size;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> end else<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Result := nil;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>end;<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>procedure Free(p: Pointer); <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>begin<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> {do nothing}<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>end;<o:p></o:p></span></p></div></body></html>