220 19151 <2328a5fd-924c-4d02-ac18-6a225f786dec@isocpp.org> article Path: news.gmane.org!not-for-mail From: Myriachan Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: New type of "new"/"delete" override Date: Tue, 21 Jul 2015 12:37:40 -0700 (PDT) Lines: 490 Approved: news@gmane.org Message-ID: <2328a5fd-924c-4d02-ac18-6a225f786dec@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1381_38275595.1437507460740" X-Trace: ger.gmane.org 1437507470 18236 80.91.229.3 (21 Jul 2015 19:37:50 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 21 Jul 2015 19:37:50 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDKLT4PURQHRBBV7XKWQKGQEJWELIOI@isocpp.org Tue Jul 21 21:37:44 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vn0-f71.google.com ([209.85.216.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZHdMF-00081g-OR for gclcip-std-proposals@m.gmane.org; Tue, 21 Jul 2015 21:37:44 +0200 Original-Received: by vnct143 with SMTP id t143sf146206816vnc.3 for ; Tue, 21 Jul 2015 12:37:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:subject:mime-version:content-type :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=v+nCy0KclP3/qj/LQct93zUQwW7WeOm58fdXbogPPa0=; b=PQPpb/uHqpD22z+0682Oh0rXrcCDuWWG0/Wa2l/6N9WrshlDmisB0DUgvkT9QEHS94 d/XZYzr5HenOC8c5t4OrHKIw/QNKpWje/TC1N8Q4etU/Fc1bKIFE8VFSZIYWNldV+ybu o4NMbLxMeEzzW8MpbQKRZqQC0/lql80rNOitWBoRu412t/g6CxFsXQ8w1ERdkXocZITb fTF7+AI62x46K5O214EiHJdvsppxhgeDo463iFj0Rqwz9F77Q1ryhowTb+muaVQO6uw4 kODhpkwA4aA1OzOsmmAEjG2OtsseRn5gbPuXdAIamjETZZ1K8TSqf9HHodKW5z748dyi i6OA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=v+nCy0KclP3/qj/LQct93zUQwW7WeOm58fdXbogPPa0=; b=c9z5Sm2joyoN1PSCbIzVuzCPhsrGHLkgnJOGvHdf72iHCMFBwKNYHdSv+BAXFX5/P9 xoT8z1K2xhznrhcmYHU5viZiPD51KEzZHvwzzCDfvelUJl8rIAHMGZ1q1dsFfXe5/qu2 G5m1sjbIXAVjRg0FspCHoCGQ/sVO+wayDBAuepQID3VY9nS3mXkl2xfr4wmtfYdWcXg4 uYU89VmcLTFICmKhvxV70zRyKdCiuOlUJdv5BZmEeqF+dN2A7gcDKTIASgmvivtl1ICi 01Nj2X+FRX19TlJ6WD7OC7M85HsaEScTzxO9fKeyTPkBnsn4Zb8u5Q7suMOMts78xDb2 j6pw== X-Gm-Message-State: ALoCoQmLxoPdsCaT3/VUbVSbumwnrZNV1kj9jEURFFgepyzugwvxbhjoudEZ+FtOce1qDEazGKZq X-Received: by 10.129.79.1 with SMTP id d1mr26797876ywb.45.1437507462794; Tue, 21 Jul 2015 12:37:42 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.43.167 with SMTP id x7ls19845igl.20.gmail; Tue, 21 Jul 2015 12:37:41 -0700 (PDT) X-Received: by 10.50.114.38 with SMTP id jd6mr344457igb.11.1437507461849; Tue, 21 Jul 2015 12:37:41 -0700 (PDT) X-Original-Sender: myriachan@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:19151 Archived-At: ------=_Part_1381_38275595.1437507460740 Content-Type: multipart/alternative; boundary="----=_Part_1382_2021806374.1437507460742" ------=_Part_1382_2021806374.1437507460742 Content-Type: text/plain; charset=UTF-8 In trying to implement a custom memory allocator, there are many annoyances that come up that make C++ difficult to work with. Particularly, the syntax of the new and delete operators means that using a custom memory allocator often involves macros that are semantically different from new and delete. When private and protected constructors and destructors get involved, things get especially annoying, because the allocator code can't call the constructor or destructor itself. I thought of an idea that would help with this issue, though it is admittedly rather crazy. I would add a new type of operator new overload: template Type *operator new valloc_new(const Constructor &constructor) noexcept(noexcept(constructor(static_cast(nullptr)))) { static_assert(alignof(Type) <= PAGE_SIZE, "only allocations of alignment PAGE_SIZE or less are supported") ; std::size_t headerSize = 0; // Custom implementations aren't required to use new_handlers void *memory = VirtualAlloc(nullptr, headerSize + sizeof(Type), MEM_COMMIT, PAGE_READWRITE); if (!memory) { throw std::bad_alloc("out of memory"); } try { return constructor(memory); } catch (...) { VirtualFree(memory, 0, MEM_RELEASE); throw; } } template void operator delete valloc_delete(Type *object, const Destructor & destructor) { if (object == nullptr) { return; } // Get the base address of the most-derived object void *memory = const_cast *>(object); if (std::is_polymorphic::value) { memory = dynamic_cast(const_cast *>( object)); } destructor(object); VirtualFree(memory, 0, MEM_RELEASE); } Now valloc_new and valloc_delete in the proper scope will syntactically function the same way as the new and delete keywords, in a way becoming keywords themselves. I think that it would be worthwhile to allow these to be scoped to namespaces or classes. The private constructor/destructor problem is solved, because they are passed in as lambdas (or function pointers, at implementation discretion). We can redefine the basic implementation of the "new" keyword to be an implementation-defined template function that calls ::operator new(size_t) and does other things, like dynamic_cast if the type is polymorphic. Overriding the global new would work by replacing this template or its overloads. template Type *operator new new(const Constructor &constructor, Args &&...args) noexcept( noexcept(constructor(static_cast(nullptr))) && noexcept(::operator new(std::size_t(), std::forward(args )...))); Melissa -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_1382_2021806374.1437507460742 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
In trying to implement a custom memory allocator, there ar= e many annoyances that come up that make C++ difficult to work with.=C2=A0 = Particularly, the syntax of the new and delete operators means that using a custom memory allocator often i= nvolves macros that are semantically different from new and delete.=C2=A0 When private and protected constr= uctors and destructors get involved, things get especially annoying, becaus= e the allocator code can't call the constructor or destructor itself.
I thought of an idea that would help with this issue, though it is ad= mittedly rather crazy.

I would add a new type of operator new overload:

= template <typename Type, typename Const= ructor>=
Type *operator new valloc_new(const Const= ructor &<= span style=3D"color: #000;" class=3D"styled-by-prettify">constructor= )
=C2=A0 =C2=A0 noexcept= (noexcept(constructor(static_cast<Type *>(nullptr))))
= {
=C2= =A0 =C2=A0 static_assert(align= of(= Type) <=3D PAGE_SIZE, "only allocations of alignment PAGE_SIZE or less are su= pported") ;

=C2=A0 =C2=A0 st= d::= size_t headerSize= =3D 0;

=C2=A0 =C2=A0 // Custom implementations aren&= #39;t required to use new_handlers
=C2=A0 =C2=A0 void *memory =3D <= /span>VirtualAllo= c(<= span style=3D"color: #008;" class=3D"styled-by-prettify">nullptr, headerSize + sizeof(Type), MEM_COMMIT, PAG= E_READWRITE);
=C2= =A0 =C2=A0 if (!memory)
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 throw std::bad_alloc("out of memory");
=C2=A0 =C2=A0 }

=C2=A0 =C2=A0 try
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 <= /span>return constructor(memory);
=C2=A0 =C2=A0 }
=C2=A0 =C2=A0 catch (...)
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 VirtualFree(memory, 0, MEM_RELEASE);
= =C2=A0 =C2=A0 =C2=A0 =C2=A0 throw;
=C2=A0 =C2=A0 }
}

template <typename Type, typename De= structor&g= t;
void operator delete valloc_delete(Type *object, const Destructor &destructor)
{
=C2=A0 =C2=A0 if = (object =3D=3D nullptr)
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 return;
=C2=A0 =C2=A0 }

=C2=A0 =C2=A0 // Get the base address o= f the most-derived object
=C2=A0 =C2=A0 void *= memory =3D= const_cast<std::remove_cv_t<Type> *>(object);
=C2= =A0 =C2=A0 if (std::is_polymorphic<Type>::value)
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 memory =3D dynamic_cast<void *>(const_cast<std::remove_cv_t<Type> *>(object));
=C2=A0 =C2=A0 }

=C2=A0 =C2=A0 destructor(object);

=C2=A0 =C2=A0 VirtualFree(memory, 0<= /span>, MEM_RELEASE<= span style=3D"color: #660;" class=3D"styled-by-prettify">);
}

<= br>
Now valloc_new and valloc_delete= in the proper scope will syntactically function the same way as the= new and delete keywords, in a w= ay becoming keywords themselves.=C2=A0 I think that it would be worthwhile = to allow these to be scoped to namespaces or classes.

The private co= nstructor/destructor problem is solved, because they are passed in as lambd= as (or function pointers, at implementation discretion).

We can rede= fine the basic implementation of the "new" keyword to be an imple= mentation-defined template function that calls ::operator new(size_t) and does other things= , like dynamic_cast<= void *> if the type is polymorphic.=C2=A0 Overriding the global n= ew would work by replacing this template or its overloads.

template <typename Type, typename= Construct= or,= typename... Args>
Type *<= /span>operator new new(const Constructor &con= structor,<= /span> Args &&...args)
=C2=A0 =C2=A0 noexcept(
=C2=A0 =C2=A0 =C2=A0 =C2=A0 noexcept= (constructor<= span style=3D"color: #660;" class=3D"styled-by-prettify">(static_cast<Type *>(nullptr))) &&
=C2=A0 =C2=A0 =C2=A0 =C2=A0 noexcept(::operator new(std::size_t<= span style=3D"color: #660;" class=3D"styled-by-prettify">(), std::forward<Args>(args)...)));


Melissa

--

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