New vs. Malloc，当重载New时

本文介绍了New vs. Malloc，当重载New时的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我重载新和删除以实现我自己的小对象/线程安全分配器。 / p>

问题是，当我重载 new 时，我不能使用 new 不破坏通用因果关系或至少编译器。大多数例子中，我发现 new 是重载的，使用 Malloc（）做实际分配。但是从我对C ++的理解来看， Malloc（）根本没有用例。

与此类似的答案，一些在SO之外的侵权行为较少：我在什么情况下使用malloc vs new？

我的问题是，当重载operator new时，如何分配实际内存 c>

（这不是好奇心） ，

解决方案

Short答案：如果您不想要现有的 malloc ，您需要实现自己的堆管理器。

一个堆管理器，例如Linux中的glibc中的 malloc ，Windows中的 HeapAlloc 级别算法。首先，请记住，堆被优化用于分配小尺寸的对象，如4〜512字节。

如何实现自己的堆管理器？至少，您必须调用在您的进程中分配内存块的系统API。对于Windows，有 VirtualAlloc ，对于Linux有 sbrk 。这些API分配大量内存，但大小必须是 page 大小的倍数。通常，x86和Windows / Linux中的页面大小为4KB。

获取一大块页面后，您需要实现自己的算法，内存转换为更小的请求。一个经典的（仍然很实用的）实现和算法是 dlmalloc ： g.oswego.edu/dl/html/malloc.html

要实现，您需要有多个数据保存结构和一些优化策略。例如，对于像16,20,36，256字节这样的小对象，堆管理器维护每个大小的块的列表。所以，有一个列表的列表。如果请求的大小大于页面大小，则只需调用 VirtualAlloc 或 sbrk 。然而，高效的实施是非常具有挑战性的。您不仅必须考虑速度和空间开销，还必须考虑缓存位置和碎片。

如果您对为多线程环境优化的堆管理器感兴趣，请查看 tcmalloc ： http：// goog-perftools。 sourceforge/doc/tcmalloc.html

I'm overloading new and delete to implement my own small-objects/thread-safe allocator.

The problem is that when I am overloading new, I cannot use new without breaking universal causality or at least the compiler. Most examples I found where new is overloaded, use Malloc() to do the actual allocation. But from what I understood of C++, there is no use-case for Malloc() at all.

Multiple answers similar to this one, some with less tort outside of SO: In what cases do I use malloc vs new?

My question, is how do I allocate the actual memory when overloading operator new without using Malloc() ?

(This is out of curiosity more than anything, try not to take the reasoning behind the overload too seriously; I have a seperate question out on that anywho!)

解决方案

Short answer: if you don't want existing malloc, you need to implement your own heap manager.

A heap manager, for example malloc in glibc of Linux, HeapAlloc in Windows, is a user-level algorithm. First, keep in mind that heap is optimized for allocating small sizes of objects like 4~512 bytes.

How to implement your own heap manager? At least, you must call a system API that allocates a memory chunk in your process. There are VirtualAlloc for Windows and sbrk for Linux. These APIs allocate a large chunk of memory, but the size must be multiple of page size. Typically, the size of page in x86 and Windows/Linux is 4KB.

After obtaining a chunk of page, you need to implement your own algorithms how to chop down this big memory into smaller requests. A classic (still very practical) implementation and algorithm is dlmalloc: g.oswego.edu/dl/html/malloc.html

To implement, you need to have several data structures for book-keeping and a number of policies for optimization. For example, for small objects like 16, 20, 36, 256 bytes, a heap manager maintains a list of blocks of each size. So, there are a list of lists. If requested size is bigger than a page size, then it just call VirtualAlloc or sbrk. However, an efficient implementation is very challenging. You must consider not only speed and space overhead, but also cache locality and fragmentation.

If you are interested in heap managers optimized for multithreaded environment, take a look a tcmalloc: goog-perftools.sourceforge/doc/tcmalloc.html