Yesterday I was discussing with a friend of mine about how polymorphism is implemented in C++, and that is, using a virtual table ( remember the “virtual” keyword in method definitions? ). A virtual table is, rawly speaking, just like an array of function pointers. Each created object with virtual methods needs a virtual table. So, where does the virtual table is stored?, I really don’t know, but I do know where I can find the address of the virtual table associated to an object ( at least in g++ 4.1.1 ), the first sizeof(void*) bytes of an object are used to store a pointer to the virtual table. With this knowledge, one could think that is possible to override the virtual table pointer of the object and call arbitrary functions, and yes, we can. Let’s see some fun code.
Linux进程、内核及文件系统总结
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Linux
fork
一般我们会调用exec执行另一个程序，此时会用全新的程序替换子进程的正文，数据，堆和栈等。此时保存文件描述符的变量当然也不存在 了，我们就无法关闭无用的文件描述符了。所以通常我们会fork子进程后在子进程中直接执行close关掉无用的文件描述符，然后再执行exec。
但是在复杂系统中，有时我们fork子进程时已经不知道打开了多少个文件描述符（包括socket句柄等），这此时进行逐一清理确实有很大难 度。我们期望的是能在fork子进程前打开某个文件句柄时就指定好：“这个句柄我在fork子进程后执行exec时就关闭”。其实时有这样的方法的：即所 谓 的 close-on-exec。
回到我们的应用场景中来，只要我们在创建socket的时候加上 SOCK_CLOEXEC标志，就能够达到我们要求的效果，在fork子进程中执行exec的时候，会清理掉父进程创建的socket。
(Google Developer) Protocol Buffers Encoding
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Protobuf
This document describes the binary wire format for protocol buffer messages. You don’t need to understand this to use protocol buffers in your applications, but it can be very useful to know how different protocol buffer formats affect the size of your encoded messages.
C++异常机制的实现方式和开销分析（转载）
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编程语言
在我几年前开始写《C++编码规范与指导》一文时，就已经规划着要加入这样一篇讨论 C++ 异常机制的文章了。没想到时隔几年以后才有机会把这个尾巴补完 :-)。
还是那句开场白：“在恰当的场合使用恰当的特性” 对每个称职的 C++ 程序员来说都是一个基本标准。想要做到这点，就必须要了解语言中每个特性的实现方式及其时空开销。异常处理由于涉及大量底层内容，向来是 C++ 各种高级机制中较难理解和透彻掌握的部分。本文将在尽量少引入底层细节的前提下，讨论 C++ 中这一崭新特性，并分析其实现开销：
理解 Memory barrier（内存屏障）（转载）
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操作系统
本文例子均在 Linux（g++）下验证通过，CPU 为 X86-64 处理器架构。所有罗列的 Linux 内核代码也均在（或只在）X86-64 下有效。
本文首先通过范例（以及内核代码）来解释 Memory barrier，然后介绍一个利用 Memory barrier 实现的无锁环形缓冲区。
(MSDN) Heap Functions
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Windows
Each process has a default heap provided by the system. Applications that make frequent allocations from the heap can improve performance by using private heaps.
A private heap is a block of one or more pages in the address space of the calling process. After creating the private heap, the process uses functions such as HeapAlloc and HeapFree to manage the memory in that heap.
(MSDN) Comparing Memory Allocation Methods
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Windows
The following is a brief comparison of the various memory allocation methods:
- CoTaskMemAlloc
- GlobalAlloc
- HeapAlloc
- LocalAlloc
- malloc
- new
- VirtualAlloc
Although the GlobalAlloc, LocalAlloc, and HeapAlloc functions ultimately allocate memory from the same heap, each provides a slightly different set of functionality. For example, HeapAlloc can be instructed to raise an exception if memory could not be allocated, a capability not available with LocalAlloc. LocalAlloc supports allocation of handles which permit the underlying memory to be moved by a reallocation without changing the handle value, a capability not available with HeapAlloc.
Allocating and freeing memory across module boundaries（转载）
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Windows
I’m sure it’s been drilled into your head by now that you have to free memory with the same allocator that allocated it. LocalAlloc matches LocalFree, GlobalAlloc matches GlobalFree, new[] matches delete[]. But this rule goes deeper.
关于DLL的一些你不会想要知道的知识
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Windows
英文版本 Everything You Never Wanted To Know About DLLs.
最近因为一些原因，我需要调研动态链接在Windows平台上的实现细节。这篇文章主要是总结我在这个问题上所学到的知识，用于我将来的回顾和参考，但同时我也希望这篇文章对其他人所有帮助，因为我将要总结的这些内容，你可能需要东找西找才能找到。
废话不多说，让我们开始这趟旅程吧：
IOCP的使用和技术内幕
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Windows