高效的两段式循环缓冲区──BipBuffer

Simon Cooke，美国 （原作者）
北京理工大学 20981 陈罡(翻译)

写在前面的话：

    循环缓冲区是一个非常常用的数据存储结构，已经被广泛地用于连续、流数据的存储和通信应用中。对于循环缓冲区，传统的操作方法是开辟一块连续的存储区，不 断地写入数据，当写入到存储区的末尾的时候，再从存储区的首部再开始写入数据，由此不断地重复下去构成了循环缓冲区。偶曾经写过很多循环缓冲区，也看过很 多人编写的循环缓冲区，但是拜读Simon Cooke先生的文章────“两段式”循环缓冲区（原文名称是：The Bip Buffer - The Circular Buffer with a Twist）确实觉得与众不同，于是就有了把它介绍给国内开发者的意愿。这里的twist的意思是“缠绕、绞合”，在这里有紧密联系的意味，作者的本意是 希望通过twist这个词能够体现出这个循环缓冲区的特点，但是如果直译出来，会让很多人感到费解。所以在此，根据偶个人的理解将这个标题翻译成“两段 式”循环缓冲区。接下来偶会把英文原文跟偶的理解写出来，感兴趣的朋友可以对照着看，如果翻译有误的地方还请个位高手不吝斧正！

                                                                      ────译者

1、Introduction 简介

Instead of keeping one head and tail pointer to the data in the buffer, it maintains two revolving regions, allowing for fast data access without having to worry about wrapping at the end of the buffer.

Buffer allocations are always maintained as contiguous blocks, allowing the buffer to be used in a highly efficient manner with API calls, and also reducing the amount of copying which needs to be performed to put data into the buffer. Finally, a two-phase allocation system allows the user to pessimistically reserve an area of buffer space, and then trim back the buffer to commit to only the space which was used..

Let's cover a little history first. If you don't already know why a circular buffer can be implemented really efficiently in hardware, or why that makes them the buffer of choice in most electronics, here's why.

Bip-Buffer使用起来有些类似循环缓冲区，但是在结构上略有不同。Bip-Buffer内部采用了两个循环存储区（而不是靠维持头指针和尾指针） 来实现数据的高速存取，而且可以让Bip-Buffer的使用者完全不必担心写入数据到达缓冲区末尾，导致重新从缓冲区的首部开始写入的问题。Bip- Buffer维护的存储区是连续的，因此，Bip-Buffer可以通过API调用非常高效地使用存储区，在整个使用过程中可以最大限度避免使用诸如 memcpy(),memmove()之类的内存拷贝操作（通常对于循环缓冲区来说，频繁地调用内存操作函数会成为效率瓶颈）。最后，Bip- Buffer两段式的内存分配系统允许用户申请一块较大的内存，而通过Commit操作来确认真正需要的内存大小，然后把没有用完的内存回收。

在这之前，我们先来回顾一下历史。如果你不知道为什么循环缓冲区可以利用硬件来做得非常非常高效或者不明白为什么在许许多多的电子产品中都能找到循环缓冲区的影子，那么下面的描述将给你解答。

2.Back in Days of Old... “石器”时代

Once upon a time, computers were much simpler. They didn't have 64 bit data buses. Heck, they didn't even have real 16 bit registers - although you could occasionally convince a pair of them to sub in for that purpose. These were simpler times, where Real Men programmed in assembly language, and laughed at anyone who didn't know how to use the carry flag for all kinds of nefarious purposes.

在很久以前，计算机要简单得多，它们并没有64位的总线，甚至没有真正的16位的寄存器，尽管你可能会相信真的有一对寄存器在做减法计算（译者：这 句话很绕口,应该是作者在以一种调侃的语气跟读者交流，也不知道偶理解得对不对。作者的意思是暗指计算机是没有减法的，所谓减法就是在进行补码的加法运 算，但是对于编程人员来说，由于汇编指令集里面是有SUB指令的，或许有些初级的开发者根据这个指令会想当然地认为寄存器之间在做减法运算。）。在这个 “石器”时代，大师们使用汇编语言编写程序（译者，石刀、石斧？），他们会嘲笑那些不知道如何使用进位标志位来进行编程的开发者。

With simpler times came elegant hacks to eke the most power out of every instruction cycle available. Take, for example, a simple terminal communications program. Newer RS232 serial controllers had things like automatic handling of RTS and CTS signal lines to control the flow of data - but this came at a cost. Namely, the connection would be stopping and starting all the time, instead of streaming along. So in between the controller card and the system, would often be found a FIFO. This simple circular buffer was often no more than a couple of bytes long, but it meant that the system could run smoothly along without polling to see if data had arrived, or being hammered by constant interrupts from the serial controller.

在那个时代里，一流的黑客们想方设法地“压榨”计算机在每一条指令周期的运算能力。举个例子来说，一个简单的终端通信程序（译者，这里的终端通信， 指的是基于rs232的串行通信，在作者所指的那个时代，应该还没有所谓互联网这样的东西存在），较新的rs232串行控制器可以通过自动处理RTS和 CTS信号线来控制数据流向（但是这带来了一定程度的带宽资源浪费）。正如RTS和CTS这样的名字所代表的意思一样，串行通信的数据连接需要不断地处理 控制器开始和停止信号，而不是采用类似“流”的方式连续不断地传输数据。于是，在控制卡和系统之间，我们通常可以找到一个叫做FIFO（译者，可以理解为 数据结构中的先进先出型的队列）东西。这个或许是最简单的循环缓冲区的雏形，它通常只有几个到几十个字节左右的长度，但是它的出现，意味着整个系统可以流 畅地运行，不需要实时地检查（译者，也就是所谓的轮循）是否有新的数据到达，或者应用程序的执行过程不断地被串行控制器的硬件中断（译者，这里的中断应该 跟微机原理中学到的中断类似）所打扰。

Most FIFOs started out on-chip, but people also added their own in their code - the idea being that if you had some really gnarly dancing that you had to do on the incoming data, you may as well batch it all up into one lump and do it infrequently... giving spare time to the system to do other things. Like scroll the console, or decode GIFs.

绝大多数的FIFO都是在芯片上完成的，但是开发者们也会把这种理念用于他们的代码中，尤其是当某些通信连续性很糟糕的场合，需要开发者多次接收数 据，然后一次性读取出来处理的时候，很多人想到了循环缓冲区。有了它的帮助，开发者可以在等待的这段时间里让计算机做一些其它事情，例如滚动控制台输出或 者解码GIF图片之类的。

As I said, a FIFO is a very simple circular buffer. Most are implemented very simply as well; they're typically 2ⁿ bytes in size, which allows the pointers to simply overflow to get back around to the other end of the buffer. The FIFO logic can tell if the FIFO is empty because the head and tail values are the same, and it's full if the head is one greater than the tail.

正如我所提到的，FIFO是非常简单的循环缓冲区，而且绝大部分都是非常简单的实现；它们的长度一般都是2的n次方，这样就可以允许对指针进行简单 的溢出判断和处理完成指针重新指向缓冲区的起始位置。FIFO的逻辑可以很容易地通过头指针和尾指针的值来判断缓冲区是“空”还是“满”——头指针和尾指 针的数值相等，代表缓冲区为空；头指针的数值如果比尾指针大1，则代表缓冲区满。

Implementing these in software was easy on the old 8 bit systems. Take a 16 bit register pair. Decide on a location in memory (a multiple of 256) to store the FIFO data in. Then, after setting the register to the start of the buffer, don't touch the high register - just increment the low register. This gives you a 256-byte long buffer which you can walk through in one (in the case of the Zilog Z80, 4 cycles - the smallest execution unit available on that system) instruction. You can never go out of the bounds of your buffer, because the low register acts as an index with a value from 0 to 255. When you hit what would have been index 256, the register overflows and clocks back over to zero.

在老式的8位系统里面实现上述FIFO是非常简单的事情。找两个8位的寄存器构成一个16位的寄存器对，分配一段内存（取256的倍数）来保存 FIFO数据，然后，让寄存器对指向该段内存的起始地址（译者，8位的系统，一般寻址空间是16位的，作者的意思是要用两个8位的寄存器来保存16位的内 存地址，256的倍数代表了一个对齐问题，如果取256的倍数的话，就会让16位的寄存器对，只有高8位是有数值的，低8位是从0开始的），注意不要去碰 高8位的寄存器，就让它保留内存地址的值即可；然后可以使用8位模式来操作低8位寄存器对16位的寄存器对指向的内存地址进行FIFO数据写入操作，把低 8位的寄存器做为0－255的索引，每写入一个字节，就把低8位的寄存器加1，一旦超过了255，低8位的寄存器就会溢出，让低8位寄存器重新从0开始， 这样就由硬件自动完成了循环缓冲区指针的调整。用这种方式就为你提供了只需要一个指令周期就可以完成操作的256个字节的循环缓冲区（在Zilog Z80系统上面，需要4个指令周期，这是在该系统里可以得到的最小的执行单位）。在这个实现中，由于是采用硬件溢出的方式来调整循环缓冲区的指针，因此， 根本不必担心会溢出，会把数据写到其它的内存里面。（译者，这可能是可以用软件实现的效率最高、安全性最好的循环缓冲区了。）

3. The Modern Day “帝国”时代

Unfortunately, there is no solution quite as elegant available to Windows programmers today as that simple old 8-bit solution. Sure, you can dive down into assembly language (provided you can work out how the compiler maps registers to values... something I've never seen a good enough explanation of to get my head around), but most people don't have time for assembly language any more. And besides, we're dealing with 32 bit registers now - incrementing just one low-order byte from inside that register isn't really all that kosher any more. It can lead to cache flushing, pipeline stalling, printer fires, rains of frog, etc.
很不幸，对于现代windows程序开发人员来说，已经没有可能找到一种效率可以与早先8位机时代的FIFO相媲美的循环缓冲区的“完美”解决方案了。当 然了，你可以深入研究汇编语言（你可以知道编译器是如何把寄存器和程序中的数值映射起来，然后做某种优化。。。总之我从来没有看到过一个能够让我改变我的 这个看法的汇编解决方案），但是绝大多数人没有时间去挖掘汇编语言的潜力。而且，我们现代的操作系统都采用的是32位的寄存器，依靠寄存器加1，然后利用 硬件溢出来达到循环利用缓冲区的做法，基本上已经不太现实了。现代的操作系统会利用cache（缓存）技术，管道延迟技术，printer fires, rains of frog等等来扩大寻址的空间。（译者，这后面两个技术不知道是什么意思，还望知道的朋友提示一下。）

If you can't just clock the low-order register to walk through the buffer, you have to start worrying about things like checking to see how much buffer you have filled before the end, making sure that you remember to copy the rest of the data from the start of the buffer, and all kinds of other bookkeeping headaches.

如果不能够通过简单的自增低位寄存器来实现重复使用整个缓冲区的话，那么我们就不得不去面对诸如已经往缓冲区中写入了多少数据，如何确保当写到缓冲区末尾的时候，要把余下的数据从缓冲区的首部开始写入等等让人头疼的问题。

My first attempt at implementing something like this relied on the vague hope that the virtual memory system could be tricked into setting things up in such a way that you could set up a mirror of a section of memory right next to the original. The idea being that you could still use the rotating allocation of data; a copy operation could go at full speed without any checking to see if you'd walked off the end of the buffer - because as far as your process's address space is concerned, the end of your buffer is also the beginning of your buffer.
我的第一个在现代的操作系统中实现高效的FIFO循环缓冲区的设想是基于一个模糊的目标，希望能够欺骗虚拟内存系统，在当前缓冲区的后面做一个镜像的缓冲 区，这样一旦对这段缓冲区写入数据超过了内存的边界，数据会自动写入到当前当前缓冲区的起始位置去。这样，就可以仍然构成一个循环使用的存储区，而且内存 拷贝等的操作不需要检查当前指针是否到达了内存区的边界——这是因为进程的地址空间已经被修改过了，缓冲区末尾的再下一个字节的地址恰恰就是缓冲区的开始 的地址。（译者，作者的这个设想确实很有趣，但是估计现代的操作系统还没有开放到这个程度，估计用linux通过修改一些内核代码，应该是可以做到作者这 个想法的）

Now, this mirroring technique may actually work. Due to some restrictions, I decided not to implement it myself (yet - I'm sure I'll find a use for it some day). The idea behind it is that first one reserves two areas of virtual memory, side by side. One then maps the same temporary file into both virtual memory sections. Voila! Instant mirroring, and a nice large buffered expanse one can copy data from willy-nilly.
这个镜像技术的设想或许真的会工作，但是由于一些系统限制性的原因，我决定不去自己实现它（虽然现在没有，我肯定将来的什么时候我会为它找到一种应用方 式）。这个想法背后，意味着程序需要维护两块并列的虚拟内存，在两个虚拟内存中映射的是同一个临时文件。Instant mirroring技术(译者，这或许是作者一时激动，给这个设想起的名字吧。。。)最终可以允许用户无限制地向缓冲区写入数据、读取数据。

Unfortunately, while it should (again, I've not tried it) indeed work, there is another problem - namely, that files can only be mapped on 64kb boundaries (possibly larger on larger memory systems). This means that your buffer has to be a minimum of 64kb in size, and will take up 128kb of your virtual address space. Depending on your application, this may be a valid technique. However, I don't see writing a server application with 1000's of sockets being a valid prospect here.
So what to do? If mirroring won't work, how close can we get to using a circular buffer in our code? Heck, even if we can get close, why would we want to?
不幸的是，尽管它确实应该工作（再次声明，我没有尝试去做这个实验），但是会引起另外一个问题，也就是说文件只能被映射到64kb的边界（也许在更大的内 存系统中会大一些）。这就意味着缓冲区最小也需要64kb的大小，并且会用掉虚拟地址空间的128kb的寻址空间。无论如何，这取决于你的应用程序的规 模，这也许是一个可行的技术，但是我从没看到过为1000个socket端口提供服务的程序有采用这种技术的苗头。（译者，作者很无奈，毕竟想法是好的， 但是真实的服务器开发，需要的是可靠、稳定、以及高效，没人愿意为了测试那些还在设想中的技术而赌上自己的schedule :P）。

既然如此，该怎么办呢？如果这种mirroring的技术不能够工作，我们如何找到一种在效率上最最接近它的循环缓冲区的实现方案呢？假设我们可以做出这样的接近于上述方案的循环缓冲区，那么我们该如何做呢？

4 The Advantages of the Circular Buffer 使用循环缓冲区的优点
There are a number of key advantages to using a circular buffer for the temporary storage of data.When one puts data into a block of memory, one also has to take it out again to make use of it. (Or one can use it in place). It is useful to be able to make use of the data in the buffer while more data is being appended to the buffer. However, as one frees up space at the head of the buffer, that space is no longer usable, unless one copies all of the data in the buffer which has not yet been used to the beginning of the buffer. This frees up space at the end of the buffer, allowing more data to be appended.
使用循环缓冲区存储临时数据的优点不可胜数。当开发者把数据存入一块临时缓冲区以后，他一定会在什么时候为了使用这个数据而把数据读取出来（或者直接使用 临时缓冲区中的数据）。在缓冲区中直接操作和使用数据的同时，缓冲区需要支持继续向数据末尾追加数据，这个特性是非常有用的。但是在通常情况下，缓冲区前 面部分的数据一旦被释放，这部分缓冲区就不再可用，除非把缓冲区后部的所有没有用到的数据都向前移动到缓冲区的起始位置。

There are a couple of ways around this; one can simply copy the data (which is a reasonably expensive proposition), or one can extend the buffer to allow more data to be appended (a massively expensive process).With a circular buffer, the free space in the buffer is always available to have data appended into it; the data is copied, the pointer adjusted, and that's that. No copying, no reallocation, no worries. The buffer is allocated once, and then remains useful for its entire life.
围绕着临时缓冲区的使用方法，有很多种不同的做法；最简单的一种就是直接把数据拷贝出来使用（这当然是一种效率非常低下的做法），或者动态扩展缓冲区的长 度（这涉及到系统的内存分配和释放，是效率更加低下的做法）。而使用循环缓冲区，可以总是有可用的内存来写入数据；数据可以任意拷贝，可以直接通过指针来 对数据进行存取等等。缓冲区只需要分配一次即可在其整个生存周期中发挥作用，不需要从新分配，不需要拷贝数据（译者，这里的不需要拷贝数据是指，Bip- Buffer是支持直接用指针来写入数据的，因此不需要内存拷贝之类的操作。）

5 A Fly In The Ointment 循环缓冲区美中不足的地方
One could simply implement a circular buffer by allocating a chunk of memory, and maintaining pointers. When one walked off the end of the buffer, the pointer would be adjusted - and this operation would be reflected in every operation that is performed, whether copying data into the buffer or removing it. Length calculations are slightly more complicated than normal, but not overly so - simple inline functions take care of that problem with ease, sweeping it under the rug.
Unfortunately, most API calls don't believe in circular buffers. You have to pass them a single contiguous block of memory which they can access, and there is no way for you to modify their write behavior to adjust pointers when they cross the end of the buffer. So what to do? Well, this is where the Bip-Buffer comes in.

人们可以通过简单的分配一块内存，小心地维护指向其的指针来实现一个循环缓冲区。当数据写入到缓冲区的末尾的时候，应该将数据写入指针调整到缓 冲区起始，这个看似简单的操作影响到对缓冲区的所有操作，无论是把数据写入还是读出。缓冲区中已用数据的长度的计算要比往常复杂一点，效率会稍微低一点 （但是这一点可以通过inline函数很轻易地解决），可以不足为虑。

不幸的是，绝大多数的api调用是不支持循环缓冲区的，很多情况下，人们不得不为这些api传入连续的装满数据的内存区，在api函数使用这块内存区的时候是无法调整其读取或写入指针到循环缓冲区的开头的。那该如何是好？别着急，这就是Bip-Buffer存在的理由。

6 Enter The Bip-Buffer 进一步了解Bip-Buffer
If one cannot pass a circular buffer into an API function, then one needs an alternative that will work - preferably with many of the same advantages as the circular buffer. It is possible to build a circular buffer which is split into two regions - or which is bi-partite (and that's how you get the Bip in a Bip-Buffer). Each of the two regions move through the buffer, starting at the left and ending up at the right hand side. When one runs out of space for appending data, if there is only one region, a new one is created at the beginning (if possible). The diagram below shows how it works in more detail.

如果人们不能直接把循环缓冲区直接做为参数传入api函数，那么就需要另外一种解决方案——这种方案是一个既要拥有与循环缓冲区一样的优点，又 要没有上述缺点的方案。建立一个循环缓冲区，但是在缓冲区内部将分配的两次内存，内部维护个两个区域；或者简单地来说，将传统的为循环缓冲区分配的一块内 存分裂成两块内存缓冲区来使用，这里的分裂（bi-partite）也是Bip-Buffer前面的Bip这个缩写的由来。两块内存区都是从左往右来写入 数据的，在申请缓冲区的时候，当一个缓冲区满了，就会马上从另外一个内存区的起始地点开始写入，这样就避免了调整头指针的问题。下面的图例就明确地显示了 它是如何工作的：

The buffer starts out empty, with no regions present (figure 1). (eg. immediately after calling AllocatedBuffer)

整个缓冲区开始的时候是空的，没有分裂成两个区域（如图1所示，是调用AllocatedBuffer()函数以后的样子）

Then, when data is first put into the buffer, a single region (the 'A' region) is created (figure 2). (Say, by calling Reserve followed by Commit)

然后，当第一次将数据放到缓冲区以后（如图2所示，这是调用了Commit()函数以后的样子），创建了第一个区域（图中的'A'区域）

Data is added to the region, extending it to the right (figure 3).

当有数据继续写入的时候，都会被追加到区域A的数据的后面，使其向右不断伸展（如图3所示）

For the first time now, we remove data from the buffer (figure 4). (see the DecommitBlock call described below)

第一次从缓冲区中读出数据的样子（如图4所示，参见下面的关于DecommitBlock()函数的说明）

This continues until the region reaches the end of the buffer (figure 4). Once more free space is available to the left of region A than to the right of it, a second region (comically named "region B") is created in that space. The choice to create a new region when more space is available on the left is made to maximize the potential free space available for use in the buffer. The upshot of all this leaves us with something which looks rather like figure 5.

这种形式的写入和读出过程会持续下去，直到区域到达了缓冲区的末尾（如图4所示）。一旦在区域A左侧的可用空闲空间要大于区域A右侧的空闲空间，第二个区域（我们叫做区域B）就被创建出来，从此以后的内存分配就从这个区域B来分配（如图5所示）。

If we now use up more of the buffer space, we end up with figure 6, with new space only being allocated from the end of region B. If we eventually allocate enough data to use up all of the free space between regions A and B (figure 7), we no longer have any usable space in the buffer, and no more reservations can be performed until we read some data out of it.
如果继续使用缓冲区的空间，我们就会看到如图6所示的样子，区域B在不断扩展，将数据追加到区域B的后面。如果用光区域B与区域A之间的空间(如图7所示)，那么就真的没有内存可分配了，直到有一些数据从循环缓冲区中读出。

If we then read more data out of the buffer (say the entire remaining contents of region A), we exhaust it entirely. At the point, as region A is completely empty, we no longer need to track two separate regions, and all of region B's internal data is copied over region A's internal data, and region B is entirely cleared. (figure 8)
如果从缓冲区中读取更多的数据出来（假设整个区域A的数据都被读取出来），我们完全把区域A中存储的数据用光了，这时候区域A就完全空了，我们就不再需要 维护两个独立的区域了，这时，区域B就获得了整个缓冲区，可以继续追加数据，同时也支持从区域B中向外读取数据了（如图8所示）。

If we read a little more data out of the buffer, we now end up with something a lot like figure 4, and the cycle continues.
如果从缓冲区中读取更多的数据（如图9所示），我们最终又会得到类似图4所示的存储区使用状态，然后继续重复4,5,6,7,8这些状态的切换，完成循环利用缓冲区。

7 Characteristics of the Bip-Buffer BipBuffer的特点
The upshot of all of this is that on average, the buffer always has the maximal amount of free space available to be used, while not requiring any data copying or reallocation to free up space at the end of the buffer.
在绝大多数场合下，BipBuffer都可以充分利用全部缓冲区资源，而且即使到了缓冲区的末尾，也不需要任何数据拷贝或重新分配存储空间来实现循环利用缓冲区。

The biggest difference from an implementation standpoint between a regular circular buffer and the Bip Buffer is the fact that it only returns contiguous blocks. With a circular buffer, you need to worry about wrapping at the end of the buffer area - which is why for example if you look at Larry Antram's Fast Ring Buffer implementation, you'll see that you pass data into the buffer as a pointer and a length, the data from which is then copied byte by byte into the buffer to take into account the wrapping at the edges.

BipBuffer与常规的循环缓冲区相比较，最大的区别在于它可以返回连续的存储区。使用常规的循环缓冲区，需要考虑如何对缓冲区的末尾进行封 装。这也是当看到Larry Antram's Fast Ring Buffer文章中对于循环缓冲区实现的时候，会发现需要传入数据缓冲区的指针以及数据的长度，然后数据会一个字节一个字节地拷贝到循环缓冲区中去（当然 他的这种实现是需要考虑缓冲区的边界问题的。）

Another possibility which was brought up in the bulletin board (and the person who brought it up shall remain nameless, if just because they... erm...are nameless) was that of just splitting the calls across wraps. Well, this is one way of working around the wrapping problem, but it has the unfortunate side-effect that as your buffer fills, the amount of free space which you pass out to any calls always decreases to 1 byte at the minimum - even if you've got another 128kb of free space at the beginning of your buffer, at the end of it you're still going to have to deal with ever shrinking block sizes. The Bip-Buffer neatly sidesteps this issue by just leaving that space alone if the amount you request is larger than the remaining space at the end of the buffer. When writing networking code, this is very useful; you always want to try to receive as much data as possible, but you never can guarantee how much you're going to get. (For most optimal results, I'd recommend allocating a buffer which is some multiple of your MTU size).

Yes, you are going to lose some of what would have been free space at the end of the buffer. It's a small price to pay for playing nicely with the API.

Use of this buffer does require that one checks twice to see if the buffer has been emptied; as one has to deal with the possibility that there are two regions currently in use. However, the flexibility and performance gains outweigh this minor inconvenience.

class BipBuffer
{
private:
    BYTE* pBuffer;
    int ixa, sza, ixb, szb, buflen, ixResrv, szResrv;

public:
    BipBuffer();

The constructor initializes the internal variables for tracking regions, and memory pointers to null; it does not allocate any memory for the buffer, in case one needs to use the class in an environment where exception handling cannot be used.

~BipBuffer();

The destructor simply frees any memory which has been allocated to the buffer.

bool AllocateBuffer(int buffersize = 4096);

AllocateBuffer allocates a buffer from virtual memory. The size of the buffer is rounded up to the nearest full page size. The function returns true if successful, or false if the buffer cannot be allocated.

void FreeBuffer();

FreeBuffer frees any memory allocated to the buffer by the call to AllocateBuffer, and releases any regions allocated within the Bip-Buffer.

bool IsInitialized() const;

IsInitialized returns true if the buffer has had memory allocated to it (by calling AllocateBuffer), or false if there is no memory allocated to the buffer.

int GetBufferSize() const;

GetBufferSize returns the total size (in bytes) of the buffer. This may be greater than the value passed into AllocateBuffer, if that value was not a multiple of the system's page size.

void Clear();

Clear ... well... clears the buffer. It does not free any memory allocated to the buffer; it merely resets the region pointers back to null, making the full buffer usable for new data again.

BYTE* Reserve(int size, OUT int& reserved);

Now to the nitty-gritty. Allocating data in the Bip-Buffer is a two-phase operation. First an area is reserved by calling the Reserve function; then, that area is Committed by calling the Commit function. This allows one to, say, reserve memory for an IO call, and when that IO call fails, pretend it never happened. Or alternatively, in a call to an overlapped WSARecv() function, it allows one to advertise how much memory is available to the network stack to use for incoming data, and then adjust the amount of space used based on how much data was actually read in (which may be less than the requested amount).

To use Reserve, pass in the size of block requested. The function will return the size of the largest free block available which is less than or equal tosize in length in the reserved parameter you passed in. It will also return a BYTE* pointer to the area of the buffer which you have reserved.

In the case where the buffer has no space available, Reserve will return a NULL pointer, andreserved will be set to zero.

Note: you cannot nest calls to Reserve and Commit; after calling Reserve you must call Commit before calling Reserve again.

void Commit(int size);

Here's the other half of the allocation. Commit takes a size parameter, which is the number of bytes (starting at the BYTE* you were passed back from Reserve) which you have actually used and want to keep in the buffer. If you pass in zero for this size, the reservation will be completely released, as if you had never reserved any space at all. Alternatively, in a debug build, if one passes in a value greater than the original reservation, an assert will fire. (In a release build, the original reservation size will be used, and no one will be any the wiser). Committing data to the buffer makes it available for routines which take data back out of the buffer.

The diagram above shows how Reserve and Commit work. When you call Reserve, it will return a pointer to the beginning of the gray area above (fig. 1). Say you then only use as much of that buffer as the blue section (fig 2). It'd be a shame to leave this area allocated and going to waste, so you can call Commit with only as much data as you used, which gives you fig. 3 - namely, the committed space extends to fill just the part you needed, leaving the rest free.

int GetReservationSize() const;

If at any time you need to find out if you have a pending reservation, or need to find out that reservation's size, you can call GetReservationSize to find the amount reserved. No reservation? You'll get a zero back.

BYTE* GetContiguousBlock(OUT int& size);

Well, after all this work to put stuff into the buffer, we'd better have a way of getting it out again.

First of all, what if you need to work out how much data (total) is available to be read from the buffer?

int GetCommittedSize() const;

One method is to call GetCommittedSize, which will return the total length of data in the buffer - that's the total size of both regions combined. I would not recommend relying on this number, because it's very easy to forget that you have two regions in the Bip-Buffer if you do. And that would be a bad thing (as several weeks of painful debugging experience has proved to me). As an alternative, you can call:

BYTE* GetContiguousBlock(OUT int& size);

... which will return a BYTE* pointer to the first (as in FIFO, not left-most) contiguous region of committed data in the buffer. Thesize parameter is also updated with the length of the block. If no data is available, the function returns NULL (and thesize parameter is set to zero).

In order to fully empty the buffer, you may wish to loop around, calling GetContiguousBlock until it returns NULL. If you're feeling miserly, you can call it only twice. However, I'd recommend the former; it means you can forget that there's two regions, and just remember that there's more than one.

void DecommitBlock(int size);

So what do you do after you've consumed data from the buffer? Well, in keeping with the spirit of the aforementioned Reserve and Commit calls, you then call DecommitBlock to release data from it. Data is released in FIFO order, from the first contiguous block only - so if you're going to call DecommitBlock, you should do it pretty shortly after calling GetContiguousBlock. If you pass in asize of greater than the length of the contiguous block, then the entire block is released - but none of the other block (if present) is released at all. This is a deliberate design choice to remind you that there is more than one block and you should act accordingly. (If you really need to be able to discard data from blocks you've not read yet, it's not too difficult to copy the DecommitBlock function and modify it so that it operates on both blocks; just unwrap the if statement, and adjust the size parameter after the first clause. Implementation of this is left as the dreaded youknowwhat).

And that's the Bip-Buffer implementation done. A short example of how to use it is provided below.

#include "BipBuffer.h"

BipBuffer buffer;
SOCKET s;
bool read_EOF;

bool StartUp
{
    // Allocate a buffer 8192 bytes in length
    if (!buffer.AllocateBuffer(8192)) return false;
    readEOF = false;

    s = socket(...

    ... do something else ...
}

void Foo()
{
    _ASSERTE(buffer.IsValid());

    // Reserve as much space as possible in the buffer:

    int space;
    BYTE* pData = buffer.Reserve(GetBufferSize(), space);

    // We now have *space* amount of room to play with.


    if (pData == NULL) return;

    // Obviously we've not emptied the buffer recently

    // because there isn't any room in it if we return.


    // Let's use the buffer!

    int recvcount = recv(s, (char*)pData, space, 0);

    if (recvcount == SOCKET_ERROR) return;
    // heh... that's some kind of error handling...


    // We now have data in the buffer (or, if the

    // connection was gracefully closed, we don't have any)


    buffer.Commit(recvcount);

    if (recvcount == 0) read_EOF = true;

}

void Bar()
{
    _ASSERTE(buffer.IsValid());

    // Let's empty the buffer.


    int allocated;
    BYTE* pData;

    while (pData = buffer.GetContiguousBlock(allocated)
           != NULL)
    {
        // Let's do something with the data.


        fwrite(pData, allocated, 1, outputfile);

        // (again, lousy error handling)


        buffer.DecommitBlock(allocated);
    }
}

代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <malloc.h>
#include "bipbuffer.h"

struct __bipbuffer_info{
unsigned long size_b; //b空间大小
unsigned long size_a; //a空间大小
unsigned long offer_a; //b空间偏移
unsigned long offer_b; //a空间偏移
unsigned long buffer_len; //缓冲区大小
unsigned long offer_reserve;//储存空闲空间偏移
unsigned long size_reserve; //储存空闲空间大小
char *bipbuffer_addr;
};
struct __bipbuffer_info *p_bipbuffer_info = NULL;

/*
 *函数名称：init_bipbuffer_struct
 *函数功能：初始化结构
 *参数说明：size 传值
 *返 回 值：void
 */
static void init_bipbuffer_struct(unsigned long size)
{
//初始化结构
p_bipbuffer_info->size_a = 0;
p_bipbuffer_info->size_b = 0;
p_bipbuffer_info->offer_a = 0;
p_bipbuffer_info->offer_b = 0;
p_bipbuffer_info->offer_reserve = 0;
p_bipbuffer_info->size_reserve = 0;
p_bipbuffer_info->buffer_len = size;
}

/*
 *函数名称：init_bipbuffer
 *函数功能：分配高效两段式循环缓冲区
 *参数说明：size 要分配缓冲区的大小，一般是以页为单位
 *返 回 值：成功返回0，失败返回负数
 */
int init_bipbuffer(unsigned long size)
{
p_bipbuffer_info = (struct __bipbuffer_info *)malloc(sizeof(struct __bipbuffer_info));
if (p_bipbuffer_info == NULL)
return -1;

//分配缓冲区大小
p_bipbuffer_info->bipbuffer_addr = (char*)malloc(size);
if (p_bipbuffer_info->bipbuffer_addr == NULL){
free(p_bipbuffer_info);
p_bipbuffer_info = NULL;
return -2;
}

init_bipbuffer_struct(size);

return 0;
}

/*
 *函数名称：destroy_bipbuffer
 *函数功能：释放缓冲区
 *参数说明：void
 *返 回 值：成功返回0
 */
int destroy_bipbuffer(void)
{
if (p_bipbuffer_info->bipbuffer_addr){
free(p_bipbuffer_info->bipbuffer_addr);
p_bipbuffer_info->bipbuffer_addr = NULL;
}

if (p_bipbuffer_info){
free(p_bipbuffer_info);
p_bipbuffer_info = NULL;
}

return 0;
}

/*
 *函数名称：get_space_after_a
 *函数功能：获得内存块A后空闲缓冲区的大小
 *参数说明：void
 *返 回 值：空闲缓冲区的大小
 */
static unsigned long get_space_after_a(void)
{
return p_bipbuffer_info->buffer_len -
p_bipbuffer_info->offer_a - p_bipbuffer_info->size_a;
}

/*
 *函数名称：get_b_free_space
 *函数功能：获得内存块B空闲缓冲区的大小
 *参数说明：void
 *返 回 值：空闲缓冲区的大小
 */
static unsigned long get_b_free_space(void)
{
return p_bipbuffer_info->offer_a -
p_bipbuffer_info->offer_b - p_bipbuffer_info->size_b;
}

/*
 *函数名称：get_reserve_addr
 *函数功能：获得空闲缓冲区的地址
 *参数说明：want_size：需要的大小，actually_size实际能给出的大小
 *返 回 值：有空闲空间返回地址，没有则返回NULL
 */
static char *get_reserve_addr(unsigned long want_size, unsigned long *actually_size)
{
unsigned long free_space_size;
/*
 We always allocate on B if B exists;
 this means we have two blocks and our buffer is filling.
 */
if (p_bipbuffer_info->size_b)
{
free_space_size = get_b_free_space();
if (free_space_size == 0)
return NULL;

//多余的空间大于需要的空间，说明有多余的空间
if (want_size < free_space_size)
free_space_size = want_size;

p_bipbuffer_info->offer_reserve = free_space_size;
*actually_size = free_space_size;
p_bipbuffer_info->offer_reserve = p_bipbuffer_info->offer_b + p_bipbuffer_info->size_b;
return p_bipbuffer_info->bipbuffer_addr + p_bipbuffer_info->offer_reserve;
}
else
{
/* Block b does not exist, so we can check
 if the space after a is bigger than the space before A,
 and allocate the bigger one.
 */
/*
 如果内存块B不存在，检查空闲空间是否比内存块A大，分配最大的
 */
free_space_size = get_space_after_a();
printf("\nfree space:%ld", free_space_size);
if (free_space_size >= p_bipbuffer_info->offer_a)//内存块A后有更大的空间
{
if (free_space_size == 0)
return NULL;

//如果需要分配的空间小于空闲的空间
if (want_size < free_space_size)
free_space_size = want_size;

p_bipbuffer_info->size_reserve = free_space_size;
*actually_size = free_space_size;
p_bipbuffer_info->offer_reserve = p_bipbuffer_info->offer_a + p_bipbuffer_info->size_a;
return p_bipbuffer_info->bipbuffer_addr + p_bipbuffer_info->offer_reserve;
}
else//空闲空间不够
{
if (p_bipbuffer_info->offer_a == 0)
return NULL;

if (p_bipbuffer_info->offer_a < want_size)
want_size = p_bipbuffer_info->offer_a;

p_bipbuffer_info->size_reserve = want_size;
*actually_size = want_size;
p_bipbuffer_info->offer_reserve = 0;
return p_bipbuffer_info->bipbuffer_addr;
}
}

return NULL;
}

/*
 *函数名称：commit_data
 *函数功能：数据写入后，修改缓冲区的指针
 *参数说明：size：大小
 *返 回 值：void
 */
static void commit_data(unsigned long size)
{
if (size == 0)
{
// decommit any reservation
p_bipbuffer_info->size_reserve = 0;
p_bipbuffer_info->offer_reserve = 0;
return;
}

/* If we try to commit more space than we asked for,
 clip to the size we asked for.
 */
if (size > p_bipbuffer_info->size_reserve)
size = p_bipbuffer_info->size_reserve;

// If we have no blocks being used currently, we create one in A.
if (p_bipbuffer_info->size_a == 0 && p_bipbuffer_info->size_b == 0)
{
p_bipbuffer_info->offer_a = p_bipbuffer_info->offer_reserve;
p_bipbuffer_info->size_a = size;

p_bipbuffer_info->offer_reserve = 0;
p_bipbuffer_info->size_reserve = 0;
return;
}

if (p_bipbuffer_info->offer_reserve ==
p_bipbuffer_info->size_a + p_bipbuffer_info->offer_a)
p_bipbuffer_info->size_a += size;
else
p_bipbuffer_info->size_b += size;

p_bipbuffer_info->offer_reserve = 0;
p_bipbuffer_info->size_reserve = 0;
}

/*
 *函数名称：get_contiguous_block
 *函数功能：获得可读的数据
 *参数说明：size：大小
 *返 回 值：返回可读的首地址
 */
static char *get_contiguous_block(unsigned long *size)
{
if (p_bipbuffer_info->size_a == 0)
{
*size = 0;
return NULL;
}

*size = p_bipbuffer_info->size_a;
return p_bipbuffer_info->bipbuffer_addr + p_bipbuffer_info->offer_a;
}

/*
 *函数名称：commit_block
 *函数功能：数据读出后，修改缓冲区的指针
 *参数说明：size：大小
 *返 回 值：void
 */
static void commit_block(unsigned long size)
{
if (size >= p_bipbuffer_info->size_a)
{
p_bipbuffer_info->offer_a = p_bipbuffer_info->offer_b;
p_bipbuffer_info->size_a = p_bipbuffer_info->size_b;
p_bipbuffer_info->offer_a = 0;
p_bipbuffer_info->size_b = 0;
}
else
{
p_bipbuffer_info->size_a -= size;
p_bipbuffer_info->offer_a += size;
}
}

/*
 *函数名称：get_committed_size
 *函数功能：获得块A和块B的总大小
 *参数说明：void
 *返 回 值：大小
 */
unsigned long get_committed_size(void)
{
return p_bipbuffer_info->size_a + p_bipbuffer_info->size_b;
}

/*
 *函数名称：get_reservation_size
 *函数功能：获得存储的大小
 *参数说明：void
 *返 回 值：大小
 */
unsigned long get_reservation_size(void)
{
return p_bipbuffer_info->size_reserve;
}

/*
 *函数名称：get_buffer_size
 *函数功能：获得整个缓冲区的大小
 *参数说明：void
 *返 回 值：大小
 */
unsigned long get_buffer_size(void)
{
return p_bipbuffer_info->buffer_len;
}

/*
 *函数名称：write_data_to_bipbuffer
 *函数功能: 向缓冲区写入数据
 *参数说明：buff:要写入的数据，size:要写入的大小
 *返 回 值：实际写入的大小
 */
unsigned long write_data_to_bipbuffer(char *buff, unsigned long size)
{
char *data = NULL;
unsigned long actually_size = 0;

data = (char*)get_reserve_addr(size, &actually_size);
if (data != NULL && actually_size > 0)
{
commit_data(actually_size);
memcpy(data, buff,actually_size);
return actually_size;
}

return 0;
}

/*
 *函数名称：read_data_from_bipbuffer
 *函数功能: 从缓冲区读出数据
 *参数说明：buff:要读出的数据，size:要要读出的大小
 *返 回 值：实际读出的大小
 */
unsigned long read_data_from_bipbuffer(char *buff, unsigned long size)
{
char *data = NULL;
unsigned long actually_size = 0;

data = (char *)get_contiguous_block(&actually_size);
if (data !=NULL && actually_size>0)
{
if (actually_size <= size)
size = actually_size;
else
size = size;

commit_block(size);
memcpy(buff, data, size);
memset(data, 0x00, size);
return size;
}

return 0;
}


/***************************************************************
 *
 *for debug
 *2012-03-24
 ****************************************************************/
void printf_memory(void)
{
unsigned long i=0;
char *buff = (char*)p_bipbuffer_info->bipbuffer_addr;
printf("memory:\n");
for (i=0; i<p_bipbuffer_info->buffer_len; i++)
printf("%02X ", buff[i]&0xFF);
printf("\n---------------\n");
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <malloc.h>
#include "bipbuffer.h"

struct __bipbuffer_info{
    unsigned long size_b;       //b空间大小
    unsigned long size_a;       //a空间大小
    unsigned long offer_a;      //b空间偏移
    unsigned long offer_b;      //a空间偏移
    unsigned long buffer_len;   //缓冲区大小
    unsigned long offer_reserve;//储存空闲空间偏移
    unsigned long size_reserve; //储存空闲空间大小
    char *bipbuffer_addr;
};
struct __bipbuffer_info *p_bipbuffer_info = NULL;

/*
 *函数名称：init_bipbuffer_struct
 *函数功能：初始化结构
 *参数说明：size 传值
 *返 回 值：void
 */
static void init_bipbuffer_struct(unsigned long size)
{
    //初始化结构
    p_bipbuffer_info->size_a = 0;
    p_bipbuffer_info->size_b = 0;
    p_bipbuffer_info->offer_a = 0;
    p_bipbuffer_info->offer_b = 0;
    p_bipbuffer_info->offer_reserve = 0;
    p_bipbuffer_info->size_reserve = 0;
    p_bipbuffer_info->buffer_len = size;
}

/*
 *函数名称：init_bipbuffer
 *函数功能：分配高效两段式循环缓冲区
 *参数说明：size 要分配缓冲区的大小，一般是以页为单位
 *返 回 值：成功返回0，失败返回负数
 */
 int init_bipbuffer(unsigned long size)
{
    p_bipbuffer_info = (struct __bipbuffer_info *)malloc(sizeof(struct __bipbuffer_info));
    if (p_bipbuffer_info == NULL)
        return -1;

    //分配缓冲区大小
    p_bipbuffer_info->bipbuffer_addr = (char*)malloc(size);
    if (p_bipbuffer_info->bipbuffer_addr ==  NULL){
        free(p_bipbuffer_info);
        p_bipbuffer_info = NULL;
        return -2;
    }

    init_bipbuffer_struct(size);

    return 0;
}

/*
 *函数名称：destroy_bipbuffer
 *函数功能：释放缓冲区
 *参数说明：void
 *返 回 值：成功返回0
 */
int destroy_bipbuffer(void)
{
    if (p_bipbuffer_info->bipbuffer_addr){
        free(p_bipbuffer_info->bipbuffer_addr);
        p_bipbuffer_info->bipbuffer_addr = NULL;
    }

    if (p_bipbuffer_info){
        free(p_bipbuffer_info);
        p_bipbuffer_info = NULL;
    }

    return 0;
}

/*
 *函数名称：get_space_after_a
 *函数功能：获得内存块A后空闲缓冲区的大小
 *参数说明：void
 *返 回 值：空闲缓冲区的大小
 */
static unsigned long get_space_after_a(void)
{
    return p_bipbuffer_info->buffer_len -
        p_bipbuffer_info->offer_a - p_bipbuffer_info->size_a;
}

/*
 *函数名称：get_b_free_space
 *函数功能：获得内存块B空闲缓冲区的大小
 *参数说明：void
 *返 回 值：空闲缓冲区的大小
 */
static unsigned long get_b_free_space(void)
{
    return p_bipbuffer_info->offer_a -
        p_bipbuffer_info->offer_b - p_bipbuffer_info->size_b;
}

/*
 *函数名称：get_reserve_addr
 *函数功能：获得空闲缓冲区的地址
 *参数说明：want_size：需要的大小，actually_size实际能给出的大小
 *返 回 值：有空闲空间返回地址，没有则返回NULL
 */
static char *get_reserve_addr(unsigned long want_size, unsigned long *actually_size)
{
    unsigned long free_space_size;
    /*
        We always allocate on B if B exists;
        this means we have two blocks and our buffer is filling.
     */
    if (p_bipbuffer_info->size_b)
    {
        free_space_size = get_b_free_space();
        if (free_space_size == 0)
            return NULL;

        //多余的空间大于需要的空间，说明有多余的空间
        if (want_size < free_space_size)
            free_space_size = want_size;

        p_bipbuffer_info->offer_reserve = free_space_size;
        *actually_size = free_space_size;
        p_bipbuffer_info->offer_reserve = p_bipbuffer_info->offer_b + p_bipbuffer_info->size_b;
        return p_bipbuffer_info->bipbuffer_addr + p_bipbuffer_info->offer_reserve;
    }
    else
    {
        /* Block b does not exist, so we can check
           if the space after a is bigger than the space before A,
           and allocate the bigger one.
         */
         /*
            如果内存块B不存在，检查空闲空间是否比内存块A大，分配最大的
         */
        free_space_size = get_space_after_a();
        printf("\nfree space:%ld", free_space_size);
        if (free_space_size >= p_bipbuffer_info->offer_a)//内存块A后有更大的空间
        {
            if (free_space_size == 0)
                return NULL;

            //如果需要分配的空间小于空闲的空间
            if (want_size < free_space_size)
                free_space_size = want_size;

            p_bipbuffer_info->size_reserve = free_space_size;
            *actually_size = free_space_size;
            p_bipbuffer_info->offer_reserve = p_bipbuffer_info->offer_a + p_bipbuffer_info->size_a;
            return p_bipbuffer_info->bipbuffer_addr + p_bipbuffer_info->offer_reserve;
        }
        else//空闲空间不够
        {
            if (p_bipbuffer_info->offer_a == 0)
                return NULL;

            if (p_bipbuffer_info->offer_a < want_size)
                want_size = p_bipbuffer_info->offer_a;

            p_bipbuffer_info->size_reserve = want_size;
            *actually_size = want_size;
            p_bipbuffer_info->offer_reserve = 0;
            return p_bipbuffer_info->bipbuffer_addr;
        }
    }

    return NULL;
}

/*
 *函数名称：commit_data
 *函数功能：数据写入后，修改缓冲区的指针
 *参数说明：size：大小
 *返 回 值：void
 */
static void commit_data(unsigned long size)
{
    if (size == 0)
    {
        // decommit any reservation
        p_bipbuffer_info->size_reserve  = 0;
        p_bipbuffer_info->offer_reserve = 0;
        return;
    }

    /* If we try to commit more space than we asked for,
       clip to the size we asked for.
     */
    if (size > p_bipbuffer_info->size_reserve)
        size = p_bipbuffer_info->size_reserve;

    // If we have no blocks being used currently, we create one in A.
    if (p_bipbuffer_info->size_a == 0 && p_bipbuffer_info->size_b == 0)
    {
        p_bipbuffer_info->offer_a = p_bipbuffer_info->offer_reserve;
        p_bipbuffer_info->size_a = size;

        p_bipbuffer_info->offer_reserve = 0;
        p_bipbuffer_info->size_reserve = 0;
        return;
    }

    if (p_bipbuffer_info->offer_reserve ==
        p_bipbuffer_info->size_a + p_bipbuffer_info->offer_a)
        p_bipbuffer_info->size_a += size;
    else
        p_bipbuffer_info->size_b += size;

    p_bipbuffer_info->offer_reserve = 0;
    p_bipbuffer_info->size_reserve = 0;
}

/*
 *函数名称：get_contiguous_block
 *函数功能：获得可读的数据
 *参数说明：size：大小
 *返 回 值：返回可读的首地址
 */
static char *get_contiguous_block(unsigned long *size)
{
    if (p_bipbuffer_info->size_a == 0)
    {
        *size = 0;
        return NULL;
    }

    *size = p_bipbuffer_info->size_a;
    return p_bipbuffer_info->bipbuffer_addr + p_bipbuffer_info->offer_a;
}

/*
 *函数名称：commit_block
 *函数功能：数据读出后，修改缓冲区的指针
 *参数说明：size：大小
 *返 回 值：void
 */
static void commit_block(unsigned long size)
{
    if (size >= p_bipbuffer_info->size_a)
    {
        p_bipbuffer_info->offer_a = p_bipbuffer_info->offer_b;
        p_bipbuffer_info->size_a = p_bipbuffer_info->size_b;
        p_bipbuffer_info->offer_a = 0;
        p_bipbuffer_info->size_b = 0;
    }
    else
    {
        p_bipbuffer_info->size_a -= size;
        p_bipbuffer_info->offer_a += size;
    }
}

/*
 *函数名称：get_committed_size
 *函数功能：获得块A和块B的总大小
 *参数说明：void
 *返 回 值：大小
 */
unsigned long get_committed_size(void)
{
    return p_bipbuffer_info->size_a + p_bipbuffer_info->size_b;
}

/*
 *函数名称：get_reservation_size
 *函数功能：获得存储的大小
 *参数说明：void
 *返 回 值：大小
 */
unsigned long get_reservation_size(void)
{
    return p_bipbuffer_info->size_reserve;
}

/*
 *函数名称：get_buffer_size
 *函数功能：获得整个缓冲区的大小
 *参数说明：void
 *返 回 值：大小
 */
unsigned long get_buffer_size(void)
{
    return p_bipbuffer_info->buffer_len;
}

/*
 *函数名称：write_data_to_bipbuffer
 *函数功能: 向缓冲区写入数据
 *参数说明：buff:要写入的数据，size:要写入的大小
 *返 回 值：实际写入的大小
 */
unsigned long write_data_to_bipbuffer(char *buff, unsigned long size)
{
    char *data = NULL;
    unsigned long actually_size = 0;

    data = (char*)get_reserve_addr(size, &actually_size);
    if (data != NULL && actually_size > 0)
    {
        commit_data(actually_size);
        memcpy(data, buff,actually_size);
        return actually_size;
    }

    return 0;
}

/*
 *函数名称：read_data_from_bipbuffer
 *函数功能: 从缓冲区读出数据
 *参数说明：buff:要读出的数据，size:要要读出的大小
 *返 回 值：实际读出的大小
 */
unsigned long read_data_from_bipbuffer(char *buff, unsigned long size)
{
    char *data = NULL;
    unsigned long actually_size = 0;

    data = (char *)get_contiguous_block(&actually_size);
    if (data !=NULL && actually_size>0)
    {
        if (actually_size <= size)
            size = actually_size;
        else
            size = size;

        commit_block(size);
        memcpy(buff, data, size);
        memset(data, 0x00, size);
        return size;
    }

    return 0;
}


/***************************************************************
 *
 *for debug
 *2012-03-24
 ****************************************************************/
void printf_memory(void)
{
    unsigned long i=0;
    char *buff = (char*)p_bipbuffer_info->bipbuffer_addr;
    printf("memory:\n");
    for (i=0; i<p_bipbuffer_info->buffer_len; i++)
        printf("%02X ", buff[i]&0xFF);
    printf("\n---------------\n");
}

#ifndef __BIPBUFFER_H_
#define __BIPBUFFER_H_

int init_bipbuffer(unsigned long size);
int destroy_bipbuffer(void);

unsigned long write_data_to_bipbuffer(char *buff, unsigned long size);
unsigned long read_data_from_bipbuffer(char *buff, unsigned long size);

void printf_memory(void);
#endif

#ifndef __BIPBUFFER_H_
#define __BIPBUFFER_H_

int init_bipbuffer(unsigned long size);
int destroy_bipbuffer(void);

unsigned long write_data_to_bipbuffer(char *buff, unsigned long size);
unsigned long read_data_from_bipbuffer(char *buff, unsigned long size);

void printf_memory(void);
#endif

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <string.h>

#include "bipbuffer.h"

#define BUFF_LEN 100
int main(void)
{
char buff[BUFF_LEN];
unsigned long i = 0;
unsigned long size = 0;

if (init_bipbuffer(2*BUFF_LEN) != 0)
{
printf("\nallocate bip buffer err!");
return -1;
}

memset(buff, 0x66, BUFF_LEN);
write_data_to_bipbuffer(buff, BUFF_LEN);

size = read_data_from_bipbuffer(buff, BUFF_LEN/2);
printf("\n have %ld read:", size);
for (i=0; i<size; i++)
printf("%02X ", buff[i]);
printf("\n====================================\n");

memset(buff, 0xFF, BUFF_LEN);
write_data_to_bipbuffer(buff, BUFF_LEN);
write_data_to_bipbuffer(buff, BUFF_LEN/2);

size = read_data_from_bipbuffer(buff, BUFF_LEN);
printf("\n have %ld read:", size);
for (i=0; i<size; i++)
printf("%02X ", buff[i]);
printf("\n====================================\n");


printf("\n\n\n\n");
printf_memory();

fail:
destroy_bipbuffer();
return 0;
}

 

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