boost的asio接收单路大数据量udp包的方法

开发windows客户端接收RTP视频流，当h264视频达到1080P 60fps的时候，按包来调用recvfrom的函数压力比较大，存在丢包的问题，windows的完成端口的性能效果当然可以解决这个问题，而boost的asio在windows上是基于完成端口来开发的，所以采用boost的asio和环形缓冲区的方法，可以解决接收单路大数据量udp包中丢包的问题。

    需要引入的头文件为：

#include "CircledBuffer.h"
#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>

其中CircledBuffer.h是自定义的缓冲区的类，之后会有介绍，boost的两个文件是asio必需的两个文件。

    需要定义的全局变量为：

using boost::asio::ip::udp;
boost::asio::io_service service;
boost::asio::ip::udp::socket sock(service);
boost::asio::ip::udp::endpoint sender_ep;
CircledBuffer readBuffer;
PacketBuffer* packet;

其中io_service是用来标示启动的，后面会调用run。sock和endpoint类似于描述符和sockaddr_in的关系。CircledBuffer和PacketBuffer*，是自定义缓冲区。

主函数为：

int main(int argc, char* argv[]) {
    boost::asio::ip::udp::endpoint ep( boost::asio::ip::address::from_string("192.168.1.206"),
        9002);
    sock.open(ep.protocol());
    sock.set_option(boost::asio::ip::udp::socket::reuse_address(true));
    boost::asio::socket_base::receive_buffer_size recv_option(8*65534);
    sock.set_option(recv_option);
    sock.bind(ep);
    packet = readBuffer.GetLast();
    sock.async_receive_from(boost::asio::buffer(packet->data, packet->bufferSize), sender_ep, &on_read);
    service.run();
}

初始化ep和sock，其中udp接收的数量比较大的话，需要设定receive_buffer_size，然后bind，设置接受buffer为packet。

介绍一下async_receive_from函数，它有三个参数，分别为接收的buffer，远端的ep，注意与本端的ep不同，远端的ep不用初始化设置，再就是buffer收满后的回调函数。

回调函数的内容是：

void on_read(const boost::system::error_code & err, std::size_t
             read_bytes) {
        std::cout << "read: " << read_bytes << std::endl;
        readBuffer.MoveNext();
        packet= readBuffer.GetLast();
        sock.async_receive_from(boost::asio::buffer(packet->data, packet->bufferSize), sender_ep, &on_read);
}

与main函数的接收部分一致，这里用了不断的自身回调，来实现while recvfrom的功能。

补充说一句，用申请好的CircledBuffer，便于后期的多线程或者异步strand的处理，而不阻塞接收。

缓冲区类的代码：

头文件：

#ifndef CIRCLED_BUFFER_H
#define CIRCLED_BUFFER_H

#include <memory.h>
#include <boost/atomic.hpp>
#define CIRCLED_BUFFER_SIZE 300
#define BUFFER_SIZE 2000

struct PacketBuffer
{
    PacketBuffer(){bufferSize=BUFFER_SIZE;dataSize=0;}
    unsigned int bufferSize;
    unsigned int dataSize;
    char data[BUFFER_SIZE];

    PacketBuffer& operator=(PacketBuffer& other)
    {
        memcpy(data,other.data,other.dataSize);
        dataSize = other.dataSize;
        bufferSize = other.bufferSize;
        return *this;
    }
};

class CircledBuffer
{
public:
    CircledBuffer(unsigned int bufSize=CIRCLED_BUFFER_SIZE);
public:
    ~CircledBuffer(void);
    PacketBuffer* GetAt(unsigned int idx){return &packets[idx];}
    PacketBuffer* GetLast()
    {
        return GetAt(writeIndex.load(boost::memory_order_consume));
    };
    void MoveNext()
    {
        unsigned int idx = writeIndex.load(boost::memory_order_relaxed);
        writeIndex.store((idx+1)%bufferSize,boost::memory_order_release);
    };
    unsigned int GetLastIndex(){return writeIndex.load(boost::memory_order_consume);};
    unsigned int GetSize(){return bufferSize;};
protected:
    boost::atomic<unsigned int> writeIndex;
    unsigned int bufferSize;
    PacketBuffer* packets;
};
#endif

缓冲区类的构造函数与析构函数

#include "CircledBuffer.h"

CircledBuffer::CircledBuffer(unsigned int bufSize)
:bufferSize(bufSize),
writeIndex(0)
{
    packets = new PacketBuffer[bufSize];
}

CircledBuffer::~CircledBuffer(void)
{
    delete []packets;
}

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