epoll

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本文介绍了epoll作为Linux 2.6内核中的高效I/O多路复用技术，通过红黑树和双链表的数据结构实现高性能并发处理。通过实例代码详细展示了如何使用epoll监控多个socket的读事件，包括epoll_create、epoll_ctl和epoll_wait三个关键函数的使用。

epoll是linux2.6用于高并发数据处理的接口。

instance analysis1:

send.c

//send.c
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/epoll.h>
#include <arpa/inet.h>

int main()
{

  int sock;
  struct sockaddr_in dest1, dest2;
  char buf[1024];

  sock = socket(AF_INET, SOCK_DGRAM, 0);

  dest1.sin_family = AF_INET;
  dest2.sin_family = AF_INET;

  inet_pton(AF_INET, "127.0.0.1", &dest1.sin_addr.s_addr);
  inet_pton(AF_INET, "127.0.0.1", &dest2.sin_addr.s_addr);

  dest1.sin_port = htons(11111);
  dest2.sin_port = htons(22222);
  int count = 10;
  while(count--)
  {
	  printf("count:%d\n",count);
  strcpy(buf, "data to port 11111\n");
  //给地址1(dest1)送信
  sendto(sock, buf, strlen(buf), 0, (struct sockaddr*)&dest1, sizeof(dest1));
	sleep(1);
  strcpy(buf, "data to port 22222\n");
  //给地址2(dest2)送信
  sendto(sock, buf, strlen(buf), 0, (struct sockaddr*)&dest2, sizeof(dest1));
  
  }

  close(sock);

  return 0;
}

recv.c

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/epoll.h>
#include <arpa/inet.h>

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define EVENTS 12

int main()
{
	int sock1, sock2;
	struct sockaddr_in addr1, addr2;
	int epfd;
	struct epoll_event ev, ev_ret[EVENTS];
	char buf[2048];
	int i;
	int nfds;
	int n;

	//创建2个接受消息的socket
	sock1 = socket(AF_INET, SOCK_DGRAM, 0);
	sock2 = socket(AF_INET, SOCK_DGRAM, 0);
	addr1.sin_family = AF_INET;
	addr2.sin_family = AF_INET;

	inet_pton(AF_INET, "127.0.0.1", &addr1.sin_addr.s_addr);
	inet_pton(AF_INET, "127.0.0.1", &addr2.sin_addr.s_addr);

	addr1.sin_port = htons(11111);
	addr2.sin_port = htons(22222);

	bind(sock1, (struct sockaddr*)&addr1, sizeof(addr1));
	bind(sock2, (struct sockaddr*)&addr2, sizeof(addr2));

	//参数不小于0就行
	epfd = epoll_create(1);
	if(epfd < 0){
		perror("epoll_create");
		return 1;
	}

	memset(&ev, 0, sizeof(ev));
	ev.events = EPOLLIN;//只读
	ev.data.fd = sock1;//把sock1加到epoll
	if(epoll_ctl(epfd, EPOLL_CTL_ADD, sock1, &ev) != 0){
		perror("epoll_ctl");
		return 1;
	}

	memset(&ev, 0, sizeof(ev));
	ev.events = EPOLLIN;//只读
	ev.data.fd = sock2;//把sock2加到epoll
	if(epoll_ctl(epfd, EPOLL_CTL_ADD, sock2, &ev) != 0){
		perror("epoll_ctl");
		return 1;
	}

	while(1)
	{
		printf("before epoll_wait\n");
		//int epoll_wait(int epfd, struct epoll_event *events,int maxevents, int timeout);
		//timeout ms
		//在这里会阻塞，只等待10秒，超过10秒，epoll_wait函数结束，返回0给nfds.
		nfds = epoll_wait(epfd, ev_ret, EVENTS, 10*1000);
		if(nfds < 0)
		{
			perror("epoll_wait; return 1");
			return 1;
		}

		printf("after epoll_wait\n");
		if(nfds == 0)
		{
			printf("timeout....exit\n");
			break;
		}

		printf("runing nfds：%d\n", nfds);

		for(i = 0; i < nfds; ++i)
		{
			//判断进来的socket是哪个socket
			if(ev_ret[i].data.fd == sock1)
			{
				//从sock1读取数据，并写入到标准输出
				n = recv(sock1, buf, sizeof(buf), 0);
				write(fileno(stdout), buf, n);
			}
			//判断进来的socket是哪个socket
			else if(ev_ret[i].data.fd == sock2)
			{
				//从sock1读取数据，并写入到标准输出
				n = recv(sock2, buf, sizeof(buf), 0);
				write(fileno(stdout), buf, n);
			}
		}
	}

	close(sock1);
	close(sock2);
	return 0;
}