当服务器运行时，难免会和大量其余中间件（mysql,redis...）或者其他服务器进行连接请求。但是如果每送一次连接，就等待其请求的返回，如下图，难免会造成服务器响应慢，任务堆积的问题，所以为了解决这一问题，可以制作一个异步的连接池！！！
制作思路如下：
1、commit负责发送请求
1)socket
2)connect server
3)encode协议包
4)send
5)fd加入到监听线程的epoll
2、thread监听是否响应
3、init初始化异步请求池
1）epol_create
2) pthread_create
4、destroy回收请求池
//
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/epoll.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <pthread.h>
#define DNS_SVR "114.114.114.114"
#define DNS_HOST 0x01
#define DNS_CNAME 0x05
#define ASYNC_CLIENT_NUM 1024
struct dns_header {
unsigned short id;
unsigned short flags;
unsigned short qdcount;
unsigned short ancount;
unsigned short nscount;
unsigned short arcount;
};
struct dns_question {
int length;
unsigned short qtype;
unsigned short qclass;
char *qname;
};
struct dns_item {
char *domain;
char *ip;
};
typedef void (*async_result_cb)(struct dns_item *list, int count);
struct async_context {
int epfd;
};
struct ep_arg {
int sockfd;
async_result_cb cb;//对于这个fd的回调函数（对不同fd所使用的协议的特定回调函数）
};
int dns_create_header(struct dns_header *header) {
if (header == NULL) return -1;
memset(header, 0, sizeof(struct dns_header));
srandom(time(NULL));
header->id = random();
header->flags |= htons(0x0100);
header->qdcount = htons(1);
return 0;
}
int dns_create_question(struct dns_question *question, const char *hostname) {
if (question == NULL) return -1;
memset(question, 0, sizeof(struct dns_question));
question->qname = (char*)malloc(strlen(hostname) + 2);
if (question->qname == NULL) return -2;
question->length = strlen(hostname) + 2;
question->qtype = htons(1);
question->qclass = htons(1);
const char delim[2] = ".";
char *hostname_dup = strdup(hostname);
char *token = strtok(hostname_dup, delim);
char *qname_p = question->qname;
while (token != NULL) {
size_t len = strlen(token);
*qname_p = len;
qname_p ++;
strncpy(qname_p, token, len+1);
qname_p += len;
token = strtok(NULL, delim);
}
free(hostname_dup);
return 0;
}
int dns_build_request(struct dns_header *header, struct dns_question *question, char *request) {
int header_s = sizeof(struct dns_header);
int question_s = question->length + sizeof(question->qtype) + sizeof(question->qclass);
int length = question_s + header_s;
int offset = 0;
memcpy(request+offset, header, sizeof(struct dns_header));
offset += sizeof(struct dns_header);
memcpy(request+offset, question->qname, question->length);
offset += question->length;
memcpy(request+offset, &question->qtype, sizeof(question->qtype));
offset += sizeof(question->qtype);
memcpy(request+offset, &question->qclass, sizeof(question->qclass));
return length;
}
static int is_pointer(int in) {
return ((in & 0xC0) == 0xC0);
}
static int set_block(int fd, int block) {
int flags = fcntl(fd, F_GETFL, 0);
if (flags < 0) return flags;
if (block) {
flags &= ~O_NONBLOCK;
} else {
flags |= O_NONBLOCK;
}
if (fcntl(fd, F_SETFL, flags) < 0) return -1;
return 0;
}
static void dns_parse_name(unsigned char *chunk, unsigned char *ptr, char *out, int *len) {
int flag = 0, n = 0, alen = 0;
char *pos = out + (*len);
while (1) {
flag = (int)ptr[0];
if (flag == 0) break;
if (is_pointer(flag)) {
n = (int)ptr[1];
ptr = chunk + n;
dns_parse_name(chunk, ptr, out, len);
break;
} else {
ptr ++;
memcpy(pos, ptr, flag);
pos += flag;
ptr += flag;
*len += flag;
if ((int)ptr[0] != 0) {
memcpy(pos, ".", 1);
pos += 1;
(*len) += 1;
}
}
}
}
static int dns_parse_response(char *buffer, struct dns_item **domains) {
int i = 0;
unsigned char *ptr = buffer;
ptr += 4;
int querys = ntohs(*(unsigned short*)ptr);
ptr += 2;
int answers = ntohs(*(unsigned short*)ptr);
ptr += 6;
for (i = 0;i < querys;i ++) {
while (1) {
int flag = (int)ptr[0];
ptr += (flag + 1);
if (flag == 0) break;
}
ptr += 4;
}
char cname[128], aname[128], ip[20], netip[4];
int len, type, ttl, datalen;
int cnt = 0;
struct dns_item *list = (struct dns_item*)calloc(answers, sizeof(struct dns_item));
if (list == NULL) {
return -1;
}
for (i = 0;i < answers;i ++) {
bzero(aname, sizeof(aname));
len = 0;
dns_parse_name(buffer, ptr, aname, &len);
ptr += 2;
type = htons(*(unsigned short*)ptr);
ptr += 4;
ttl = htons(*(unsigned short*)ptr);
ptr += 4;
datalen = ntohs(*(unsigned short*)ptr);
ptr += 2;
if (type == DNS_CNAME) {
bzero(cname, sizeof(cname));
len = 0;
dns_parse_name(buffer, ptr, cname, &len);
ptr += datalen;
} else if (type == DNS_HOST) {
bzero(ip, sizeof(ip));
if (datalen == 4) {
memcpy(netip, ptr, datalen);
inet_ntop(AF_INET , netip , ip , sizeof(struct sockaddr));
printf("%s has address %s\n" , aname, ip);
printf("\tTime to live: %d minutes , %d seconds\n", ttl / 60, ttl % 60);
list[cnt].domain = (char *)calloc(strlen(aname) + 1, 1);
memcpy(list[cnt].domain, aname, strlen(aname));
list[cnt].ip = (char *)calloc(strlen(ip) + 1, 1);
memcpy(list[cnt].ip, ip, strlen(ip));
cnt ++;
}
ptr += datalen;
}
}
*domains = list;
ptr += 2;
return cnt;
}
int dns_client_commit(const char *domain) {
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0) {
perror("create socket failed\n");
exit(-1);
}
printf("url:%s\n", domain);
set_block(sockfd, 0); //nonblock
struct sockaddr_in dest;
bzero(&dest, sizeof(dest));
dest.sin_family = AF_INET;
dest.sin_port = htons(53);
dest.sin_addr.s_addr = inet_addr(DNS_SVR);
int ret = connect(sockfd, (struct sockaddr*)&dest, sizeof(dest));
//printf("connect :%d\n", ret);
struct dns_header header = {0};
dns_create_header(&header);
struct dns_question question = {0};
dns_create_question(&question, domain);
char request[1024] = {0};
int req_len = dns_build_request(&header, &question, request);
int slen = sendto(sockfd, request, req_len, 0, (struct sockaddr*)&dest, sizeof(struct sockaddr));
while (1) {
char buffer[1024] = {0};
struct sockaddr_in addr;
size_t addr_len = sizeof(struct sockaddr_in);
int n = recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr*)&addr, (socklen_t*)&addr_len);
if (n <= 0) continue;
printf("recvfrom n : %d\n", n);
struct dns_item *domains = NULL;
dns_parse_response(buffer, &domains);
break;
}
return 0;
}
void dns_async_client_free_domains(struct dns_item *list, int count) {
int i = 0;
for (i = 0;i < count;i ++) {
free(list[i].domain);
free(list[i].ip);
}
free(list);
}
//dns_async_client_proc()
//epoll_wait
//result callback
static void* dns_async_client_proc(void *arg) {
struct async_context *ctx = (struct async_context*)arg;
int epfd = ctx->epfd;
while (1) {
struct epoll_event events[ASYNC_CLIENT_NUM] = {0};
int nready = epoll_wait(epfd, events, ASYNC_CLIENT_NUM, -1);
if (nready < 0) {
if (errno == EINTR || errno == EAGAIN) {
continue;
} else {
break;
}
} else if (nready == 0) {
continue;
}
printf("nready:%d\n", nready);
int i = 0;
for (i = 0;i < nready;i ++) {
struct ep_arg *data = (struct ep_arg*)events[i].data.ptr;
int sockfd = data->sockfd;
char buffer[1024] = {0};
struct sockaddr_in addr;
size_t addr_len = sizeof(struct sockaddr_in);
int n = recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr*)&addr, (socklen_t*)&addr_len);//对方按照udp的协议回发的
struct dns_item *domain_list = NULL;
int count = dns_parse_response(buffer, &domain_list);
data->cb(domain_list, count); //call cb
int ret = epoll_ctl(epfd, EPOLL_CTL_DEL, sockfd, NULL);
//printf("epoll_ctl DEL --> sockfd:%d\n", sockfd);
close(sockfd); /
dns_async_client_free_domains(domain_list, count);
free(data);
}
}
}
//dns_async_client_init()
//epoll init
//thread init
struct async_context *dns_async_client_init(void) {
int epfd = epoll_create(1); //
if (epfd < 0) return NULL;
struct async_context *ctx = calloc(1, sizeof(struct async_context));
if (ctx == NULL) {
close(epfd);
return NULL;
}
ctx->epfd = epfd;
pthread_t thread_id;
int ret = pthread_create(&thread_id, NULL, dns_async_client_proc, ctx);
if (ret) {
perror("pthread_create");
return NULL;
}
usleep(1); //child go first
return ctx;
}
//dns_async_client_commit(ctx, domain)
//socket init
//dns_request
//sendto dns send
int dns_async_client_commit(struct async_context* ctx, const char *domain, async_result_cb cb) {
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0) {
perror("create socket failed\n");
exit(-1);
}
printf("url:%s\n", domain);
set_block(sockfd, 0); //nonblock
struct sockaddr_in dest;
bzero(&dest, sizeof(dest));
dest.sin_family = AF_INET;
dest.sin_port = htons(53);
dest.sin_addr.s_addr = inet_addr(DNS_SVR);//通过inet_addr()函数将点分式转换为u_long型
int ret = connect(sockfd, (struct sockaddr*)&dest, sizeof(dest));//浏览器向DNS的请求为udp，这是为了保证send的数据能成功传达
//printf("connect :%d\n", ret);
struct dns_header header = {0};
dns_create_header(&header);
struct dns_question question = {0};
dns_create_question(&question, domain);
char request[1024] = {0};
int req_len = dns_build_request(&header, &question, request);
int slen = sendto(sockfd, request, req_len, 0, (struct sockaddr*)&dest, sizeof(struct sockaddr));
struct ep_arg *eparg = (struct ep_arg*)calloc(1, sizeof(struct ep_arg));
if (eparg == NULL) return -1;
eparg->sockfd = sockfd;
eparg->cb = cb;
struct epoll_event ev;
ev.data.ptr = eparg;//把这个fd和这个eparg绑定*****很重要！！！相当于赋予了fd自己的属性
ev.events = EPOLLIN;
ret = epoll_ctl(ctx->epfd, EPOLL_CTL_ADD, sockfd, &ev);//给接收线程添加fd，这个fd绑定了eparg
//printf(" epoll_ctl ADD: sockfd->%d, ret:%d\n", sockfd, ret);
return ret;
}
char *domain[] = {
"www.ntytcp.com",
"bojing.wang",
"www.baidu.com",
"tieba.baidu.com",
"news.baidu.com",
"zhidao.baidu.com",
"music.baidu.com",
"image.baidu.com",
"v.baidu.com",
"map.baidu.com",
"baijiahao.baidu.com",
"xueshu.baidu.com",
"cloud.baidu.com",
"www.163.com",
"open.163.com",
"auto.163.com",
"gov.163.com",
"money.163.com",
"sports.163.com",
"tech.163.com",
"edu.163.com",
"www.taobao.com",
"q.taobao.com",
"sf.taobao.com",
"yun.taobao.com",
"baoxian.taobao.com",
"www.tmall.com",
"suning.tmall.com",
"www.tencent.com",
"www.qq.com",
"www.aliyun.com",
"www.ctrip.com",
"hotels.ctrip.com",
"hotels.ctrip.com",
"vacations.ctrip.com",
"flights.ctrip.com",
"trains.ctrip.com",
"bus.ctrip.com",
"car.ctrip.com",
"piao.ctrip.com",
"tuan.ctrip.com",
"you.ctrip.com",
"g.ctrip.com",
"lipin.ctrip.com",
"ct.ctrip.com"
};
static void dns_async_client_result_callback(struct dns_item *list, int count) {//count是说明接收到了几次
int i = 0;
for (i = 0;i < count;i ++) {
printf("name:%s, ip:%s\n", list[i].domain, list[i].ip);
}
}
int main(int argc, char *argv[]) {
#if 0
dns_client_commit(argv[1]);
#else
struct async_context *ctx = dns_async_client_init();
if (ctx == NULL) return -2;
int count = sizeof(domain) / sizeof(domain[0]);
int i = 0;
for (i = 0;i < count;i ++) {
dns_async_client_commit(ctx, domain[i], dns_async_client_result_callback);
//sleep(2);
}
getchar();
#endif
}
与协程相比较，如果实现相同异步请求池功能，假如100的commit，相当于管理100个协程，而异步连接池的callback的函数就类似协程的调度器。
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参考博客：异步请求池-pudn.com