异步请求池——池式组件

前言

本文详细介绍异步请求池的实现过程，并使用DNS服务来测试异步请求池的性能。

两个必须牢记心中的概念：

同步：检测IO 与读写IO 在同一个流程里
异步：检测IO 与读写IO 不在同一个流程

同步请求与异步请求的处理流程

同步请求的处理流程我们知道，同步：检测IO 与读写IO 在同一个流程里,那么就意味着，发送消息之后，需要等待返回结果，在结果没有返回之前都在阻塞等待，图中我们发了3次请求，很明显的看出，这三个请求是串行的。都串行了，怎么搞并发呀！下面来看看异步请求。

同步请求与异步请求的差异

很明显，同步需要阻塞等待一个请求的完成，异步不需要。同步是一个线程处理所有请求，异步是两个线程。那么如果请1000个请求需要完成呢？必然不可能采用同步阻塞等待的方案，第1000个请求不得等睡着啊。

设计异步请求池
初步构思
在第三方服务中，连接sockfd都是同步的，也就是说，在同步的流程上，一个连接，可以发多个请求，只不过需要阻塞等待上一条请求返回结果而已。

而异步呢，异步的其中一个线程的任务必然是一直发送请求，那么必然是非阻塞的，那么我们设计一个请求对应一个fd。“池的概念就出来了”，在send之后，我们将fd加入到epoll中，而epoll_wait在哪呢？在另一个线程中，epoll所在的线程就一直检测epoll中是否有fd可读。

说的通俗一点，一个请求send之后，将对应的fd加入到epoll里面，另一个线程在一直epoll_wait()读数据。

四元组 init、commit、callback、destroy

//init
struct async_context *dns_async_client_init(void);

//commit
int dns_async_client_commit(struct async_context *ctx, const char *domain, async_result_cb cb);

//pthread callback
static void *dns_async_client_proc(void *arg);

//destroy
int dns_async_client_destroy(struct async_context *ctx);

init：初始化函数只做三件事

1.calloc()创建上下文结构体
2.epoll_create()创建一个epoll fd 
3.pthread_create()创建一个新线程。

commit：commit函数就是发送请求，它做五件事

1.socket 创建socket 
2.connect连接到第三方服务 
3.encode--->mysql/redis/dns 根据对应的协议将发送的数据封装好 
4.send将数据发送出去 
5.epoll_ctl(ctx->epfd, EPOLL_CTL_ADD, sockfd, &ev);把fd加入到epoll中

pthread callback：创建线程时需要给他传递一个回调函数，它做下面伪代码的事情

while(1){
	nready=epoll_wait()
	for(){
		recv();
		parser();//解析协议
		epoll_ctl(epfd, EPOLL_CTL_DEL, sockfd, NULL);
	}
}

destroy：init创建了什么就销毁什么

1.close(epfd);
2.pthread_cancel(thid);
3.free(ctx);

应用协议DNS异步请求池实现

1. 初始化请求池init

init：初始化函数只做两件事

1.calloc创建上下文结构体
2.epoll_create()创建一个epoll fd 
3.pthread_create()创建一个新线程。

struct async_context {
    int ep_fd;
    pthread_t thread_id;
};
//TODO init
//1.malloc ctx;
//2.epoll_create
//3.pthread_create
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->ep_fd = epfd;
    int ret = pthread_create(&ctx->thread_id, NULL, dns_async_client_proc, ctx);
    if (ret) {
        perror("pthread_create");
        return NULL;
    }
    usleep(1); //child go first
    return ctx;
}

2. 建立连接提交请求commit

commit：commit函数就是发送请求，它做五件事

1.socket 创建socket 
2.connect连接到第三方服务 
3.encode--->mysql/redis/dns 根据对应的协议将发送的数据封装好 
4.send将数据发送出去 
5.epoll_ctl(ctx->epfd, EPOLL_CTL_ADD, sockfd, &ev);把fd加入到epoll中

注意这里有一个async_result_cb回调函数，它是负责对fd接收到第三方服务返回的数据之后的回调函数。

//TODO commit
//1.socket
//2.connect
//3.encode ---> redis/mysql/dns
//4.send
//5.epoll_ctl(ctx->ep_fd, EPOLL_CTL_ADD, sockfd, &ev);
int dns_async_client_commit(struct async_context *ctx, const char *domain, async_result_cb cb) {
    //socket
    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);
	//connect
    connect(sockfd, (struct sockaddr *) &dest, sizeof(dest));

	//encode
    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);

    //send
    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;
    ev.events = EPOLLIN;
    //epoll_ctl
    int ret = epoll_ctl(ctx->ep_fd, EPOLL_CTL_ADD, sockfd, &ev);
    return ret;
}

3. epoll线程的回调函数callback

pthread callback：创建线程时需要给他传递一个回调函数，它做下面伪代码的事情

while(1){
	nready=epoll_wait()
	for(){
		recv();
		parser();//解析协议
		epoll_ctl(epfd, EPOLL_CTL_DEL, sockfd, NULL);
	}
}

//TODO pthread callback
/*
 while(1){
    epoll_wait();
    recv;
    parser();
    data callback();
    epoll_ctl(ep_fd, EPOLL_CTL_DEL, sockfd, NULL);
    free(date);
 }
 */
static void *dns_async_client_proc(void *arg) {
    struct async_context *ctx = (struct async_context *) arg;
    int epfd = ctx->ep_fd;
    while (1) {
        struct epoll_event events[ASYNC_CLIENT_NUM] = {0};
        int nready = epoll_wait(epfd, events, ASYNC_CLIENT_NUM, -1);
        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);
            //recv
            recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr *) &addr, (socklen_t *) &addr_len);
			//parse
            struct dns_item *domain_list = NULL;
            int count = dns_parse_response(buffer, &domain_list);
            //call cb
            data->cb(domain_list, count);
            //del
            epoll_ctl(epfd, EPOLL_CTL_DEL, sockfd, NULL);
            close(sockfd);
            //free
            dns_async_client_free_domains(domain_list, count);
            free(data);
        }
    }
}

4. 销毁请求池destroy

destroy：init创建了什么就销毁什么

1.close(epfd);
2.pthread_cancel(thid);
3.free(ctx);

//TODO destroy
//1.close(ep_fd)
//2.pthread_cancel(ctx->thread_id);
//3.free(ctx);
int dns_async_client_destroy(struct async_context *ctx) {
    close(ctx->ep_fd);
    pthread_cancel(ctx->thread_id);
    free(ctx);
    return 0;
}

Demo完整代码

DNS同步请求代码

#include <stdio.h>
#include <stdlib.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 <pthread.h>

#define DNS_SVR                "114.114.114.114"
#define DNS_HOST            0x01
#define DNS_CNAME            0x05

// DNS报文头部
struct dns_header {
    unsigned short id;
    unsigned short flags;
    unsigned short qdcount;
    unsigned short ancount;
    unsigned short nscount;
    unsigned short arcount;
};
// DNS报文正文
struct dns_question {
    int length;
    unsigned short qtype;
    unsigned short qclass;
    char *qname;
};
// DNS服务器返回的ip信息
struct dns_item {
    char *domain;
    char *ip;
};

// header填充与函数实现
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;
}

// question填充与函数实现
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;
}

// 对头部和问题区做一个打包
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;
}

// 解析服务器发过来的数据
static int is_pointer(int in) {
    return ((in & 0xC0) == 0xC0);
}


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;
            }
        }
    }
}

//解析响应信息	buffer为response返回的信息
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);

    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));

    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);

    printf("recvfrom n : %d\n", n);
    struct dns_item *domains = NULL;
    dns_parse_response(buffer, &domains);

    return 0;
}

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"
};


int main(int argc, char *argv[]) {
    int begin, end;
    begin = clock();    //计时开始

    int i;
    for (i = 0; i < sizeof(domain) / sizeof(domain[0]); i++) {
        dns_client_commit(domain[i]);
    }

    end = clock();    //计时结束

    getchar();

    printf("\n\nRunning Time：%lfs\n", (double)(end-begin)/CLOCKS_PER_SEC);
}