引言
我们都知道异步的性能比同步的性能高。
同步和异步的区别
同步：你执行了我再执行。
异步：你不执行我先跳过，干其他的事，等你执行了我再执行。
同步和异步的优缺点
同步：流程控制简单，但是执行效率低
异步：执行效率高，但是流程控制相对复杂
一、同步DNS请求代码示例
功能：同步的方式请求若干个dns的域名解析服务，并打印解析结果。
#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_EVENT_LENGTH 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; }; 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 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); 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" }; struct async_context { int epfd; pthread_t thid; }; struct ep_arg { int sockfd; }; void* dns_async_client_callback(void *arg) { struct async_context *ctx = (struct async_context *)arg; while(1) { struct epoll_event events[ASYNC_EVENT_LENGTH] = {0}; int nready = epoll_wait(ctx->epfd, events, ASYNC_EVENT_LENGTH, -1); if (nready < 0) continue; printf("nready: %d\n", nready); int i = 0; for (i = 0;i < nready;i ++) { //int sockfd = events[i].data.fd; struct ep_arg *arg = (struct ep_arg *)events[i].data.ptr; int sockfd = arg->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); printf("recvfrom n : %d\n", n); struct dns_item *domains = NULL; dns_parse_response(buffer, &domains); epoll_ctl(ctx->epfd, EPOLL_CTL_DEL, sockfd, NULL); close(sockfd); free(arg); } } } // int dns_async_client_destroy(struct async_context *ctx) { // 1 if (ctx == NULL) return -EINVAL; pthread_cancel(ctx->thid); close(ctx->epfd); return 0; } // int dns_async_client_init(struct async_context *ctx) { // 1 if (ctx == NULL) return -EINVAL; ctx->epfd =epoll_create(1); int ret = pthread_create(&ctx->thid, NULL, dns_async_client_callback, ctx); if (ret) { perror("pthread_create"); return -1; } return 0; } int dns_async_client_commit(struct async_context *ctx, 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)); //sendto --> fd struct ep_arg *arg = (struct ep_arg *)calloc(1, sizeof(struct ep_arg)); if (arg == NULL) return -1; struct epoll_event ev; ev.data.ptr = arg; ev.events = EPOLLIN; return epoll_ctl(ctx->epfd, EPOLL_CTL_ADD, sockfd, &ev); } int main(int argc, char *argv[]) { int count = sizeof(domain) / sizeof(domain[0]); int i = 0; #if 0 for (i = 0;i < count;i ++) { dns_client_commit(domain[i]); } #else struct async_context ctx; dns_async_client_init(&ctx); for (i = 0;i < count;i ++) { dns_async_client_commit(&ctx, domain[i]); } #endif getchar(); }
二、异步代码示例
功能：异步的方式请求若干个dns的域名解析服务，并打印解析结果。
#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; }; 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); 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); 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)); 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; ret = epoll_ctl(ctx->epfd, EPOLL_CTL_ADD, sockfd, &ev); //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) { 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 }
运行结果分析：
异步的效率高于同步的方式。
