基础组件（线程池、内存池、异步请求池、Mysql连接池）

1、概述

池化技术，减少了资源创建次数，提高了程序响应性能，特别是在高并发场景下，当程序7*24小时运行，创建资源可能会出现耗时较长和失败等问题，池化技术，主要是程序初始化之前创建多个可用连接，集中管理起来，后续直接使用，使用完并归还。

2、线程池

线程池主要解决问题：
1、解决线程创建和消耗所浪费的资源和时间
2、控制线程数量，减少资源竞争

代码解读

一共由三个接口组成：
1、CreatePthreadPool创建工作线程
初始化线程池结构下的条件变量和互斥锁，创建多个线程通过头插法，插入到线程池结构worker成员中
2、thread_func线程入口函数
进入while循环，第一件事先拿锁，然后再去判断，任务队列中是否有数据，要是没有则进入循环中的条件等待，进入条件等待会先释放锁，所以初始化完成之后所有线程全部都会进入条件等待，然后一旦条件满足则会去拿锁。
3、threadPoolQueue将任务加入到任务链表中
先加锁，然后通过头插法插入到线程池结构中的wait_jobs成员中，通知条件变量，然后解锁
4、threadPoolShutdown回收线程池中线程
将工作线程中的标识位全部置为一，然后通知所有线程，然后等待回收所有线程并释放每个节点

总结

线程池就是一个很典型的生产者消费者模型，不断地向任务队列中投放任务，工作线程不断地去队伍队列中去取任务消费掉。

#include 
#include 
#include 
#include 
#include 

#define LL_ADD(item, list) do { 	\
	item->prev = NULL;				\
	item->next = list;				\
	list = item;					\
} while(0)

#define LL_REMOVE(item, list) do {						\
	if (item->prev != NULL) item->prev->next = item->next;	\
	if (item->next != NULL) item->next->prev = item->prev;	\
	if (list == item) list = item->next;					\
	item->prev = item->next = NULL;							\
} while(0)

// 工作线程结构体
typedef struct NWORKER{
    pthread_t id;               // 线程id
    int terminate;              // 终止条件
    struct NTHREADPOLL *worqueue;
    struct NWORKER *prev;       // 前向指针
    struct NWORKER *next;       // 后项指针
}nWorker;

// 任务队列
typedef struct NJOB{
    void (*job_function)(struct NJOB* job);
    void* user_data;
    struct NJOB *prev;
    struct NJOB *next;
}nJob;

typedef struct NTHREADPOLL{
    struct NWORKER *workers;
    struct NJOB *wait_jobs;

    pthread_cond_t cond;
    pthread_mutex_t mtx;
}nThreadpoll;

// 操作线程池函数
#define MAX_PTHREAD 80
#define MAX_JOB 8

// 毁掉函数
void job_fun(nJob *job){
    if(job == NULL) return;
    int *data = (int*)job->user_data;
    printf("user_data:%d-thread_id:%ld,line:%d\n",*data,pthread_self(),__LINE__);

    free(job->user_data);
    job->user_data = NULL;
    free(job);
    job = NULL;
    return;
}

// 线程入口函数
void* thread_func(void* data){
    nWorker *worker = (nWorker*)data;
    while (1)
    {
        pthread_mutex_lock(&(worker->worqueue->mtx));
        while(worker->worqueue->wait_jobs == NULL){
            if(worker->terminate) break;
            pthread_cond_wait(&(worker->worqueue->cond),&(worker->worqueue->mtx));
        }
        if(worker->terminate){
            pthread_mutex_unlock(&(worker->worqueue->mtx));
            break;
        }
        nJob *job = worker->worqueue->wait_jobs;
        if(job != NULL)
            LL_REMOVE(job,worker->worqueue->wait_jobs);
        pthread_mutex_unlock(&(worker->worqueue->mtx));
        if(job == NULL) continue;
        job->job_function(job);
    }
    // free(worker);
    // worker = NULL;
    pthread_exit(0);
}

// 创造线程
int CreatePthreadPool(nThreadpoll* threadpoll,int max_pthread)
{
    if(max_pthread <= 0) max_pthread = MAX_PTHREAD;
    memset(threadpoll,0x00,sizeof(nThreadpoll));
    
	pthread_cond_t blank_cond = PTHREAD_COND_INITIALIZER;
	memcpy(&threadpoll->cond, &blank_cond, sizeof(threadpoll->cond));
	
	pthread_mutex_t blank_mutex = PTHREAD_MUTEX_INITIALIZER;
	memcpy(&threadpoll->mtx, &blank_mutex, sizeof(threadpoll->mtx));
    int i;
    for(i=0; i<max_pthread; i++){
         
        nWorker *worker = (nWorker*)malloc(sizeof(nWorker));
        if(worker == NULL){
            perror("threadpoll->workers");
            return -1;
        }
        memset(worker,0x00,sizeof(nWorker));
        worker->worqueue = threadpoll;
        worker->terminate = 0;
        int ret = pthread_create(&(worker->id),NULL,thread_func,(void*)worker);
        if(ret != 0){
            perror("pthread_create");
            free(worker);
            worker = NULL;
            return -1;
        }
        LL_ADD(worker,worker->worqueue->workers);
    }
    return 0;
}

// 向线程中添加任务，唤醒一个线程去处理
void threadPoolQueue(nThreadpoll* threadpool,nJob *job){
    pthread_mutex_lock(&(threadpool->mtx));
    
    LL_ADD(job,threadpool->wait_jobs);
    
    pthread_cond_signal(&(threadpool->cond));
    pthread_mutex_unlock(&(threadpool->mtx));
    return;
}

void threadPoolShutdown(nThreadpoll *workerqueue){
    nWorker *woker = NULL;
    for(woker = workerqueue->workers;woker!=NULL;woker = woker->next){
        woker->terminate = 1;
    }
	pthread_cond_broadcast(&workerqueue->cond);
    struct NWORKER *tmp = workerqueue->workers;
    while (tmp)
    {
        pthread_join(tmp->id,NULL);
        if(tmp){
            free(tmp);
            tmp = NULL;
        }
        tmp = tmp->next;
    }
    pthread_cond_destroy(&workerqueue->cond);
    pthread_mutex_destroy(&workerqueue->mtx);
    workerqueue->workers = NULL;
	workerqueue->wait_jobs = NULL;
}

int main(){
    nThreadpoll workerQueue;
    if(CreatePthreadPool(&workerQueue,MAX_PTHREAD) != 0){
        perror("CreatePthreadPool faile");
        return -1;
    }
    int i;
    for(i=0;i<MAX_JOB;i++){
        nJob *job = (nJob*)malloc(sizeof(nJob));
        if(job == NULL){
            perror("nJob malloc faile");
            exit(-1);
        }
        job->job_function = job_fun;
        job->user_data = (int*)malloc(sizeof(int));
        *(int*)job->user_data = i;
        threadPoolQueue(&workerQueue,job);
    }
    getchar();
    return 0;
}

2、异步请求池

当我们向数据库或者DNS服务器发送请求时，需要同步等待他的返回结果，这个过程是比较耗时的，所以衍生出异步发起请求，当发出请求之后，不等待请求的响应，而是通过一个线程去监听，主线程去做其他事情，当请求响应之后如何去做其他事情。

同步向DNS服务器发送请求

#include 
#include 
#include 
#include 

#include 
#include 

#include 
#include 
#include 

#include 
#include 
#include 

#include 


#define DNS_SVR				"114.114.114.114"


#define DNS_HOST			0x01
#define DNS_CNAME			0x05



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"
};



int main(int argc, char *argv[]) {

	int count = sizeof(domain) / sizeof(domain[0]);
	int i = 0;

	for (i = 0;i < count;i ++) {
		dns_client_commit(domain[i]);
	}

	getchar();
	
}

异步发送请求

1、dns_async_client_init初始化函数
创建epoll、创建线程，用来监控dns的响应消息
2、dns_async_client_commit创建连接，发送请求，将fd加入到epoll中进行监听
3、dns_async_client_proc线程入口函数
通过epoll_wait进行监听，调用取出数据，调用对应的回调函数，epoll_ctl删除节点。

#include 
#include 
#include 
#include 

#include 
#include 

#include 
#include 
#include 

#include 
#include 
#include 

#include 


#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
	
}

3、内存池

内存池主要是解决，频繁开辟和释放内存，造成的内存碎片问题，大量的内存碎片，会导致我们分配内存失败。
内存池是通过，申请比较大的内存块，后面慢慢的去使用他，避免重复申请和释放内存带来的效率消耗和大量内存碎片

#include 
#include 
#include 
#include 

#include 



#define MP_ALIGNMENT       		32
#define MP_PAGE_SIZE			4096
#define MP_MAX_ALLOC_FROM_POOL	(MP_PAGE_SIZE-1)

#define mp_align(n, alignment) (((n)+(alignment-1)) & ~(alignment-1))
#define mp_align_ptr(p, alignment) (void *)((((size_t)p)+(alignment-1)) & ~(alignment-1))





struct mp_large_s {
	struct mp_large_s *next;
	void *alloc;
};

struct mp_node_s {

	unsigned char *last;
	unsigned char *end;
	
	struct mp_node_s *next;
	size_t failed;
};

struct mp_pool_s {

	size_t max;

	struct mp_node_s *current;
	struct mp_large_s *large;

	struct mp_node_s head[0];

};

struct mp_pool_s *mp_create_pool(size_t size);
void mp_destory_pool(struct mp_pool_s *pool);
void *mp_alloc(struct mp_pool_s *pool, size_t size);
void *mp_nalloc(struct mp_pool_s *pool, size_t size);
void *mp_calloc(struct mp_pool_s *pool, size_t size);
void mp_free(struct mp_pool_s *pool, void *p);


struct mp_pool_s *mp_create_pool(size_t size) {

	struct mp_pool_s *p;
	int ret = posix_memalign((void **)&p, MP_ALIGNMENT, size + sizeof(struct mp_pool_s) + sizeof(struct mp_node_s));
	if (ret) {
		return NULL;
	}
	
	p->max = (size < MP_MAX_ALLOC_FROM_POOL) ? size : MP_MAX_ALLOC_FROM_POOL;
	p->current = p->head;
	p->large = NULL;

	p->head->last = (unsigned char *)p + sizeof(struct mp_pool_s) + sizeof(struct mp_node_s);
	p->head->end = p->head->last + size;

	p->head->failed = 0;

	return p;

}

void mp_destory_pool(struct mp_pool_s *pool) {

	struct mp_node_s *h, *n;
	struct mp_large_s *l;

	for (l = pool->large; l; l = l->next) {
		if (l->alloc) {
			free(l->alloc);
		}
	}

	h = pool->head->next;

	while (h) {
		n = h->next;
		free(h);
		h = n;
	}

	free(pool);

}

void mp_reset_pool(struct mp_pool_s *pool) {

	struct mp_node_s *h;
	struct mp_large_s *l;

	for (l = pool->large; l; l = l->next) {
		if (l->alloc) {
			free(l->alloc);
		}
	}

	pool->large = NULL;

	for (h = pool->head; h; h = h->next) {
		h->last = (unsigned char *)h + sizeof(struct mp_node_s);
	}

}

static void *mp_alloc_block(struct mp_pool_s *pool, size_t size) {

	unsigned char *m;
	struct mp_node_s *h = pool->head;
	size_t psize = (size_t)(h->end - (unsigned char *)h);
	
	int ret = posix_memalign((void **)&m, MP_ALIGNMENT, psize);
	if (ret) return NULL;

	struct mp_node_s *p, *new_node, *current;
	new_node = (struct mp_node_s*)m;

	new_node->end = m + psize;
	new_node->next = NULL;
	new_node->failed = 0;

	m += sizeof(struct mp_node_s);
	m = mp_align_ptr(m, MP_ALIGNMENT);
	new_node->last = m + size;

	current = pool->current;

	for (p = current; p->next; p = p->next) {
		if (p->failed++ > 4) {
			current = p->next;
		}
	}
	p->next = new_node;

	pool->current = current ? current : new_node;

	return m;

}

static void *mp_alloc_large(struct mp_pool_s *pool, size_t size) {

	void *p = malloc(size);
	if (p == NULL) return NULL;

	size_t n = 0;
	struct mp_large_s *large;
	for (large = pool->large; large; large = large->next) {
		if (large->alloc == NULL) {
			large->alloc = p;
			return p;
		}
		if (n ++ > 3) break;
	}

	large = mp_alloc(pool, sizeof(struct mp_large_s));
	if (large == NULL) {
		free(p);
		return NULL;
	}

	large->alloc = p;
	large->next = pool->large;
	pool->large = large;

	return p;
}

void *mp_memalign(struct mp_pool_s *pool, size_t size, size_t alignment) {

	void *p;
	
	int ret = posix_memalign(&p, alignment, size);
	if (ret) {
		return NULL;
	}

	struct mp_large_s *large = mp_alloc(pool, sizeof(struct mp_large_s));
	if (large == NULL) {
		free(p);
		return NULL;
	}

	large->alloc = p;
	large->next = pool->large;
	pool->large = large;

	return p;
}




void *mp_alloc(struct mp_pool_s *pool, size_t size) {

	unsigned char *m;
	struct mp_node_s *p;

	if (size <= pool->max) {

		p = pool->current;

		do {
			
			m = mp_align_ptr(p->last, MP_ALIGNMENT);
			if ((size_t)(p->end - m) >= size) {
				p->last = m + size;
				return m;
			}
			p = p->next;
		} while (p);

		return mp_alloc_block(pool, size);
	}

	return mp_alloc_large(pool, size);
	
}


void *mp_nalloc(struct mp_pool_s *pool, size_t size) {

	unsigned char *m;
	struct mp_node_s *p;

	if (size <= pool->max) {
		p = pool->current;

		do {
			m = p->last;
			if ((size_t)(p->end - m) >= size) {
				p->last = m+size;
				return m;
			}
			p = p->next;
		} while (p);

		return mp_alloc_block(pool, size);
	}

	return mp_alloc_large(pool, size);
	
}

void *mp_calloc(struct mp_pool_s *pool, size_t size) {

	void *p = mp_alloc(pool, size);
	if (p) {
		memset(p, 0, size);
	}

	return p;
	
}

void mp_free(struct mp_pool_s *pool, void *p) {

	struct mp_large_s *l;
	for (l = pool->large; l; l = l->next) {
		if (p == l->alloc) {
			free(l->alloc);
			l->alloc = NULL;

			return ;
		}
	}
	
}


int main(int argc, char *argv[]) {

	int size = 1 << 12;

	struct mp_pool_s *p = mp_create_pool(size);

	int i = 0;
	for (i = 0;i < 10;i ++) {

		void *mp = mp_alloc(p, 512);
//		mp_free(mp);
	}

	//printf("mp_create_pool: %ld\n", p->max);
	printf("mp_align(123, 32): %d, mp_align(17, 32): %d\n", mp_align(24, 32), mp_align(17, 32));
	//printf("mp_align_ptr(p->current, 32): %lx, p->current: %lx, mp_align(p->large, 32): %lx, p->large: %lx\n", mp_align_ptr(p->current, 32), p->current, mp_align_ptr(p->large, 32), p->large);

	int j = 0;
	for (i = 0;i < 5;i ++) {

		char *pp = mp_calloc(p, 32);
		for (j = 0;j < 32;j ++) {
			if (pp[j]) {
				printf("calloc wrong\n");
			}
			printf("calloc success\n");
		}
	}

	//printf("mp_reset_pool\n");

	for (i = 0;i < 5;i ++) {
		void *l = mp_alloc(p, 8192);
		mp_free(p, l);
	}

	mp_reset_pool(p);

	//printf("mp_destory_pool\n");
	for (i = 0;i < 58;i ++) {
		mp_alloc(p, 256);
	}

	mp_destory_pool(p);

	return 0;

}

4、mysql连接池

池化技术能够减少资源创建和释放次数，提高程序的响应性能，特别是在高并发下这种提高更加明显。
1、对象创建时间长。
2、对象创建需要大量资源。
3、对象创建后可被重复使用

4.1、什么是数据库连接池

数据库连接池，是程序启动建立足够多的数据库连接，并将这些连接组成一个连接池，由程序动态地申请和释放

4.2、 连接池和线程池的关系

线程池是主动执行任务，连接池被动操作，池对象被任务获取，任务执行完后归还。
连接池和线程池设置数量的关系：
1、一般线程池线程数量和连接池连接对象数量一致；
2、一般线程执行任务完毕的时候归还连接对象；

头文件DBPool.h

CDBConn类主要是操作mysql数据库：
1、Init从连接池类中获取mysql信息，进行数据库连接
2、ExecuteCreate执行sql语句
3、ExecuteDrop执行sql语句
4、ExecuteQuery执行查询语句
CDBPool类，主要是管理队列中的CDBConn类：
1、构造函数中初始化变量
2、Init创建最小连接数量CDBConn对象存放到队列中m_free_list
3、GetDBConn从连接池中获取一个连接
4、RelDBConn归还连接到队列中

#ifndef DBPOOL_H_
#define DBPOOL_H_

#include 
#include 
#include 
#include 
#include 
#include 

#include 

#define MAX_ESCAPE_STRING_LEN	10240

using namespace std;

// 返回结果 select的时候用
class CResultSet {
public:
	CResultSet(MYSQL_RES* res);
	virtual ~CResultSet();

	bool Next();
	int GetInt(const char* key);
	char* GetString(const char* key);
private:
	int _GetIndex(const char* key);

	MYSQL_RES* 			m_res;
	MYSQL_ROW			m_row;
	map<string, int>	m_key_map;
};

// 插入数据用
class CPrepareStatement {
public:
	CPrepareStatement();
	virtual ~CPrepareStatement();

	bool Init(MYSQL* mysql, string& sql);

	void SetParam(uint32_t index, int& value);
	void SetParam(uint32_t index, uint32_t& value);
    void SetParam(uint32_t index, string& value);
    void SetParam(uint32_t index, const string& value);

	bool ExecuteUpdate();
	uint32_t GetInsertId();
private:
	MYSQL_STMT*	m_stmt;
	MYSQL_BIND*	m_param_bind;
	uint32_t	m_param_cnt;
};

class CDBPool;

class CDBConn {
public:
	CDBConn(CDBPool* pDBPool);
	virtual ~CDBConn();
	int Init();

	// 创建表
	bool ExecuteCreate(const char* sql_query);
	// 删除表
	bool ExecuteDrop(const char* sql_query);
	// 查询
	CResultSet* ExecuteQuery(const char* sql_query);

    /**
    *  执行DB更新，修改
    *
    *  @param sql_query     sql
    *  @param care_affected_rows  是否在意影响的行数，false:不在意；true:在意
    *
    *  @return 成功返回true 失败返回false
    */
	bool ExecuteUpdate(const char* sql_query, bool care_affected_rows = true);
	uint32_t GetInsertId();

	// 开启事务
	bool StartTransaction();
	// 提交事务
	bool Commit();
	// 回滚事务
	bool Rollback();
	// 获取连接池名
	const char* GetPoolName();
	MYSQL* GetMysql() { return m_mysql; }
private:
	CDBPool* 	m_pDBPool;	// to get MySQL server information
	MYSQL* 		m_mysql;	// 对应一个连接
	char		m_escape_string[MAX_ESCAPE_STRING_LEN + 1];
};

class CDBPool {	// 只是负责管理连接CDBConn，真正干活的是CDBConn
public:
	CDBPool() {}
	CDBPool(const char* pool_name, const char* db_server_ip, uint16_t db_server_port,
			const char* username, const char* password, const char* db_name, 
			int max_conn_cnt);
	virtual 	~CDBPool();

	int 		Init();		// 连接数据库，创建连接
	CDBConn* 	GetDBConn(const int timeout_ms = 0);	// 获取连接资源
	void 		RelDBConn(CDBConn* pConn);	// 归还连接资源

	const char* GetPoolName() { return m_pool_name.c_str(); }
	const char* GetDBServerIP() { return m_db_server_ip.c_str(); }
	uint16_t 	GetDBServerPort() { return m_db_server_port; }
	const char* GetUsername() { return m_username.c_str(); }
	const char* GetPasswrod() { return m_password.c_str(); }
	const char* GetDBName() { return m_db_name.c_str(); }
private:
	string 		m_pool_name;	// 连接池名称
	string 		m_db_server_ip;	// 数据库ip
	uint16_t	m_db_server_port; // 数据库端口
	string 		m_username;  	// 用户名
	string 		m_password;		// 用户密码
	string 		m_db_name;		// db名称
	int			m_db_cur_conn_cnt;	// 当前启用的连接数量
	int 		m_db_max_conn_cnt;	// 最大连接数量
	list<CDBConn*>	m_free_list;	// 空闲的连接

	list<CDBConn*>	m_used_list;		// 记录已经被请求的连接
	std::mutex m_mutex;
    std::condition_variable m_cond_var;
	bool m_abort_request = false;
	// CThreadNotify	m_free_notify;	// 信号量
};

#endif /* DBPOOL_H_ */

cpp文件

#include "DBPool.h"
#include 

#define log_error printf
#define log_warn printf
#define log_info printf
#define MIN_DB_CONN_CNT 1
#define MAX_DB_CONN_FAIL_NUM 10


CResultSet::CResultSet(MYSQL_RES *res)
{
	m_res = res;

	// map table field key to index in the result array
	int num_fields = mysql_num_fields(m_res);
	MYSQL_FIELD *fields = mysql_fetch_fields(m_res);
	for (int i = 0; i < num_fields; i++)
	{
		// 多行
		m_key_map.insert(make_pair(fields[i].name, i));
	}
}

CResultSet::~CResultSet()
{
	if (m_res)
	{
		mysql_free_result(m_res);
		m_res = NULL;
	}
}

bool CResultSet::Next()
{
	m_row = mysql_fetch_row(m_res);
	if (m_row)
	{
		return true;
	}
	else
	{
		return false;
	}
}

int CResultSet::_GetIndex(const char *key)
{
	map<string, int>::iterator it = m_key_map.find(key);
	if (it == m_key_map.end())
	{
		return -1;
	}
	else
	{
		return it->second;
	}
}

int CResultSet::GetInt(const char *key)
{
	int idx = _GetIndex(key);
	if (idx == -1)
	{
		return 0;
	}
	else
	{
		return atoi(m_row[idx]); // 有索引
	}
}

char *CResultSet::GetString(const char *key)
{
	int idx = _GetIndex(key);
	if (idx == -1)
	{
		return NULL;
	}
	else
	{
		return m_row[idx];		// 列
	}
}

/
CPrepareStatement::CPrepareStatement()
{
	m_stmt = NULL;
	m_param_bind = NULL;
	m_param_cnt = 0;
}

CPrepareStatement::~CPrepareStatement()
{
	if (m_stmt)
	{
		mysql_stmt_close(m_stmt);
		m_stmt = NULL;
	}

	if (m_param_bind)
	{
		delete[] m_param_bind;
		m_param_bind = NULL;
	}
}

bool CPrepareStatement::Init(MYSQL *mysql, string &sql)
{
	mysql_ping(mysql);	// 当mysql连接丢失的时候，使用mysql_ping能够自动重连数据库

	//g_master_conn_fail_num ++;
	m_stmt = mysql_stmt_init(mysql);
	if (!m_stmt)
	{
		log_error("mysql_stmt_init failed\n");
		return false;
	}

	if (mysql_stmt_prepare(m_stmt, sql.c_str(), sql.size()))
	{
		log_error("mysql_stmt_prepare failed: %s\n", mysql_stmt_error(m_stmt));
		return false;
	}

	m_param_cnt = mysql_stmt_param_count(m_stmt);
	if (m_param_cnt > 0)
	{
		m_param_bind = new MYSQL_BIND[m_param_cnt];
		if (!m_param_bind)
		{
			log_error("new failed\n");
			return false;
		}

		memset(m_param_bind, 0, sizeof(MYSQL_BIND) * m_param_cnt);
	}

	return true;
}

void CPrepareStatement::SetParam(uint32_t index, int &value)
{
	if (index >= m_param_cnt)
	{
		log_error("index too large: %d\n", index);
		return;
	}

	m_param_bind[index].buffer_type = MYSQL_TYPE_LONG;
	m_param_bind[index].buffer = &value;
}

void CPrepareStatement::SetParam(uint32_t index, uint32_t &value)
{
	if (index >= m_param_cnt)
	{
		log_error("index too large: %d\n", index);
		return;
	}

	m_param_bind[index].buffer_type = MYSQL_TYPE_LONG;
	m_param_bind[index].buffer = &value;
}

void CPrepareStatement::SetParam(uint32_t index, string &value)
{
	if (index >= m_param_cnt)
	{
		log_error("index too large: %d\n", index);
		return;
	}

	m_param_bind[index].buffer_type = MYSQL_TYPE_STRING;
	m_param_bind[index].buffer = (char *)value.c_str();
	m_param_bind[index].buffer_length = value.size();
}

void CPrepareStatement::SetParam(uint32_t index, const string &value)
{
	if (index >= m_param_cnt)
	{
		log_error("index too large: %d\n", index);
		return;
	}

	m_param_bind[index].buffer_type = MYSQL_TYPE_STRING;
	m_param_bind[index].buffer = (char *)value.c_str();
	m_param_bind[index].buffer_length = value.size();
}

bool CPrepareStatement::ExecuteUpdate()
{
	if (!m_stmt)
	{
		log_error("no m_stmt\n");
		return false;
	}

	if (mysql_stmt_bind_param(m_stmt, m_param_bind))
	{
		log_error("mysql_stmt_bind_param failed: %s\n", mysql_stmt_error(m_stmt));
		return false;
	}

	if (mysql_stmt_execute(m_stmt))
	{
		log_error("mysql_stmt_execute failed: %s\n", mysql_stmt_error(m_stmt));
		return false;
	}

	if (mysql_stmt_affected_rows(m_stmt) == 0)
	{
		log_error("ExecuteUpdate have no effect\n");
		return false;
	}

	return true;
}

uint32_t CPrepareStatement::GetInsertId()
{
	return mysql_stmt_insert_id(m_stmt);
}

/
CDBConn::CDBConn(CDBPool *pPool)
{
	m_pDBPool = pPool;
	m_mysql = NULL;
}

CDBConn::~CDBConn()
{
	if (m_mysql)
	{
		mysql_close(m_mysql);
	}
}

int CDBConn::Init()
{
	m_mysql = mysql_init(NULL);	// mysql_标准的mysql c client对应的api
	if (!m_mysql)
	{
		log_error("mysql_init failed\n");
		return 1;
	}

	my_bool reconnect = true;
	mysql_options(m_mysql, MYSQL_OPT_RECONNECT, &reconnect);	// 配合mysql_ping实现自动重连
	mysql_options(m_mysql, MYSQL_SET_CHARSET_NAME, "utf8mb4");	// utf8mb4和utf8区别

	// ip 端口 用户名 密码 数据库名
	if (!mysql_real_connect(m_mysql, m_pDBPool->GetDBServerIP(), m_pDBPool->GetUsername(), m_pDBPool->GetPasswrod(),
							m_pDBPool->GetDBName(), m_pDBPool->GetDBServerPort(), NULL, 0))
	{
		log_error("mysql_real_connect failed: %s\n", mysql_error(m_mysql));
		return 2;
	}

	return 0;
}

const char *CDBConn::GetPoolName()
{
	return m_pDBPool->GetPoolName();
}

bool CDBConn::ExecuteCreate(const char *sql_query)
{
	mysql_ping(m_mysql);
	// mysql_real_query 实际就是执行了SQL
	if (mysql_real_query(m_mysql, sql_query, strlen(sql_query)))
	{
		log_error("mysql_real_query failed: %s, sql: start transaction\n", mysql_error(m_mysql));
		return false;
	}

	return true;
}
bool CDBConn::ExecuteDrop(const char *sql_query)
{
	mysql_ping(m_mysql);	// 如果端开了，能够自动重连

	if (mysql_real_query(m_mysql, sql_query, strlen(sql_query)))
	{
		log_error("mysql_real_query failed: %s, sql: start transaction\n", mysql_error(m_mysql));
		return false;
	}

	return true;
}

CResultSet *CDBConn::ExecuteQuery(const char *sql_query)
{
	mysql_ping(m_mysql);

	if (mysql_real_query(m_mysql, sql_query, strlen(sql_query)))
	{
		log_error("mysql_real_query failed: %s, sql: %s\n", mysql_error(m_mysql), sql_query);
		return NULL;
	}
	// 返回结果
	MYSQL_RES *res = mysql_store_result(m_mysql);	// 返回结果
	if (!res)
	{
		log_error("mysql_store_result failed: %s\n", mysql_error(m_mysql));
		return NULL;
	}

	CResultSet *result_set = new CResultSet(res);	// 存储到CResultSet
	return result_set;
}

/*
1.执行成功，则返回受影响的行的数目，如果最近一次查询失败的话，函数返回 -1

2.对于delete,将返回实际删除的行数.

3.对于update,如果更新的列值原值和新值一样,如update tables set col1=10 where id=1;
id=1该条记录原值就是10的话,则返回0。

mysql_affected_rows返回的是实际更新的行数,而不是匹配到的行数。
*/
bool CDBConn::ExecuteUpdate(const char *sql_query, bool care_affected_rows)
{
	mysql_ping(m_mysql);

	if (mysql_real_query(m_mysql, sql_query, strlen(sql_query)))
	{
		log_error("mysql_real_query failed: %s, sql: %s\n", mysql_error(m_mysql), sql_query);
		//g_master_conn_fail_num ++;
		return false;
	}

	if (mysql_affected_rows(m_mysql) > 0)
	{
		return true;
	}
	else
	{ // 影响的行数为0时
		if (care_affected_rows)
		{ // 如果在意影响的行数时, 返回false, 否则返回true
			log_error("mysql_real_query failed: %s, sql: %s\n\n", mysql_error(m_mysql), sql_query);
			return false;
		}
		else
		{
			log_warn("affected_rows=0, sql: %s\n\n", sql_query);
			return true;
		}
	}
}

// bool CDBConn::ExecuteUpdate2(const char *sql_query, bool care_affected_rows)
// {
// again:  // 不能这么写
// 	if (mysql_real_query(m_mysql, sql_query, strlen(sql_query)))
// 	{
// 		log_error("mysql_real_query failed: %s, sql: %s\n", mysql_error(m_mysql), sql_query);
// 		//g_master_conn_fail_num ++;
// 		return false;
// 	} else {
// 		mysql_ping(m_mysql);
// 		goto again;
// 	}

// 	if (mysql_affected_rows(m_mysql) > 0)
// 	{
// 		return true;
// 	}
// 	else
// 	{ // 影响的行数为0时
// 		if (care_affected_rows)
// 		{ // 如果在意影响的行数时, 返回false, 否则返回true
// 			log_error("mysql_real_query failed: %s, sql: %s\n\n", mysql_error(m_mysql), sql_query);
// 			return false;
// 		}
// 		else
// 		{
// 			log_warn("affected_rows=0, sql: %s\n\n", sql_query);
// 			return true;
// 		}
// 	}
// }

bool CDBConn::StartTransaction()
{
	mysql_ping(m_mysql);

	if (mysql_real_query(m_mysql, "start transaction\n", 17))
	{
		log_error("mysql_real_query failed: %s, sql: start transaction\n", mysql_error(m_mysql));
		return false;
	}

	return true;
}

bool CDBConn::Rollback()
{
	mysql_ping(m_mysql);

	if (mysql_real_query(m_mysql, "rollback\n", 8))
	{
		log_error("mysql_real_query failed: %s, sql: rollback\n", mysql_error(m_mysql));
		return false;
	}

	return true;
}

bool CDBConn::Commit()
{
	mysql_ping(m_mysql);

	if (mysql_real_query(m_mysql, "commit\n", 6))
	{
		log_error("mysql_real_query failed: %s, sql: commit\n", mysql_error(m_mysql));
		return false;
	}

	return true;
}
uint32_t CDBConn::GetInsertId()
{
	return (uint32_t)mysql_insert_id(m_mysql);
}


CDBPool::CDBPool(const char *pool_name, const char *db_server_ip, uint16_t db_server_port,
				 const char *username, const char *password, const char *db_name, int max_conn_cnt)
{
	m_pool_name = pool_name;
	m_db_server_ip = db_server_ip;
	m_db_server_port = db_server_port;
	m_username = username;
	m_password = password;
	m_db_name = db_name;
	m_db_max_conn_cnt = max_conn_cnt;	// 
	m_db_cur_conn_cnt = MIN_DB_CONN_CNT; // 最小连接数量
}

// 释放连接池
CDBPool::~CDBPool()
{
	// lock_guard 构造函数加锁，析构函数解锁
	std::lock_guard<std::mutex> lock(m_mutex);
	m_abort_request = true;
	m_cond_var.notify_all();		// 通知所有在等待的

	for (list<CDBConn *>::iterator it = m_free_list.begin(); it != m_free_list.end(); it++)
	{
		CDBConn *pConn = *it;
		delete pConn;
	}

	m_free_list.clear();
}

int CDBPool::Init()
{
	// 创建固定最小的连接数量
	for (int i = 0; i < m_db_cur_conn_cnt; i++)
	{
		CDBConn *pDBConn = new CDBConn(this);
		int ret = pDBConn->Init();
		if (ret)
		{
			delete pDBConn;
			return ret;
		}

		m_free_list.push_back(pDBConn);
	}

	// log_info("db pool: %s, size: %d\n", m_pool_name.c_str(), (int)m_free_list.size());
	return 0;
}

/*
 *TODO: 增加保护机制，把分配的连接加入另一个队列，这样获取连接时，如果没有空闲连接，
 *TODO: 检查已经分配的连接多久没有返回，如果超过一定时间，则自动收回连接，放在用户忘了调用释放连接的接口
 * timeout_ms默认为 0死等
 * timeout_ms >0 则为等待的时间
 */
int wait_cout = 0;
CDBConn *CDBPool::GetDBConn(const int timeout_ms)
{
	std::unique_lock<std::mutex> lock(m_mutex);
	if(m_abort_request) 
	{
		log_warn("have aboort\n");
		return NULL;
	}

	if (m_free_list.empty())		// 当没有连接可以用时
	{
		// 第一步先检测 当前连接数量是否达到最大的连接数量 
		if (m_db_cur_conn_cnt >= m_db_max_conn_cnt)
		{
			// 如果已经到达了，看看是否需要超时等待
			if(timeout_ms <= 0)		// 死等，直到有连接可以用 或者 连接池要退出
			{
				log_info("wait ms:%d\n", timeout_ms);
				m_cond_var.wait(lock, [this] 
				{
					// log_info("wait:%d, size:%d\n", wait_cout++, m_free_list.size());
					// 当前连接数量小于最大连接数量 或者请求释放连接池时退出
					return (!m_free_list.empty()) | m_abort_request;
				});
			} else {
				// return如果返回 false，继续wait(或者超时),  如果返回true退出wait
				// 1.m_free_list不为空
				// 2.超时退出
				// 3. m_abort_request被置为true，要释放整个连接池
				m_cond_var.wait_for(lock, std::chrono::milliseconds(timeout_ms), [this] {
					// log_info("wait_for:%d, size:%d\n", wait_cout++, m_free_list.size());
					return (!m_free_list.empty()) | m_abort_request;
				});
				// 带超时功能时还要判断是否为空
				if(m_free_list.empty()) 	// 如果连接池还是没有空闲则退出
				{
					return NULL;
				}
			}

			if(m_abort_request) 
			{
				log_warn("have aboort\n");
				return NULL;
			}
		}
		else // 还没有到最大连接则创建连接
		{
			CDBConn *pDBConn = new CDBConn(this);	//新建连接
			int ret = pDBConn->Init();
			if (ret)
			{
				log_error("Init DBConnecton failed\n\n");
				delete pDBConn;
				return NULL;
			}
			else
			{
				m_free_list.push_back(pDBConn);
				m_db_cur_conn_cnt++;
				// log_info("new db connection: %s, conn_cnt: %d\n", m_pool_name.c_str(), m_db_cur_conn_cnt);
			}
		}
	}

	CDBConn *pConn = m_free_list.front();	// 获取连接
	m_free_list.pop_front();	// STL 吐出连接，从空闲队列删除
	// pConn->setCurrentTime();  // 伪代码
	m_used_list.push_back(pConn);		// 

	return pConn;
}

void CDBPool::RelDBConn(CDBConn *pConn)
{
	std::lock_guard<std::mutex> lock(m_mutex);

	list<CDBConn *>::iterator it = m_free_list.begin();
	for (; it != m_free_list.end(); it++)	// 避免重复归还
	{
		if (*it == pConn)	
		{
			break;
		}
	}

	if (it == m_free_list.end())
	{
		m_used_list.remove(pConn);
		m_free_list.push_back(pConn);
		m_cond_var.notify_one();		// 通知取队列
	} else 
	{
		log_error("RelDBConn failed\n");
	}
}
// 遍历检测是否超时未归还
// pConn->isTimeout(); // 当前时间 - 被请求的时间
// 强制回收  从m_used_list 放回 m_free_list

4.3、另外版本mysql连接池

对比上面代码，耦合性更强一点，但是比较好理解一点：
1、init创建多个连接对象，并放入到队列中，初始化信号量为连接数的个数
2、GetConnection从连接池中返回一个连接，先信号量–，然后拿锁，推出链接
3、ReleaseConnection返回一个连接，先拿锁，然后归还连接，然后信号量++
4、GetInstance当前类是一个单例类，用来获取对象

1、锁、条件变量、信号量封装

#ifndef LOCKER_H
#define LOCKER_H

#include 
#include 
#include 

class sem
{
public:
    sem()
    {
        if (sem_init(&m_sem, 0, 0) != 0)
        {
            throw std::exception();
        }
    }
    sem(int num)
    {
        if (sem_init(&m_sem, 0, num) != 0)
        {
            throw std::exception();
        }
    }
    ~sem()
    {
        sem_destroy(&m_sem);
    }
    bool wait()
    {
        return sem_wait(&m_sem) == 0;
    }
    bool post()
    {
        return sem_post(&m_sem) == 0;
    }

private:
    sem_t m_sem;
};
class locker
{
public:
    locker()
    {
        if (pthread_mutex_init(&m_mutex, NULL) != 0)
        {
            throw std::exception();
        }
    }
    ~locker()
    {
        pthread_mutex_destroy(&m_mutex);
    }
    bool lock()
    {
        return pthread_mutex_lock(&m_mutex) == 0;
    }
    bool unlock()
    {
        return pthread_mutex_unlock(&m_mutex) == 0;
    }
    pthread_mutex_t *get()
    {
        return &m_mutex;
    }

private:
    pthread_mutex_t m_mutex;
};
class cond
{
public:
    cond()
    {
        if (pthread_cond_init(&m_cond, NULL) != 0)
        {
            //pthread_mutex_destroy(&m_mutex);
            throw std::exception();
        }
    }
    ~cond()
    {
        pthread_cond_destroy(&m_cond);
    }
    bool wait(pthread_mutex_t *m_mutex)
    {
        int ret = 0;
        //pthread_mutex_lock(&m_mutex);
        ret = pthread_cond_wait(&m_cond, m_mutex);
        //pthread_mutex_unlock(&m_mutex);
        return ret == 0;
    }
    bool timewait(pthread_mutex_t *m_mutex, struct timespec t)
    {
        int ret = 0;
        //pthread_mutex_lock(&m_mutex);
        ret = pthread_cond_timedwait(&m_cond, m_mutex, &t);
        //pthread_mutex_unlock(&m_mutex);
        return ret == 0;
    }
    bool signal()
    {
        return pthread_cond_signal(&m_cond) == 0;
    }
    bool broadcast()
    {
        return pthread_cond_broadcast(&m_cond) == 0;
    }

private:
    //static pthread_mutex_t m_mutex;
    pthread_cond_t m_cond;
};
#endif

2、头文件sql_connection_pool.h

#ifndef _CONNECTION_POOL_
#define _CONNECTION_POOL_

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include "locker.h"
#include "log.h"

using namespace std;

class connection_pool
{
public:
	MYSQL *GetConnection();				 //获取数据库连接
	bool ReleaseConnection(MYSQL *conn); //释放连接
	int GetFreeConn();					 //获取连接
	void DestroyPool();					 //销毁所有连接

	//单例模式
	static connection_pool *GetInstance();

	void init(string url, string User, string PassWord, string DataBaseName, int Port, int MaxConn, int close_log); 

private:
	connection_pool();
	~connection_pool();

	int m_MaxConn;  //最大连接数
	int m_CurConn;  //当前已使用的连接数
	int m_FreeConn; //当前空闲的连接数
	locker lock;
	list<MYSQL *> connList; //连接池
	sem reserve;

public:
	string m_url;			 //主机地址
	string m_Port;		 //数据库端口号
	string m_User;		 //登陆数据库用户名
	string m_PassWord;	 //登陆数据库密码
	string m_DatabaseName; //使用数据库名
	int m_close_log;	//日志开关
};

class connectionRAII{

public:
	connectionRAII(MYSQL **con, connection_pool *connPool);
	~connectionRAII();
	
private:
	MYSQL *conRAII;
	connection_pool *poolRAII;
};

#endif

3、cpp文件

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include "sql_connection_pool.h"

using namespace std;

connection_pool::connection_pool()
{
	m_CurConn = 0;
	m_FreeConn = 0;
}

connection_pool *connection_pool::GetInstance()
{
	static connection_pool connPool;
	return &connPool;
}

//构造初始化
void connection_pool::init(string url, string User, string PassWord, string DBName, int Port, int MaxConn, int close_log)
{
	m_url = url;
	m_Port = Port;
	m_User = User;
	m_PassWord = PassWord;
	m_DatabaseName = DBName;
	m_close_log = close_log;

	for (int i = 0; i < MaxConn; i++)
	{
		MYSQL *con = NULL;
		con = mysql_init(con);

		if (con == NULL)
		{
			LOG_ERROR("MySQL Error");
			exit(1);
		}
		con = mysql_real_connect(con, url.c_str(), User.c_str(), PassWord.c_str(), DBName.c_str(), Port, NULL, 0);

		if (con == NULL)
		{
			LOG_ERROR("MySQL Error");
			exit(1);
		}
		connList.push_back(con);
		++m_FreeConn;
	}

	reserve = sem(m_FreeConn);

	m_MaxConn = m_FreeConn;
}


//当有请求时，从数据库连接池中返回一个可用连接，更新使用和空闲连接数
MYSQL *connection_pool::GetConnection()
{
	MYSQL *con = NULL;

	if (0 == connList.size())
		return NULL;

	reserve.wait();
	
	lock.lock();

	con = connList.front();
	connList.pop_front();

	--m_FreeConn;
	++m_CurConn;

	lock.unlock();
	return con;
}

//释放当前使用的连接
bool connection_pool::ReleaseConnection(MYSQL *con)
{
	if (NULL == con)
		return false;

	lock.lock();

	connList.push_back(con);
	++m_FreeConn;
	--m_CurConn;

	lock.unlock();

	reserve.post();
	return true;
}

//销毁数据库连接池
void connection_pool::DestroyPool()
{

	lock.lock();
	if (connList.size() > 0)
	{
		list<MYSQL *>::iterator it;
		for (it = connList.begin(); it != connList.end(); ++it)
		{
			MYSQL *con = *it;
			mysql_close(con);
		}
		m_CurConn = 0;
		m_FreeConn = 0;
		connList.clear();
	}

	lock.unlock();
}

//当前空闲的连接数
int connection_pool::GetFreeConn()
{
	return this->m_FreeConn;
}

connection_pool::~connection_pool()
{
	DestroyPool();
}

connectionRAII::connectionRAII(MYSQL **SQL, connection_pool *connPool)
{
	*SQL = connPool->GetConnection();
	
	conRAII = *SQL;
	poolRAII = connPool;
}

connectionRAII::~connectionRAII(){
	poolRAII->ReleaseConnection(conRAII);
}

4.4、mysql连接重连机制

1、设置启用（当发现连接断开时的）自动重连
my_bool reconnect = true;
mysql_options(m_mysql, MYSQL_OPT_RECONNECT, &reconnect); // 配合mysql_ping实现自动重连

2、检测连接是否正常
int STDCALL mysql_ping(MYSQL *mysql);
描述：
检查与服务端的连接是否正常。连接断开时，如果自动重新连接功能未被禁用，则尝试重新连接服务
器。该函数可被客户端用来检测闲置许久以后，与服务端的连接是否关闭，如有需要，则重新连接。
返回值：
连接正常，返回0；如有错误发生，则返回非0值。返回非0值并不意味着服务器本身关闭掉，也有可能
是网络原因导致网络不通。

4.5、连接池连接设置数量

连接数 = ((核心数 * 2) + 有效磁盘数)
按照这个公式，即是说你的服务器 CPU 是 4核 i7 的，那连接池连接数大小应该为 ((4*2)+1)=9
这里只是一个经验公式。还要和线程池数量以及具体业务结合在一起。
CPU总核数 = 物理CPU个数 * 每颗物理CPU的核数
总逻辑CPU数 = 物理CPU个数 * 每颗物理CPU的核数 * 超线程数

//  查看CPU信息（型号）
cat /proc/cpuinfo | grep name | cut -f2 -d: | uniq -c

// 查看物理CPU个数
cat /proc/cpuinfo| grep "physical id"| sort| uniq| wc -l

//  查看每个物理CPU中core的个数(即核数)
cat /proc/cpuinfo| grep "cpu cores"| uniq

// 查看逻辑CPU的个数
cat /proc/cpuinfo| grep "processor"| wc -l