c语言libcurl库的异步用法

        multi接口的使用会比easy 接口稍微复杂点，毕竟multi接口是依赖easy接口的，首先粗略的讲下其使用流程：curl_multi _init初始化一个multi curl对象，为了同时进行多个curl的并发访问，我们需要初始化多个easy curl对象，使用curl_easy_setopt进行相关设置，然后调用curl_multi _add_handle把easy curl对象添加到multi curl对象中，添加完毕后执行curl_multi_perform方法进行并发的访问，访问结束后curl_multi_remove_handle移除相关easy curl对象，curl_easy_cleanup清除easy curl对象，最后curl_multi_cleanup清除multi curl对象。

#include <string>
#include <iostream>

#include <curl/curl.h>
#include <sys/time.h>
#include <unistd.h>

using namespace std;

size_t curl_writer(void *buffer, size_t size, size_t count, void * stream)
{
    std::string * pStream = static_cast<std::string *>(stream);
    (*pStream).append((char *)buffer, size * count);

    return size * count;
};

/**
 * 生成一个easy curl对象，进行一些简单的设置操作
 */
CURL * curl_easy_handler(const std::string & sUrl,
                         const std::string & sProxy,
                         std::string & sRsp,
                         unsigned int uiTimeout)
{
    CURL * curl = curl_easy_init();

    curl_easy_setopt(curl, CURLOPT_URL, sUrl.c_str());
    curl_easy_setopt(curl, CURLOPT_NOSIGNAL, 1);

    if (uiTimeout > 0)
    {
        curl_easy_setopt(curl, CURLOPT_TIMEOUT_MS, uiTimeout);
    }
    if (!sProxy.empty())
    {
        curl_easy_setopt(curl, CURLOPT_PROXY, sProxy.c_str());
    }

    // write function //
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, curl_writer);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &sRsp);

    return curl;
}

/**
 * 使用select函数监听multi curl文件描述符的状态
 * 监听成功返回0，监听失败返回-1
 */
int curl_multi_select(CURLM * curl_m)
{
    int ret = 0;

    struct timeval timeout_tv;
    fd_set  fd_read;
    fd_set  fd_write;
    fd_set  fd_except;
    int     max_fd = -1;

    // 注意这里一定要清空fdset,curl_multi_fdset不会执行fdset的清空操作  //
    FD_ZERO(&fd_read);
    FD_ZERO(&fd_write);
    FD_ZERO(&fd_except);

    // 设置select超时时间  //
    timeout_tv.tv_sec = 1;
    timeout_tv.tv_usec = 0;

    // 获取multi curl需要监听的文件描述符集合 fd_set //
    curl_multi_fdset(curl_m, &fd_read, &fd_write, &fd_except, &max_fd);

    /**
     * When max_fd returns with -1,
     * you need to wait a while and then proceed and call curl_multi_perform anyway.
     * How long to wait? I would suggest 100 milliseconds at least,
     * but you may want to test it out in your own particular conditions to find a suitable value.
     */
    if (-1 == max_fd)
    {
        return -1;
    }

    /**
     * 执行监听，当文件描述符状态发生改变的时候返回
     * 返回0，程序调用curl_multi_perform通知curl执行相应操作
     * 返回-1，表示select错误
     * 注意：即使select超时也需要返回0，具体可以去官网看文档说明
     */
    int ret_code = ::select(max_fd + 1, &fd_read, &fd_write, &fd_except, &timeout_tv);
    switch(ret_code)
    {
    case -1:
        /* select error */
        ret = -1;
        break;
    case 0:
        /* select timeout */
    default:
        /* one or more of curl's file descriptors say there's data to read or write*/
        ret = 0;
        break;
    }

    return ret;
}

#define MULTI_CURL_NUM 3

// 这里设置你需要访问的url //
std::string     URL     = "http://website.com";
// 这里设置代理ip和端口  //
std::string     PROXY   = "ip:port";
// 这里设置超时时间  //
unsigned int    TIMEOUT = 2000; /* ms */

/**
 * multi curl使用demo
 */
int curl_multi_demo(int num)
{
    // 初始化一个multi curl 对象 //
    CURLM * curl_m = curl_multi_init();

    std::string     RspArray[num];
    CURL *          CurlArray[num];

    // 设置easy curl对象并添加到multi curl对象中  //
    for (int idx = 0; idx < num; ++idx)
    {
        CurlArray[idx] = NULL;
        CurlArray[idx] = curl_easy_handler(URL, PROXY, RspArray[idx], TIMEOUT);
        if (CurlArray[idx] == NULL)
        {
            return -1;
        }
        curl_multi_add_handle(curl_m, CurlArray[idx]);
    }

    /*
     * 调用curl_multi_perform函数执行curl请求
     * url_multi_perform返回CURLM_CALL_MULTI_PERFORM时，表示需要继续调用该函数直到返回值不是CURLM_CALL_MULTI_PERFORM为止
     * running_handles变量返回正在处理的easy curl数量，running_handles为0表示当前没有正在执行的curl请求
     */
    int running_handles;
    while (CURLM_CALL_MULTI_PERFORM == curl_multi_perform(curl_m, &running_handles))
    {
        cout << running_handles << endl;
    }

    /**
     * 为了避免循环调用curl_multi_perform产生的cpu持续占用的问题，采用select来监听文件描述符
     */
    while (running_handles)
    {
        if (-1 == curl_multi_select(curl_m))
        {
            cerr << "select error" << endl;
            break;
        } else {
            // select监听到事件，调用curl_multi_perform通知curl执行相应的操作 //
            while (CURLM_CALL_MULTI_PERFORM == curl_multi_perform(curl_m, &running_handles))
            {
                cout << "select: " << running_handles << endl;
            }
        }
        cout << "select: " << running_handles << endl;
    }

    // 输出执行结果 //
    int         msgs_left;
    CURLMsg *   msg;
    while((msg = curl_multi_info_read(curl_m, &msgs_left)))
    {
        if (CURLMSG_DONE == msg->msg)
        {
            int idx;
            for (idx = 0; idx < num; ++idx)
            {
                if (msg->easy_handle == CurlArray[idx]) break;
            }

            if (idx == num)
            {
                cerr << "curl not found" << endl;
            } else
            {
                cout << "curl [" << idx << "] completed with status: "
                        << msg->data.result << endl;
                cout << "rsp: " << RspArray[idx] << endl;
            }
        }
    }

    // 这里要注意cleanup的顺序 //
    for (int idx = 0; idx < num; ++idx)
    {
        curl_multi_remove_handle(curl_m, CurlArray[idx]);
    }

    for (int idx = 0; idx < num; ++idx)
    {
        curl_easy_cleanup(CurlArray[idx]);
    }

    curl_multi_cleanup(curl_m);

    return 0;
}

/**
 * easy curl使用demo
 */
int curl_easy_demo(int num)
{
    std::string     RspArray[num];

    for (int idx = 0; idx < num; ++idx)
    {
        CURL * curl = curl_easy_handler(URL, PROXY, RspArray[idx], TIMEOUT);
        CURLcode code = curl_easy_perform(curl);
        cout << "curl [" << idx << "] completed with status: "
                << code << endl;
        cout << "rsp: " << RspArray[idx] << endl;

        // clear handle //
        curl_easy_cleanup(curl);
    }

    return 0;
}

#define USE_MULTI_CURL

struct timeval begin_tv, end_tv;

int main(int argc, char * argv[])
{
    if (argc < 2)
    {
        return -1;
    }
    int num = atoi(argv[1]);

    // 获取开始时间 //
    gettimeofday(&begin_tv, NULL);
#ifdef USE_MULTI_CURL
    // 使用multi接口进行访问 //
    curl_multi_demo(num);
#else
    // 使用easy接口进行访问 //
    curl_easy_demo(num);
#endif
    // 获取结束时间  //
    struct timeval end_tv;
    gettimeofday(&end_tv, NULL);

    // 计算执行延时并输出，用于比较  //
    int eclapsed = (end_tv.tv_sec - begin_tv.tv_sec) * 1000 +
                   (end_tv.tv_usec - begin_tv.tv_usec) / 1000;

    cout << "eclapsed time:" << eclapsed << "ms" << endl;

    return 0;
}

转载自: http://blog.csdn.net/zxgfa/article/details/8220724