multi_handle = curl_multi_init();
// 添加到multi stack
curl_multi_add_handle(multi_handle, curl);
int running_handle_count;
while (CURLM_CALL_MULTI_PERFORM == curl_multi_perform(multi_handle, &running_handle_count))
int cccc = 0;
while (running_handle_count)
struct timeval timeout_tv;
timeout_tv.tv_sec = 1;
timeout_tv.tv_usec = 0;
long curl_timeo = -1;
curl_multi_timeout(multi_handle, &curl_timeo);
if(curl_timeo >= 0) {
timeout_tv.tv_sec = curl_timeo / 1000;
if(timeout_tv.tv_sec > 1)
timeout_tv.tv_sec = 1;
timeout_tv.tv_usec = (curl_timeo % 1000) * 1000;
int max_fd = 0;
fd_set fd_read;
fd_set fd_write;
fd_set fd_except;
FD_ZERO(&fd_read);
FD_ZERO(&fd_write);
FD_ZERO(&fd_except);
CURLMcode abc = curl_multi_fdset(multi_handle, &fd_read, &fd_write, &fd_except, &max_fd);//max_fd总返回-1，curl版本号是7.39
int return_code = select(max_fd + 1, &fd_read, &fd_write, &fd_except, &timeout_tv);
if (SOCKET_ERROR == return_code)
//cerr << "select error." << endl;
break;
while (CURLM_CALL_MULTI_PERFORM == curl_multi_perform(multi_handle, &running_handle_count))
//cout << running_handle_count << endl;
max_fd总返回-1，curl版本号是7.39
这是我在GitHub上查到的。
https://github.com/curl/curl/blob/master/docs/examples/fopen.c
第173行。
/* On success the value of maxfd is guaranteed to be >= -1. We call
select(maxfd + 1, ...); specially in case of (maxfd == -1) there are
no fds ready yet so we call select(0, ...) --or Sleep() on Windows--
to sleep 100ms, which is the minimum suggested value in the
curl_multi_fdset() doc. */
成功时，maxfd的值保证>=-1。我们调用select（maxfd + 1，...）;特别是在（maxfd == -1）的情况下，还没有fds就绪，所以我们在Windows上调用select（0，...）或Sleep（）睡眠100ms，这是最小的建议值。 curl_multi_fdset（）doc。
当调用curl_multi_fdset，尽量延迟时间，等待句柄就绪。
注意：第一个
curl_multi_perform放在循环体内。
