help: curl_multi_info_read always return NULL

What I did is to make a http2 post request, the code is below:
```
curl_version_info_data *info = curl_version_info(CURLVERSION_NOW);
bool support = (info->features & CURL_VERSION_HTTP2);

//create multi handle
CURLM *multi_handle = curl_multi_init();
//create sub handle
CURL *hnd = curl_easy_init();
curl_easy_setopt(hnd, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
data_chunk_t chunk;
chunk.data = malloc(1); /* will be grown as needed by the realloc above */
chunk.size = 0; /* no data at this point */
curl_easy_setopt(hnd, CURLOPT_WRITEDATA, &chunk);
/* set the same URL */
curl_easy_setopt(hnd, CURLOPT_URL, "ai-test.xfyousheng.com:91");

struct curl_slist* head = NULL;
head = curl_slist_append(head, boundary);
head = curl_slist_append(head, "Content-Disposition: form-data; name=\"metadata\"");
head = curl_slist_append(head, "Content-Type: application/json;charset=UTF-8");
curl_easy_setopt(hnd, CURLOPT_HTTPHEADER, head);
curl_easy_setopt(hnd, CURLOPT_POSTFIELDS, request_json->data);

/* please be verbose */
curl_easy_setopt(hnd, CURLOPT_VERBOSE, 1L);
curl_easy_setopt(hnd, CURLOPT_DEBUGFUNCTION, my_trace);

/* HTTP/2 please */
curl_easy_setopt(hnd, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2_0);

/* we use a self-signed test server, skip verification during debugging */
curl_easy_setopt(hnd, CURLOPT_SSL_VERIFYPEER, 0L);
curl_easy_setopt(hnd, CURLOPT_SSL_VERIFYHOST, 0L);

/* wait for pipe connection to confirm */
curl_easy_setopt(hnd, CURLOPT_PIPEWAIT, 1L);

/* add the individual transfer */
curl_multi_add_handle(multi_handle, hnd);
curl_multi_setopt(multi_handle, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
/* We do HTTP/2 so let's stick to one connection per host */
curl_multi_setopt(multi_handle, CURLMOPT_MAX_HOST_CONNECTIONS, 1L);
/* we start some action by calling perform right away */
int still_running = 0;
CURLMcode code = curl_multi_perform(multi_handle, &still_running);

struct CURLMsg *m;
do {
int msgq = 0;
m = curl_multi_info_read(multi_handle, &msgq);
if (m && (m->msg == CURLMSG_DONE)) {
CURL *e = m->easy_handle;
curl_multi_remove_handle(multi_handle, e);
curl_easy_cleanup(e);
}
} while (m);
```

The first two lines code showed me that this curl supports http2.
My question is in the while loop, curl_multi_info_read always return NULL, and my callback never get chance to be executed? What have I done ? And how to amend it?
Thanks very much

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Received on 2019-12-19