mongoose web response delay - c++

Question

I am new to mongoose web server. I am developing a simple http server which returning a image in response, everything works fine. But when requesting from browser, irrespect to the file size, it takes exactly 1000 milliseconds to reach the web server event handler.
Is there any configuration to change this delay.
static const char *s_http_port = "8089";
static struct mg_serve_http_opts s_http_serve_opts;
static void send_file(struct mg_connection *nc){
char buf[1024];
int n;
FILE *fp;
const char *file_path = "C:\\sample.jpg";
fp = fopen(file_path, "rb");
if(fp == NULL){
printf("Error, file %s not found.", file_path);
}
char *mimeType = "image/jpg";
fseek(fp, 0L, SEEK_END);
long sz = ftell(fp) + 2;
fseek(fp, 0L, SEEK_SET);
mg_printf(nc,
"HTTP/1.1 200 OK\r\n"
"Cache: no-cache\r\n"
"Content-Type: %s\r\n"
"Content-Length: %d\r\n"
"\r\n",
mimeType,
sz);
while((n = fread(buf, 1, sizeof(buf), fp)) > 0) {
mg_send(nc, buf, n);
}
fclose(fp);
mg_send(nc, "\r\n", 2);
nc->flags |= MG_F_SEND_AND_CLOSE;
}
static void ev_handler(struct mg_connection *nc, int ev, void *ev_data){
struct http_message *hm = (struct http_message *)ev_data;
switch(ev)
{
case MG_EV_HTTP_REQUEST:
{
if(mg_vcmp(&hm->uri, "/hello") == 0){
handle_recv(nc);
} else if(mg_vcmp(&hm->uri, "/img") == 0){
send_file(nc);
} else {
mg_serve_http(nc, (struct http_message *) ev_data, s_http_serve_opts);
}
}
break;
case MG_EV_RECV:
break;
case MG_EV_CLOSE:
break;
}
}
int main(void)
{
struct mg_mgr mgr;
struct mg_connection *nc;
mg_mgr_init(&mgr, NULL);
nc = mg_bind(&mgr, s_http_port, ev_handler);
mg_set_protocol_http_websocket(nc);
s_http_serve_opts.document_root = "./images";
s_http_serve_opts.dav_document_root = "./images";
s_http_serve_opts.enable_directory_listing = "yes";
printf("Starting web server on port %s\n", s_http_port);
for(;;) {
mg_mgr_poll(&mgr, 500);
}
mg_mgr_free(&mgr);
return 0;
}