DDS Listener & waitset

Something worth pointing out is that the handler code will execute in a middleware thread.

As a result, when using listeners you should try to minimize the time spent in the listener itself.

DDS有兩種async模式，listener和waitset  (這邊指的async是main thread不用一直去poll dds_read)

listener 有點像一般的callback，程式碼也較簡單

而waitset則是讓main thread等一段時間，等到事件觸發再去做事情

程式碼較多

但是，listener 裡面如果程式執行太久會影響底層的DDS接收data  (會掉資料，嚴重的話程式會死掉)

所以當你程式較複雜的話，建議用waitset 搭配thread去做處理

listener比較適合簡單的使用情境

listener :

static void data_available_handler (dds_entity_t reader) {     /*read or take data*/     dds_take (reader, samples, max_samples, info, mask); }     void main(void) {     dds_readerlistener_t listener = {0};     listener.on_data_available = data_available_handler;         dds_reader_create (subscriber, &reader, topic, qos, &listener);         /* wait listener*/     while(1) {         dds_sleepfor(DDS_MSECS(100));     } }

waitset :

void main(void) {     dds_reader_create (subscriber, &reader, topic, qos, NULL);         dds_waitset_t ws = dds_waitset_create ();     dds_condition_t cond = dds_readcondition_create(reader,mask);     dds_waitset_attach(ws,cond,reader);           dds_attach_t wsresults[1];     size_t wsresultsize = 1u;     dds_time_t timeout = DDS_SECS (10);         while(1) {         ret = dds_waitset_wait (ws, wsresults, wsresultsize, timeout);         if (ret > 0) {             dds_take (wsresults, samples, max_samples, info, mask);         }         dds_sleepfor(DDS_MSECS(100));     } }