Is it possible to read a data before write to queue?

Hi, I'm just trying to read or take a data  before write to queue.

static void on_data_available_callback(void *listener_data /* unused */, 
 DDS_DataReader* data_reader) {
 DDS_StringDataReader *string_reader = NULL;
 char sample[MAX_STRING_SIZE]; 
 struct DDS_SampleInfo info;
 DDS_ReturnCode_t retcode;
 int i=0;

string_reader = DDS_StringDataReader_narrow(data_reader);

 if (string_reader == NULL) {
 /* In this specific case, this will never fail */
 puts("DDS_StringDataReader_narrow failed.");
 return;
 }
 
 Sleep(1000);
 /* Loop until there are messages available in the queue */
 for(;;) {
 retcode = DDS_StringDataReader_read_next_sample(
 string_reader,
 sample,
 &info);
 
 if (retcode == DDS_RETCODE_NO_DATA) {
 /* No more samples */
 printf("Read a data : \n");
 printf("Empty Queue\n");
 Sleep(1000);
 //break;
 } else if (retcode != DDS_RETCODE_OK) {
 printf("Unable to take data from data reader, error %d\n", retcode);
 return;
 }

if(retcode != DDS_RETCODE_NO_DATA) {
 if (info.valid_data) {
 /* Data is valid (this isn't just a lifecycle sample): print it */
 printf("Read a data : \n");
 puts(sample);
 /* If empty string is received, clean shutdown*/
 if(strlen(sample) == 0){
 shutdown_flag = DDS_BOOLEAN_TRUE; 
 }
 }
 Sleep(2000);
 }
 }

I tried to start my publisher and my subscriber simultaneously. But, everytime, subscriber read a data when publisher write a data to queue only.

Is it possible to read a data before write? If then, what can I do?

Thanks

 Hyunji