Waitset Use Cases

Using wait-sets and conditions.

Using wait-sets and conditions.

Setting up a wait-set

• Create a wait-set

  DDS_WaitSet* waitset = DDS_WaitSet_new();

• Attach conditions

  DDS_Condition* cond1 = ...;
  DDS_Condition* cond2 = DDS_StatusCondition_as_condition(
                          DDS_Entity_get_statuscondition(entity));
  DDS_Condition* cond3 = DDS_ReadCondition_as_condition(
                          DDS_DataReader_create_readcondition(
                                  reader, 
                                                   DDS_NOT_READ_SAMPLE_STATE,
                                  DDS_ANY_VIEW_STATE,
                                  DDS_ANY_INSTANCE_STATE));
  DDS_Condition* cond4 = DDS_GuardCondition_as_condition(
                          DDS_GuardCondition_new());
  DDS_Condition* cond5 = ...;                                                
  DDS_ReturnCode_t retcode;
   
  retcode = DDS_WaitSet_attach_condition(waitset, cond1);
  if (retcode != DDS_RETCODE_OK) {
      /* ... error */
  }
  retcode = DDS_WaitSet_attach_condition(waitset, cond2);
  if (retcode != DDS_RETCODE_OK) {
      /* ... error */
  }
  retcode = DDS_WaitSet_attach_condition(waitset, cond3);
  if (retcode != DDS_RETCODE_OK) {
      /* ... error */
  }
  retcode = DDS_WaitSet_attach_condition(waitset, cond4);
  if (retcode != DDS_RETCODE_OK) {
      /* ... error */
  }
  retcode = DDS_WaitSet_attach_condition(waitset, cond5);
  if (retcode != DDS_RETCODE_OK) {
      /* ... error */
  }

Waiting for condition(s) to trigger

• Set up a wait-set
• Wait for a condition to trigger or timeout, whichever occurs first

  #define TRUE 1
  #define FALSE 0
  struct DDS_Duration_t timeout = { 0, 1000000 }; /* 1ms */
   
  struct DDS_ConditionSeq active_conditions = DDS_SEQUENCE_INITIALIZER; /* holder for active conditions */
   
  int is_cond1_triggered = FALSE;
  int is_cond2_triggered = FALSE;
  int i;
   
  DDS_ReturnCode_t retcode;
   
  retcode = DDS_WaitSet_wait(waitset, &active_conditions, &timeout);
   
  if (retcode == DDS_RETCODE_TIMEOUT){
   
      /* handle timeout */
   
  } else if (retcode != DDS_RETCODE_OK) {
   
      /* check for other cause of failure */
   
  } else {
      /* success */
      /* check if "cond1" or "cond2" are triggered: */
      for(i = 0; i < DDS_ConditionSeq_get_length(&active_conditions); ++i) {
   
          if (DDS_ConditionSeq_get(&active_conditions, i) == cond1) {
              printf("Cond1 was triggered!");
              is_cond1_triggered = TRUE;
          }
   
          if (DDS_ConditionSeq_get(&active_conditions, i) == cond2) {
              printf("Cond2 was triggered!");
              is_cond2_triggered = TRUE;
          }
          if (is_cond1_triggered && is_cond2_triggered) {
              break;
          }
      }
  }
   
  if (is_cond1_triggered) {
      /* ... do something because "cond1" was triggered ... */
  }
   
  if (is_cond2_triggered) {
      /* ... do something because "cond2" was triggered ... */
  }

Tearing down a wait-set

• Delete the wait-set

  DDS_WaitSet_delete(waitset);
  waitset = NULL;