Waitset Use Cases
[Programming How-To's]

Using wait-sets and conditions. More...

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_OK) {
  
        /* ... check for cause of failure */
  
    } else {
       /* success */
    
       if (DDS_ConditionSeq_get_length(&active_conditions) == 0) {
          /* timeout! */
          printf("Wait timed out!! None of the conditions was triggered.\n");
  
       } else {
          /* 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;