Waitset Use Cases
[Programming How-To's]

Using wait-sets and conditions. More...

Setting up a wait-set

• Create a wait-set

    DDSWaitSet* waitset = new DDSWaitSet();
  

• Attach conditions

    DDSCondition* cond1 = ...;
    DDSCondition* cond2 = entity->get_statuscondition();
    DDSCondition* cond3 = reader->create_readcondition(DDS_NOT_READ_SAMPLE_STATE,
                                                       DDS_ANY_VIEW_STATE,
                                                       DDS_ANY_INSTANCE_STATE);
    DDSCondition* cond4 = new DDSGuardCondition();
    DDSCondition* cond5 = ...;
    DDS_ReturnCode_t retcode;
  
    retcode = waitset->attach_condition(cond1);
    if (retcode != DDS_RETCODE_OK) {
        // ... error
    }
    retcode = waitset->attach_condition(cond2);
    if (retcode != DDS_RETCODE_OK) {
        // ... error
    }
    retcode = waitset->attach_condition(cond3);
    if (retcode != DDS_RETCODE_OK) {
        // ... error
    }
    retcode = waitset->attach_condition(cond4);
    if (retcode != DDS_RETCODE_OK) {
        // ... error
    }
    retcode = waitset->attach_condition(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

    DDS_Duration_t timeout = { 0, 1000000 }; // 1ms
  
    DDSConditionSeq active_conditions; // holder for active conditions
  
    bool is_cond1_triggered = false;
    bool is_cond2_triggered = false;
  
    DDS_ReturnCode_t retcode;
  
    retcode = waitset->wait(active_conditions, timeout);
  
    if (retcode != DDS_RETCODE_OK) {
  
        // ... check for cause of failure
  
    } else {
       // success
    
       if (active_conditions.length() == 0) {
          // timeout!
          printf("Wait timed out!! None of the conditions was triggered.\n");
  
       } else {
          // check if "cond1" or "cond2" are triggered:
          for(int i = 0; i < active_conditions.length(); ++i) {
  
             if (active_conditions[i] == cond1) {
                printf("Cond1 was triggered!");
                is_cond1_triggered = true;              
             }
  
             if (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

    delete waitset;
    waitset = NULL;