Waitset Use Cases

Using WaitSets and Conditions. More...

Using WaitSets and Conditions.

The following #includes are needed for the examples on this page

#include <iostream>
#include <dds/core/ddscore.hpp>
#include <dds/sub/ddssub.hpp>

Setting up a WaitSet

• Create a WaitSet and attach Conditions

      // Create a WaitSet
      dds::core::cond::WaitSet waitset;
  
      // Create a GuardCondition
      dds::core::cond::GuardCondition guard_cond;
  
      // Create a StatusCondition for a given Entity
      dds::core::cond::StatusCondition status_cond(entity);
  
      // Create a ReadCondition for a reader with a specific DataState
      dds::sub::cond::ReadCondition read_cond(
          reader, dds::sub::status::DataState(
              dds::sub::status::SampleState::not_read(),
              dds::sub::status::ViewState::any(),
              dds::sub::status::InstanceState::any()));
  
      // Attach conditions
      waitset += guard_cond; // using += operator
      waitset += status_cond;
      waitset.attach_condition(read_cond); // or using attach_condition()

Waiting for Condition(s) to trigger

You have two ways to wait for Conditions to trigger: wait or dispatch.

• Wait example

      // Wait for at most 20 seconds until one or more conditions are active and
      // then return them.
      // In case of timeout, active_conditions will be empty.
      dds::core::cond::WaitSet::ConditionSeq active_conditions =
          waitset.wait(dds::core::Duration::from_secs(20));
  
      for (uint32_t i = 0; i < active_conditions.size(); i++) {
          if (active_conditions[i] == guard_cond) {
              std::cout << "guard_cond was triggered\n";
          } else if (active_conditions[i] == status_cond) {
              std::cout << "status_cond was triggered\n";
          } // ...
      }

  
  
• Dispatch example

      using dds::core::cond::Condition;
      using dds::sub::cond::ReadCondition;
  
      // create a WaitSet
      dds::core::cond::WaitSet waitset;
  
      // Create a ReadCondition for reader1 with a functor handler
      ReadCondition read_cond1(reader1, dds::sub::status::DataState::any(), []() {
          std::cout << "read_cond1 was triggered\n";
      });
  
      ReadCondition read_cond2(
              reader2,
              dds::sub::status::DataState::any(),
              [](Condition c) {  // The handler can optionally
                                 // receive the condition
                  auto rc = dds::core::polymorphic_cast<ReadCondition>(c);
                  auto reader = rc.data_reader();  // reader == reader2
                  std::cout << "read_cond2 was triggered (topic is "
                            << reader.topic_name() << ")" << std::endl;
              });
  
      // Attach conditions
      waitset += read_cond1;
      waitset += read_cond2;
  
      // Wait at most 20 seconds until one or more conditions are active and
      // then call the handler of the active conditions. You can repeat this in
      // a loop.
      waitset.dispatch(dds::core::Duration::from_secs(20));

  See also

  Filtering with Query Conditions