The O2Device is meant to build O2 specific behaviours on top of plain FairMQDevices.

The header O2Device/Utilities.h contains utilities that enable consistent handling of data in the O2 format and some useful definitions.

O2Message - currently alias of FairMQPArts, contains FairMQMessages in header-payload order

Allows to consistently create O2 compatible messages for FairMQ transport. Appends a header::Stack-data pair to message. Sets the data size in the DataHeader inside the stack based either on the message/container size.

template <typename T>
addDataBlock(O2Message& message, o2::header::Stack&& headerStack, T data);

• headerStack: as the name implies.

• data:

  • FairMQMessagePtr (std::unique_ptr<FairMQMessage>)
  • STL-like container that uses a pmr::polymorphic_allocator as allocator. Note: this is only efficient if the memory resource used to construct the allocator is o2::pmr::ChannelResource, otherwise an implicit copy occurs.

Executes a function on each data block within the message.

template<typename T>
T forEach(O2Message& message, T function);

the function is a callable object (lambda, functor, std::function) and needs to take two arguents of type gsl::span, first one points to the header buffer, second one points to the payload buffer, e.g. [](span header, span payload) {}.

// make sure we have the allocator associated with the transport appropriate for the selected channel:
auto outputChannelAllocator = o2::pmr::getTransportAllocator(GetChannel("dataOut").Transport());

//the data
using namespace boost::container::pmr;
o2::pmr::vector<int> dataVector(outputChannelAllocator);
dataVector.reserve(10);
dataVector.push_back(1);
dataVector.push_back(2);

//create the message
O2message message;
addDataBlock(message,
             o2::header::Stack{outputChannelAllocator, DataHeader{<args>}},
             std::move(dataVector));

addDataBlock(message,
             o2::header::Stack{outputChannelAllocator, DataHeader{<args>}},
             NewMessageFor("dataOut",0,"some message string"));

Send(message,"dataOut");

//On the receiving end:
O2Message messageIn;
Receive(messageIn, "dataIn");
forEach(messageIn, [](span header, span payload) {
  auto dataHeader = get<DataHeader*>(header.data());
  if (dataHeader->dataDescription==gDataDescriptionMyDataType) {
    MyDataType* myData = reinterpret_cast<MyDataType*>(payload.data());
  }
});