Xtc Library How-Tos

// %sample:intro:cpp%
// Assume some totally made-up data acquisition callback framework named DAQFramework
// Developers of the psdaq package are welcome to come in and change this toy example
// to match the real DAQ API.

HSDXtcWriter hsdwriter()

DAQFramework.registerHandler("configure", std::bind(hsdwriter.openXtcFile, filename))
DAQFramework.registerHandler("runstart", hsdwriter.setup)
// Assume we get a "readout" message per event
DAQFramework.registerHandler("readout", hsdwriter.writeFeature)
DAQFramework.registerHandler("runend", hsdwriter.closeXtcFile)

//%endsample%

// %sample:codesample1:cpp%

#include "xtcdata/xtc/ShapesData.hh"
#include "xtcdata/xtc/DescData.hh"
#include "xtcdata/xtc/Dgram.hh"
#include "xtcdata/xtc/TypeId.hh"
#include "xtcdata/xtc/XtcIterator.hh"
#include "xtcdata/xtc/VarDef.hh"

// various std library includes omitted...

using namespace XtcData;

#define BUFSIZE 0x4000000

HSDXtcWriter::HSDXtcWriter()
{
	// Define the "signature" of the data in
    // our feature extraction data set
	class FexDef:public VarDef
	{
		public:
		  enum index
		  {
			  floatFex,
		      arrayFex,
		      intFex
	      };

		FexDef()
   		{
       		NameVec.push_back({"floatFex",Name::DOUBLE});
			// "arrayFex" has rank 2; 0 is the default, for scalar data 
			NameVec.push_back({"arrayFex",Name::FLOAT,2});
			NameVec.push_back({"intFex",Name::INT64});
		}
	};


	// Define some instance variables.
	FILE *this->xtcoutfile;
	// -------- Set up the metadata ------------
	// Declare an Xtc::Dgram to store metadata about the output
	Dgram& this->metadataDgram;
	// Declare a NamesVec to store Names info
	NamesVec this->namesVec;
	// Declare a NamesId object to act as composite lookup key
	NamesId this->namesId;
	// Store the node ID of this node
    unsigned this->nodeid = 1;
	// -------- Set up the readout data ---------
	// Declare an Xtc:Dgram to store readout data
	Dgram& this->readoutDgram;
	// Create one of our previously-defined FexDefs
	this->FexDef = new FexDef();

	// Now initialize various things
	_initializeMetadataDgram();
}

void HSDXtcWriter::_initializeMetadataDgram()
{
	TypeId tid(TypeId::Parent, 0);
	void* configbuf = malloc(BUFSIZE);

    this->metadataDgram = *(Dgram*)configbuf;
	this->metadataDgram.xtc.contains = tid;
    this->metadataDgram.xtc.damage = 0;
    this->metadataDgram.xtc.extent = sizeof(Xtc);
}

void HSDXtcWriter::_initializeReadoutDataDgram()
{
	TypeId tid(TypeId::Parent, 0);
	void* buf = malloc(BUFSIZE);

    this->readoutDgram = *(Dgram*)buf;
	this->readoutDgram.xtc.contains = tid;
    this->readoutDgram.xtc.damage = 0;
    this->readoutDgram.xtc.extent = sizeof(Xtc);
}

void HSDXtcWriter::_addNames()
{
	// Instantiate an Alg to define metadata for
    // a feature extraction ("fex") algorithm,
	// version 4.5.6
	Alg hsdFexAlg("fex",4,5,6);
	// Create a NamesId composite lookup key and
	// then a Names structure (ID'd with that key)
 	// that identifies the location, algorithm,
	// detector type and detectorID.
	this->namesId.NamesId(this->nodeId,1); // nodeId=1, namesId = 1
	Names& fexNames = *new(xtc) Names("xpphsd", hsdFexAlg, "hsd", "detnum1234", this->namesId)
	// And now we add the Names structure to the
    // parent Xtc metadata container along with
    // the FexDef data signature.
	fexNames.add(this->metadataDgram.xtc, this->FexDef);
	// add this Names structure to the NamesVec
	this->namesVec[namesId1] = NameIndex(this->fexNames);
}

void HSDXtcWriter::openXtcFile(xtcoutfilename)
{
	this->xtcoutfile = fopen(xtcoutfilename, "w");
}

void HSDXtcWriter::setup()
{
	// Behind this public method, call internal to
	// set up the metadata
	this->_addNames();

	// Omitting code to confirm successful file operation....
	fwrite(&this->metadataDgram, sizeof(this->metadataDgram) + this->metadataDgram.xtc.sizeofPayload(), 1, this->xtcoutfile)

}

void HSDXtcWriter::writeFeature()
{

	// Initialize the Dgram for readout data
	this->initializeReadoutDataDgram();

	// Need some makebelieve code here to show how this
    // callback method unpacks data from DAQ
	// to cram into these Xtc structures...

	// Talk to Chris. Is this event by event? Would you want
    // to destruct this CreateData after each event?
 	CreateData fex(this->readoutDgram.xtc, this->namesVec, this->namesId);

	// Need stub code here to represent getting values from DAQ
	// and using set_value and allocate with something real-ish

	// set_value() lets you set scalar values in the data record.
    // The 'floatFex' ID is defined in our custom FexDef class.
	fex.set_value(FexDef::floatFex, (double)41.0);

	// Use allocate() to set up data that's better represented as
    // vectors or matrices.
    // The 'arrayFex' ID is defined in our custom FexDef class.
	unsigned shape[MaxRank] = {2,3}; //MaxRank is an Xtc library
                                     //global upper limit on data complexity.
    Array<float> arrayT = fex.allocate<float>(this->FexDef::arrayFex, shape);
    for(unsigned i=0; i<shape[0]; i++){
        for (unsigned j=0; j<shape[1]; j++) {
            arrayT(i,j) = 142.0+i*shape[1]+j;
        }
    };
	
	// Another scalar value setter.
    // The 'intFex' ID is defined in our custom FexDef class.
	fex.set_value(FexDef::intFex, (int64_t) 42);

}

void HSDXtcWriter::closeXtcFile()
{
	fclose(this->xtcoutfile);
}

// ...
// %endsample%

// %sample:codesample2:cpp%
	cout<<"Hi world?"
// %endsample%