Invoke a Service

In this section we create a new algorithm, SecondAlg, in which the FirstSvc is invoked.

The header file is,

// file SecondAlg.h
#ifndef SECOND_ALG_H
#define SECOND_ALG_H

#include "SniperKernel/AlgBase.h"

class IfMySvc;

class SecondAlg : public AlgBase
{
    public:
        SecondAlg(const std::string& name);

        bool initialize();
        bool execute();
        bool finalize();

    private:
        unsigned int  m_count;
        IfMySvc*      m_svc;
};
#endif

And the source file is,

// file SecondAlg.cc
#include "SecondAlg.h"
#include "FirstSvc/IfMySvc.h"
#include "SniperKernel/AlgFactory.h"

DECLARE_ALGORITHM(SecondAlg);

SecondAlg::SecondAlg(const std::string& name)
    : AlgBase(name),
      m_count(0)
{
}

bool SecondAlg::initialize()
{
    LogDebug << "in the SecondAlg::initialize()" << std::endl;

    SniperPtr<IfMySvc> _svc(this->getScope(), "MyService");
    if ( _svc.valid() ) {
        LogInfo << "the IfMySvc instance is retrieved" << std::endl;
    }
    else{
        LogError << "Failed to get the IfMySvc instance!" << std::endl;
        return false;
    }
    m_svc = _svc.data();

    return true;
}

bool SecondAlg::execute()
{
    LogDebug << "in the SecondAlg::execute()" << std::endl;

    ++m_count;
    LogInfo << "loop " << m_count << std::endl;

    if ( m_count%2 == 1 ) {
        m_svc->doSomeThing();
    }

    return true;
}

bool SecondAlg::finalize()
{
    LogDebug << "in the SecondAlg::finalize()" << std::endl;
    return true;
}

In order to avoid the retrieval of FirstSvc in each time of the events loop, we retrieve it in initialize(), which is executed only once at the beginning of the application. A class template, SniperPtr, is used for the retrival. Then the raw pointer is assigned to the data member m_svc.

• the template parameter can be the concrete type of the service (FirstSvc), or the pure virtual base class (IfMySvc). We use the later one for flexibility in this example.
• the 1st constructor parameter indicates where to find the service. In most situations it is this->getScope(). It might be different when we have multiple Task instances, which will be described as an advanced topic in later sections.
• the 2nd constructor parameter indicates the name of the service instance;

During the event loop, the service is not always invoked. In this example, it's invoked only when the loop count is odd.