gdetector_example.cc

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// gdetector
#include "gdetectorConstruction.h"
#include "gdetector_options.h"
 
// gemc
#include "glogger.h"
#include "event/gEventDataCollection.h"
#include "gdynamicdigitizationConventions.h"
#include "gthreads.h"
 
// geant4
#include "G4RunManagerFactory.hh"
#include "QBBC.hh"
 
// c++
#include <atomic>         // std::atomic<T>: lock-free, thread-safe integers, flags…
#include <vector>
#include <memory>         // smart pointers
 

auto run_simulation_in_threads(int                                                 nevents,
                               int                                                 nthreads,
                               const std::shared_ptr<GOptions>&                    gopts,
                               const std::shared_ptr<GLogger>&                     log,
                               const GDetectorConstruction*                         gdetector) -> std::vector<std::shared_ptr<GEventDataCollection>> {
    std::mutex                                         collectorMtx;
    std::vector<std::shared_ptr<GEventDataCollection>> collected;
 
    // thread-safe integer counter starts at 1.
    // fetch_add returns the old value *and* bumps.
    // zero contention: each thread fetches the next free event number.
    std::atomic<int> next{1};
 
    // pool of jthreads.  jthread joins in its destructor so we don’t need an
    // explicit loop at the end.
    // each element represents one worker thread running your event-processing lambda.
    // std::vector<std::jthread> pool; use this when C++20 is widely available
    std::vector<jthread_alias> pool; // was std::vector<std::jthread>
 
    pool.reserve(nthreads);
 
    for (int tid = 0; tid < nthreads; ++tid) {
        // The capture [&, tid] gives the thread references to variables like tid
        pool.emplace_back([&, tid] // capture tid *by value*
        {
            log->info(0, "worker %1 started", tid);
 
            int localCount = 0; // events built by *this* worker
 
            // Per-thread staging buffer (thread_local) used before final collection.
            // The collection step below uses a mutex to merge results into "collected".
            thread_local std::vector<std::shared_ptr<GEventDataCollection>> localRunData;
 
            while (true) {
                // repeatedly asks the shared atomic counter for “the next unclaimed event
                // number,” processes that event, stores the result, and goes back for more.
                // memory_order_relaxed: we only need *atomicity*, no ordering
                int evn = next.fetch_add(1, std::memory_order_relaxed); // atomically returns the current value and increments it by 1.
                if (evn > nevents) break;                               // exit the while loop
 
                // flux does not need variation or run number
                std::string sdname    = "flux";
                int         runNumber = 1;
                std::string variation = "default";
 
                auto gevent_header      = GEventHeader::create(gopts, tid);
                auto eventData    = std::make_shared<GEventDataCollection>(gopts, std::move(gevent_header));
                auto digi_routine = gdetector->get_digitization_routines_for_sdname(sdname);
                log->debug(NORMAL, "Calling %1 loadConstants for run %2", sdname, runNumber);
 
                if (digi_routine->loadConstants(runNumber, variation) == false) {
                    log->error(
                        ERR_LOADCONSTANTFAIL, "Failed to load constants for %1 for run %2 with variation %3",
                        sdname, runNumber, variation);
                }
 
                log->debug(NORMAL, "Calling %1 loadTT for run %2", sdname, runNumber);
                if (digi_routine->loadTT(runNumber, variation) == false) {
                    log->error(
                        ERR_LOADTTFAIL, "Failed to load translation table for %1 for run %2 with variation %3",
                        sdname, runNumber, variation);
                }
                // each event has 10 hits
                for (unsigned i = 1; i < 11; i++) {
                    auto hit       = GHit::create(gopts);
                    auto true_data = digi_routine->collectTrueInformation(hit, i);
                    auto digi_data = digi_routine->digitizeHit(hit, i);
 
                    eventData->addDetectorDigitizedData("flux", std::move(digi_data));
                    eventData->addDetectorTrueInfoData("flux", std::move(true_data));
                }
 
                const auto& flux_data_it = eventData->getDataCollectionMap().find("flux");
 
 
                if (flux_data_it != eventData->getDataCollectionMap().end()) {
                    const auto& digitized_data = flux_data_it->second->getDigitizedData();
                    log->info(0, "worker %1 event %2 has %3 digitized hits", tid, evn, digitized_data.size());
                }
 
                // NOTE: This example does not currently push eventData into localRunData.
                // localRunData is retained to demonstrate a typical staging/merge pattern
                // used in multi-threaded pipelines.
                ++localCount; // tally for this worker
            }
 
            // braces to locks the mutex when it's constructed and unlocks when it is destroyed
            {
                std::scoped_lock lk(collectorMtx);
                for (auto& evt : localRunData) { collected.emplace_back(evt); }
                localRunData.clear();
            }
 
 
            log->info(0, "worker %1 processed %2 events", tid, localCount);
        }); // jthread constructor launches the thread immediately
    }       // pool’s destructor blocks until every jthread has joined
    return collected;
}
 

int main(int argc, char* argv[]) {
    // Create GOptions using gdata::defineOptions, which aggregates options from gdata and gtouchable.
    auto gopts = std::make_shared<GOptions>(argc, argv, gdetector::defineOptions());
 
    // Create loggers: one for gdata and one for gtouchable.
    auto log = std::make_shared<GLogger>(gopts, SFUNCTION_NAME, GDETECTOR_LOGGER);
 
    constexpr int nevents  = 20;
    constexpr int nthreads = 2;
 
    auto runManager  = G4RunManagerFactory::CreateRunManager(G4RunManagerType::Default);
    auto physicsList = new QBBC;
 
    runManager->SetUserInitialization(physicsList);
 
    auto gdetector = new GDetectorConstruction(gopts);
    runManager->SetUserInitialization(gdetector);
 
    auto gsystems = gsystem::getSystems(gopts);
    gdetector->reload_geometry(gsystems);
 
    auto runDat = run_simulation_in_threads(nevents, nthreads, gopts, log, gdetector);
 
    return EXIT_SUCCESS;
}