Implement AlpakaBackendProducer and AlpakaBackendFilter

Implement AlpakaBackendProducer, an empty alpaka-based EDProducer whose
only purpose is to save in the event what alpaka backend has been used.

Implement AlpakaBackendFilter, an EDFilter that selects events based on
the alpaka backend used to run a previous producer.

Implement a unit test for both modules.

HeterogeneousCore/AlpakaCore/plugins/AlpakaBackendFilter.cc

@@ -0,0 +1,48 @@
+#include <array>
+#include <string>
+#include <vector>
+
+#include "FWCore/Framework/interface/Event.h"
+#include "FWCore/Framework/interface/EventSetup.h"
+#include "FWCore/Framework/interface/global/EDFilter.h"
+#include "FWCore/ParameterSet/interface/ConfigurationDescriptions.h"
+#include "FWCore/ParameterSet/interface/ParameterSet.h"
+#include "FWCore/ParameterSet/interface/ParameterSetDescription.h"
+#include "HeterogeneousCore/AlpakaInterface/interface/Backend.h"
+
+class AlpakaBackendFilter : public edm::global::EDFilter<> {
+public:
+  explicit AlpakaBackendFilter(edm::ParameterSet const& config)
+      : producer_(consumes<unsigned short>(config.getParameter<edm::InputTag>("producer"))), backends_{} {
+    for (auto const& backend : config.getParameter<std::vector<std::string>>("backends")) {
+      backends_[static_cast<unsigned short>(cms::alpakatools::toBackend(backend))] = true;
+    }
+  }
+
+  bool filter(edm::StreamID sid, edm::Event& event, edm::EventSetup const& setup) const final {
+    return backends_[event.get(producer_)];
+  }
+
+  static void fillDescriptions(edm::ConfigurationDescriptions& descriptions);
+
+private:
+  const edm::EDGetTokenT<unsigned short> producer_;
+  std::array<bool, static_cast<short>(cms::alpakatools::Backend::size)> backends_;
+};
+
+void AlpakaBackendFilter::fillDescriptions(edm::ConfigurationDescriptions& descriptions) {
+  edm::ParameterSetDescription desc;
+  desc.add<edm::InputTag>("producer", edm::InputTag("alpakaBackendProducer", "backend"))
+      ->setComment(
+          "Use the 'backend' instance label to read the backend indicator that is implicitly produced by every alpaka "
+          "EDProducer.");
+  desc.add<std::vector<std::string>>("backends", {"SerialSync"})
+      ->setComment("Valid backends are 'SerialSync', 'CudaAsync', 'ROCmAsync', and 'TbbAsync'.");
+  descriptions.addWithDefaultLabel(desc);
+  descriptions.setComment(
+      "This EDFilter accepts events if the alpaka EDProducer 'producer' was run on a backend among those listed by the "
+      "'backends' parameter.");
+}
+
+#include "FWCore/Framework/interface/MakerMacros.h"
+DEFINE_FWK_MODULE(AlpakaBackendFilter);

HeterogeneousCore/AlpakaCore/plugins/BuildFile.xml

@@ -3,5 +3,17 @@
   <use name="FWCore/MessageLogger"/>
   <use name="FWCore/ParameterSet"/>
   <use name="FWCore/Utilities"/>
+  <use name="HeterogeneousCore/AlpakaInterface"/>
+  <flags EDM_PLUGIN="1"/>
+</library>
+
+<library file="alpaka/*.cc" name="HeterogeneousCoreAlpakaTestPluginsPortable">
+  <use name="alpaka"/>
+  <use name="FWCore/Framework"/>
+  <use name="FWCore/ParameterSet"/>
+  <use name="FWCore/Utilities"/>
+  <use name="HeterogeneousCore/AlpakaCore"/>
+  <use name="HeterogeneousCore/AlpakaInterface"/>
+  <flags ALPAKA_BACKENDS="1"/>
   <flags EDM_PLUGIN="1"/>
 </library>

HeterogeneousCore/AlpakaCore/plugins/alpaka/AlpakaBackendProducer.cc

@@ -0,0 +1,31 @@
+#include "FWCore/Framework/interface/Frameworkfwd.h"
+#include "FWCore/ParameterSet/interface/ConfigurationDescriptions.h"
+#include "FWCore/ParameterSet/interface/ParameterSet.h"
+#include "FWCore/ParameterSet/interface/ParameterSetDescription.h"
+#include "FWCore/Utilities/interface/StreamID.h"
+#include "HeterogeneousCore/AlpakaCore/interface/alpaka/Event.h"
+#include "HeterogeneousCore/AlpakaCore/interface/alpaka/EventSetup.h"
+#include "HeterogeneousCore/AlpakaCore/interface/alpaka/global/EDProducer.h"
+#include "HeterogeneousCore/AlpakaInterface/interface/config.h"
+
+namespace ALPAKA_ACCELERATOR_NAMESPACE {
+
+  class AlpakaBackendProducer : public global::EDProducer<> {
+  public:
+    AlpakaBackendProducer(edm::ParameterSet const& config){};
+
+    void produce(edm::StreamID sid, device::Event& event, device::EventSetup const&) const override {}
+
+    static void fillDescriptions(edm::ConfigurationDescriptions& descriptions) {
+      edm::ParameterSetDescription desc;
+      descriptions.addWithDefaultLabel(desc);
+      descriptions.setComment(
+          "The alpaka EDProducer does not have any explicit products. "
+          "Its only purpose is to produce a 'backend' value.");
+    }
+  };
+
+}  // namespace ALPAKA_ACCELERATOR_NAMESPACE
+
+#include "HeterogeneousCore/AlpakaCore/interface/alpaka/MakerMacros.h"
+DEFINE_FWK_ALPAKA_MODULE(AlpakaBackendProducer);

HeterogeneousCore/AlpakaCore/test/BuildFile.xml

@@ -0,0 +1,3 @@
+<test name="testAlpakaBackendFilter" command="cmsRun ${LOCALTOP}/src/HeterogeneousCore/AlpakaCore/test/testAlpakaBackendFilter.py">
+  <flags ALPAKA_BACKENDS="1"/>
+</test>

HeterogeneousCore/AlpakaCore/test/testAlpakaBackendFilter.py

@@ -0,0 +1,41 @@
+import os
+import sys
+
+# choose a different alpaka backend depending on the SCRAM test being run
+try:
+    backend = os.environ['SCRAM_TEST_NAME'].replace('testAlpakaBackendFilter', '')
+except:
+    backend = 'SerialSync'
+
+# map the alpaka backends to the process accelerators
+accelerators = {
+    'SerialSync': 'cpu',
+    'CudaAsync':  'gpu-nvidia',
+    'ROCmAsync':  'gpu-amd'
+}
+
+import FWCore.ParameterSet.Config as cms
+from HeterogeneousCore.AlpakaCore.functions import *
+
+process = cms.Process('Test')
+
+process.options.accelerators = [ accelerators[backend] ]
+
+process.maxEvents.input = 10
+
+process.source = cms.Source('EmptySource')
+
+process.load('Configuration.StandardSequences.Accelerators_cff')
+process.load('HeterogeneousCore.AlpakaCore.ProcessAcceleratorAlpaka_cfi')
+
+process.alpakaBackendProducer = cms.EDProducer('AlpakaBackendProducer@alpaka')
+
+process.alpakaBackendFilter = cms.EDFilter('AlpakaBackendFilter',
+  producer = cms.InputTag('alpakaBackendProducer', 'backend'),
+  backends = cms.vstring(backend)
+)
+
+process.SelectedBackend = cms.Path(process.alpakaBackendProducer + process.alpakaBackendFilter)
+process.AnyOtherBackend = cms.Path(process.alpakaBackendProducer + ~process.alpakaBackendFilter)
+
+process.options.wantSummary = True