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DPL: give each stream its own slot in the service registry #15680

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DPL: give each stream its own slot in the service registry #15680

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13 changes: 12 additions & 1 deletion Framework/Core/include/Framework/ServiceRegistry.h
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Original file line number Diff line number Diff line change
Expand Up @@ -177,7 +177,18 @@ struct ServiceRegistry {

constexpr InstanceId instanceFromTypeSalt(ServiceTypeHash type, Salt salt) const
{
return InstanceId{type.hash ^ valueFromSalt(salt)};
// Fold the whole salt down into the low bits. The slot is the low bits of
// this (see indexFromInstance) while streamId sits at bit 16 of
// valueFromSalt, so using that directly gives every stream the same slot
// for a given service: they pile into one probe window, and once it is
// MAX_DISTANCE deep the next registration is refused -- reported against
// whichever service happened to lose, not the one which filled it.
//
// Widening the table does not help on its own: the mask stays below bit 16
// until MAX_SERVICES passes 65536.
uint32_t mixed = static_cast<uint32_t>(static_cast<uint16_t>(salt.streamId)) * 0x9E3779B9u ^
static_cast<uint32_t>(static_cast<uint16_t>(salt.dataProcessorId));
return InstanceId{type.hash ^ mixed};
}

constexpr Index indexFromInstance(InstanceId id) const
Expand Down
45 changes: 45 additions & 0 deletions Framework/Core/test/test_Services.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
#include <catch_amalgamated.hpp>
#include <fairmq/ProgOptions.h>
#include <memory>
#include <vector>

TEST_CASE("TestServiceRegistry")
{
Expand Down Expand Up @@ -213,6 +214,50 @@ TEST_CASE("TestStreamServices")
REQUIRE_THROWS_AS(registry.get({TypeIdHelpers::uniqueId<DummyService>()}, salt_1_1, ServiceKind::Stream), RuntimeErrorRef);
}

TEST_CASE("TestStreamServicesDoNotShareASlot")
{
using namespace o2::framework;
ServiceRegistry registry;

ServiceSpec spec{.name = "dummy-service",
.uniqueId = CommonServices::simpleServiceId<DummyService>(),
.init = CommonServices::simpleServiceInit<DummyService, DummyService>(),
.configure = CommonServices::noConfiguration(),
.kind = ServiceKind::Stream};

DeviceState state;
fair::mq::ProgOptions options;
registry.declareService(spec, state, options, ServiceRegistry::globalDeviceSalt());

// One instance of the same service per stream, and more streams than a probe
// window is deep. The slot comes from the low bits of the type hash combined
// with the salt, so if the salt's streamId does not reach those bits every one
// of these lands on the same slot, and the first which does not fit in the
// window is refused outright.
constexpr short STREAMS = 32;
std::vector<DummyService> services(STREAMS);
for (short i = 0; i < STREAMS; ++i) {
services[i].threadId = i + 1;
}

for (short i = 0; i < STREAMS; ++i) {
// Refused registration is what a shared slot looks like from here: the
// window fills and the next one has nowhere to go.
REQUIRE_NOTHROW(registry.registerService({TypeIdHelpers::uniqueId<DummyService>()}, &services[i], ServiceKind::Stream,
ServiceRegistry::Salt{static_cast<short>(i + 1), 0}, "dummy-service",
ServiceRegistry::SpecIndex{0}));
}

// Every stream must get its own instance back, not a neighbour's.
for (short i = 0; i < STREAMS; ++i) {
auto* found = reinterpret_cast<DummyService*>(
registry.get({TypeIdHelpers::uniqueId<DummyService>()},
ServiceRegistry::Salt{static_cast<short>(i + 1), 0}, ServiceKind::Stream));
REQUIRE(found != nullptr);
CHECK(found->threadId == i + 1);
}
}

TEST_CASE("TestServiceRegistryCtor")
{
using namespace o2::framework;
Expand Down