[RF] Avoid compute graph desync in RooFixedProdPdf

The RooFixedProdPdf used an antipattern that should be avoided, and it
was actually causing some problems in fits with the new CPU evaluation
backend.

The problem was that the class held on to some RooAbsArgs for its
evaluation in some containers that were separate from RooFit
server-client interface (the container was the
`std::unique_ptr<RooProdPdf::CacheElem>`).

This commit fixes the situation by avoiding this cache element member
completely and consistently using the server proxies instead.

Author: guitargeek

roofit/codegen/src/CodegenImpl.cxx

@@ -137,10 +137,10 @@ std::string realSumPdfTranslateImpl(CodegenContext &ctx, RooAbsArg const &arg, R
 
 void codegenImpl(RooFit::Detail::RooFixedProdPdf &arg, CodegenContext &ctx)
 {
-   if (arg.cache()._isRearranged) {
-      ctx.addResult(&arg, ctx.buildCall(mathFunc("ratio"), *arg.cache()._rearrangedNum, *arg.cache()._rearrangedDen));
+   if (arg.isRearranged()) {
+      ctx.addResult(&arg, ctx.buildCall(mathFunc("ratio"), *arg.rearrangedNum(), *arg.rearrangedDen()));
    } else {
-      ctx.addResult(&arg, ctx.buildCall(mathFunc("product"), arg.cache()._partList, arg.cache()._partList.size()));
+      ctx.addResult(&arg, ctx.buildCall(mathFunc("product"), *arg.partList(), arg.partList()->size()));
    }
 }
 

roofit/roofitcore/inc/RooProdPdf.h

@@ -178,7 +178,6 @@ class RooProdPdf : public RooAbsPdf {
   std::unique_ptr<RooAbsReal> specializeIntegral(RooAbsReal& orig, const char* targetRangeName) const ;
   std::unique_ptr<RooAbsReal> specializeRatio(RooFormulaVar& input, const char* targetRangeName) const ;
   double calculate(const RooProdPdf::CacheElem& cache, bool verbose=false) const ;
-  void doEvalImpl(RooAbsArg const* caller, const RooProdPdf::CacheElem &cache, RooFit::EvalContext &) const;
 
 
   friend class RooProdGenContext ;
@@ -202,15 +201,10 @@ class RooProdPdf : public RooAbsPdf {
   bool _selfNorm = true; ///< Is self-normalized
   RooArgSet _defNormSet ; ///< Default normalization set
 
-private:
-
-
-
   ClassDefOverride(RooProdPdf,6) // PDF representing a product of PDFs
 };
 
-namespace RooFit {
-namespace Detail {
+namespace RooFit::Detail {
 
 /// A RooProdPdf with a fixed normalization set can be replaced by this class.
 /// Its purpose is to provide the right client-server interface for the
@@ -227,7 +221,7 @@ class RooFixedProdPdf : public RooAbsPdf {
 
    inline bool canComputeBatchWithCuda() const override { return true; }
 
-   inline void doEval(RooFit::EvalContext &ctx) const override { _prodPdf->doEvalImpl(this, *_cache, ctx); }
+   void doEval(RooFit::EvalContext &ctx) const override;
 
    inline ExtendMode extendMode() const override { return _prodPdf->extendMode(); }
    inline double expectedEvents(const RooArgSet * /*nset*/) const override
@@ -260,22 +254,30 @@ class RooFixedProdPdf : public RooAbsPdf {
       return _prodPdf->analyticalIntegral(code, rangeName);
    }
 
-   RooProdPdf::CacheElem const &cache() const { return *_cache; }
+   bool isRearranged() const { return _isRearranged; }
 
-private:
-   void initialize();
+   RooAbsReal const *rearrangedNum() const
+   {
+      return _isRearranged ? static_cast<RooAbsReal const *>(_servers[0]) : nullptr;
+   }
+   RooAbsReal const *rearrangedDen() const
+   {
+      return _isRearranged ? static_cast<RooAbsReal const *>(_servers[1]) : nullptr;
+   }
+
+   RooArgSet const *partList() const { return !_isRearranged ? static_cast<RooArgSet const *>(&_servers) : nullptr; }
 
-   inline double evaluate() const override { return _prodPdf->calculate(*_cache); }
+private:
+   double evaluate() const override;
 
    RooArgSet _normSet;
-   std::unique_ptr<RooProdPdf::CacheElem> _cache;
    RooSetProxy _servers;
    std::unique_ptr<RooProdPdf> _prodPdf;
+   bool _isRearranged = false;
 
    ClassDefOverride(RooFit::Detail::RooFixedProdPdf, 0);
 };
 
-} // namespace Detail
-} // namespace RooFit
+} // namespace RooFit::Detail
 
 #endif

roofit/roofitcore/src/RooProdPdf.cxx

@@ -409,26 +409,6 @@ double RooProdPdf::calculate(const RooProdPdf::CacheElem& cache, bool /*verbose*
   }
 }
 
-////////////////////////////////////////////////////////////////////////////////
-/// Evaluate product of PDFs in batch mode.
-void RooProdPdf::doEvalImpl(RooAbsArg const *caller, const RooProdPdf::CacheElem &cache, RooFit::EvalContext &ctx) const
-{
-   if (cache._isRearranged) {
-      auto numerator = ctx.at(cache._rearrangedNum.get());
-      auto denominator = ctx.at(cache._rearrangedDen.get());
-      RooBatchCompute::compute(ctx.config(caller), RooBatchCompute::Ratio, ctx.output(), {numerator, denominator});
-   } else {
-      std::vector<std::span<const double>> factors;
-      factors.reserve(cache._partList.size());
-      for (const RooAbsArg *i : cache._partList) {
-         auto span = ctx.at(i);
-         factors.push_back(span);
-      }
-      std::array<double, 1> special{static_cast<double>(factors.size())};
-      RooBatchCompute::compute(ctx.config(caller), RooBatchCompute::ProdPdf, ctx.output(), factors, special);
-   }
-}
-
 namespace {
 
 template<class T>
@@ -2185,44 +2165,85 @@ RooProdPdf::compileForNormSet(RooArgSet const &normSet, RooFit::Detail::CompileC
    return fixedProdPdf;
 }
 
-namespace RooFit {
-namespace Detail {
+namespace RooFit::Detail {
 
 RooFixedProdPdf::RooFixedProdPdf(std::unique_ptr<RooProdPdf> &&prodPdf, RooArgSet const &normSet)
    : RooAbsPdf(prodPdf->GetName(), prodPdf->GetTitle()),
      _normSet{normSet},
      _servers("!servers", "List of servers", this),
      _prodPdf{std::move(prodPdf)}
 {
-   initialize();
+   auto cache = _prodPdf->createCacheElem(&_normSet, nullptr);
+   _isRearranged = cache->_isRearranged;
+
+   // The actual servers for a given normalization set depend on whether the
+   // cache is rearranged or not. See RooProdPdf::calculate to see
+   // which args in the cache are used directly.
+   if (_isRearranged) {
+      _servers.add(*cache->_rearrangedNum);
+      _servers.add(*cache->_rearrangedDen);
+      addOwnedComponents(std::move(cache->_rearrangedNum));
+      addOwnedComponents(std::move(cache->_rearrangedDen));
+      return;
+   }
+   // We don't want to carry the full cache object around, so we let it go out
+   // of scope and transfer the ownership of the args that we actually need.
+   cache->_ownedList.releaseOwnership();
+   std::vector<std::unique_ptr<RooAbsArg>> owned;
+   for (RooAbsArg *arg : cache->_ownedList) {
+      owned.emplace_back(arg);
+   }
+   for (RooAbsArg *arg : cache->_partList) {
+      _servers.add(*arg);
+      auto found = std::find_if(owned.begin(), owned.end(), [&](auto const &ptr) { return arg == ptr.get(); });
+      if (found != owned.end()) {
+         addOwnedComponents(std::move(owned[std::distance(owned.begin(), found)]));
+      }
+   }
 }
 
 RooFixedProdPdf::RooFixedProdPdf(const RooFixedProdPdf &other, const char *name)
    : RooAbsPdf(other, name),
      _normSet{other._normSet},
-     _servers("!servers", "List of servers", this),
-     _prodPdf{static_cast<RooProdPdf *>(other._prodPdf->Clone())}
+     //_servers("!servers", "List of servers", this),
+     _servers("!servers", this, other._servers),
+     _prodPdf{static_cast<RooProdPdf *>(other._prodPdf->Clone())},
+     _isRearranged{other._isRearranged}
+{
+}
+
+////////////////////////////////////////////////////////////////////////////////
+/// Evaluate product of PDFs in batch mode.
+
+void RooFixedProdPdf::doEval(RooFit::EvalContext &ctx) const
 {
-   initialize();
+   if (_isRearranged) {
+      auto numerator = ctx.at(rearrangedNum());
+      auto denominator = ctx.at(rearrangedDen());
+      RooBatchCompute::compute(ctx.config(this), RooBatchCompute::Ratio, ctx.output(), {numerator, denominator});
+      return;
+   }
+   std::vector<std::span<const double>> factors;
+   factors.reserve(partList()->size());
+   for (const RooAbsArg *arg : *partList()) {
+      auto span = ctx.at(arg);
+      factors.push_back(span);
+   }
+   std::array<double, 1> special{static_cast<double>(factors.size())};
+   RooBatchCompute::compute(ctx.config(this), RooBatchCompute::ProdPdf, ctx.output(), factors, special);
 }
 
-void RooFixedProdPdf::initialize()
+double RooFixedProdPdf::evaluate() const
 {
-   _cache = _prodPdf->createCacheElem(&_normSet, nullptr);
-   auto &cache = *_cache;
+   if (_isRearranged) {
+      return rearrangedNum()->getVal() / rearrangedDen()->getVal();
+   }
+   double value = 1.0;
 
-   // The actual servers for a given normalization set depend on whether the
-   // cache is rearranged or not. See RooProdPdf::calculateBatch to see
-   // which args in the cache are used directly.
-   if (cache._isRearranged) {
-      _servers.add(*cache._rearrangedNum);
-      _servers.add(*cache._rearrangedDen);
-   } else {
-      for (std::size_t i = 0; i < cache._partList.size(); ++i) {
-         _servers.add(cache._partList[i]);
-      }
+   for (auto *arg : static_range_cast<RooAbsReal *>(*partList())) {
+      value *= arg->getVal();
    }
+   return value;
 }
 
-} // namespace Detail
-} // namespace RooFit
+} // namespace RooFit::Detail