root-project · guitargeek · Sep 12, 2026 · Sep 10, 2026 · Sep 9, 2026
@@ -2,7 +2,6 @@ CMAKE_CXX_STANDARD=23
 builtin_civetweb=ON
 experimental_adaptivecpp=OFF
 pythia8=ON
-roofit_multiprocess=ON
 test_distrdf_dask=OFF
 test_distrdf_pyspark=OFF
 vdt=OFF
@@ -1,7 +1,6 @@
 CMAKE_CXX_STANDARD=23
 experimental_adaptivecpp=OFF
 pythia8=ON
-roofit_multiprocess=ON
 test_distrdf_pyspark=OFF
 vdt=OFF
 cefweb=ON
@@ -67,7 +67,6 @@ pyroot=ON
 pythia8=OFF
 qt6web=OFF
 roofit=ON
-roofit_multiprocess=OFF
 root7=ON
 rootbench=OFF
 roottest=ON

@@ -3,4 +3,3 @@ pythia8=ON
 test_distrdf_dask=OFF
 test_distrdf_pyspark=OFF
 vdt=OFF
-roofit_multiprocess=ON
@@ -50,6 +50,7 @@ The following people have contributed to this new version:
 * The overloads of `RooAbsReal::createChi2()` and `RooAbsReal::chi2FitTo()` that take unbinned **RooDataSet** data objects were deprecated in ROOT 6.40 and are now removed.
 * The **RooStats::HybridPlot** class and the related **HybridResult::GetPlot** method were deprecated in ROOT 6.40 and are now removed.
 * The `builtin_zeromq` and `builtin_cppzmq` build options that were deprecated in ROOT 6.40 are now removed.
+* The `roofit_multiprocess` build option is deprecated and will be removed in ROOT 6.44. It has no effect anymore: RooFit's multi-process test statistics no longer depend on ZeroMQ and are now always built on non-Windows platforms, so there is no reason for an opt-in build option anymore (see the RooFit section below).
 * The ROOT **auth** package together with `TVirtualAuth` and `TROOT::GetListOfSecContexts()`, and the **authenticated sockets** (`TSocket::CreateAuthSocket()`) feature are now removed following deprecation in ROOT 6.40.
 * The `TSSLSocket` class is now removed following deprecation in ROOT 6.40.
 * The bindings to the R programming language that are enabled with the `r=ON` or `tmva-rmva=ON` build options (`TRInterface`, RMVA, and friends) are removed, following deprecation in ROOT 6.40. Their maintenance is no longer justified, given the broader adoption of the scientific Python ecosystem. Users who still rely on R from C++ are encouraged to call R directly via https://cran.r-project.org/package=RInside, which is what the ROOT bindings were using internally.
@@ -154,6 +155,13 @@ the cut instead of being selected based on `sqrt(abs(x))`.
 
 ## RooFit
 
+### RooFit::MultiProcess without ZeroMQ, now enabled by default
+
+The `RooFit::MultiProcess` package that implements the parallel gradient minimization with `fitTo(..., RooFit::Parallelize(n))` previously communicated between the forked processes with ZeroMQ sockets, which required building ROOT with `roofit_multiprocess=ON` and the ZeroMQ (with draft API) and cppzmq dependencies.
+The interprocess communication is now implemented directly on top of plain `socketpair()` pipes that are inherited by the forked worker processes, so the ZeroMQ and cppzmq dependencies and the `RooFitZMQ` library are removed entirely.
+Since the feature no longer needs extra dependencies, it is now always built on non-Windows platforms and the `roofit_multiprocess` build option has no effect anymore; it is deprecated and will be removed in ROOT 6.44.
+For implementers of custom `RooFit::MultiProcess::Job` subclasses, the message type in the `Job` interface changed from `zmq::message_t` to the new `RooFit::MultiProcess::Message` byte-buffer class, which supports the same usage patterns.
+
 ### Small changes
 
 * The `RooMinimizer::Strategy` enum has been removed. It named the Minuit strategies that are usually referred to just by integers, but caused confusion because it didn't include the unnamed "Strategy 3". Since people usually set the strategy with integer values anyway, it was decided that the simplest solution to avoid the confusion was simply to remove the `RooMinimizer::Strategy` enum

@@ -153,7 +153,6 @@ ROOT_BUILD_OPTION(pyroot ON "Enable support for automatic Python bindings (PyROO
 ROOT_BUILD_OPTION(pythia8 OFF "Enable support for Pythia 8.x [GPL]")
 ROOT_BUILD_OPTION(qt6web OFF "Enable support for Qt6 web-based display (requires Qt6::WebEngineCore and Qt6::WebEngineWidgets)")
 ROOT_BUILD_OPTION(roofit ON "Build the advanced fitting package RooFit, and RooStats for statistical tests. If xml is available, also build HistFactory.")
-ROOT_BUILD_OPTION(roofit_multiprocess OFF "Build RooFit::MultiProcess and multi-process RooFit::TestStatistics classes (requires ZeroMQ >= 4.3.5 built with -DENABLE_DRAFTS and cppzmq).")
 ROOT_BUILD_OPTION(root7 ON "Build ROOT 7 experimental components of ROOT")
 ROOT_BUILD_OPTION(runtime_cxxmodules ON "Enable runtime support for C++ modules")
 ROOT_BUILD_OPTION(shadowpw OFF "Enable support for shadow passwords")
@@ -304,11 +303,6 @@ if(builtin_openssl AND NOT APPLE)
     message(FATAL_ERROR ">>> Option 'builtin_openssl' is only supported on macOS.")
 endif()
 
-# MultiProcess is not possible on Windows, so fail if it is manually set:
-if(roofit_multiprocess AND WIN32)
-    message(FATAL_ERROR ">>> Option 'roofit_multiprocess' is not supported on Windows.")
-endif()
-
 #---Options depending of CMake Generator-------------------------------------------------------
 if( CMAKE_GENERATOR STREQUAL Ninja)
    set(fortran_defvalue OFF)
@@ -392,6 +386,10 @@ foreach(opt afdsmgrd afs alien bonjour builtin_afterimage builtin_davix builtin_
 endforeach()
 
 #---Deprecated options------------------------------------------------------------------------
+if(DEFINED roofit_multiprocess)
+  message(DEPRECATION ">>> Option 'roofit_multiprocess' has no effect anymore and will be removed in the next release of ROOT: RooFit::MultiProcess no longer needs ZeroMQ and is now always built on all platforms except Windows.")
+endif()
+
 foreach(opt mpi r tmva-pymva)
   if(${opt})
     message(DEPRECATION ">>> Option '${opt}' is deprecated and will be removed in the next release of ROOT. Please contact root-dev@cern.ch should you still need it.")

@@ -1067,32 +1067,6 @@ if (mpi)
   endif()
 endif()
 
-#---Check for ZeroMQ when building RooFit::MultiProcess--------------------------------------------
-
-if (roofit_multiprocess)
-    message(STATUS "Looking for ZeroMQ (libzmq)")
-
-    # Temporarily prefer config mode over module mode, so that a CMake-installed system version
-    # gets detected before looking for an autotools-installed system version (which the
-    # FindZeroMQ.cmake module does).
-    set(CMAKE_FIND_PACKAGE_PREFER_CONFIG_ORIGINAL_VALUE ${CMAKE_FIND_PACKAGE_PREFER_CONFIG})
-    set(CMAKE_FIND_PACKAGE_PREFER_CONFIG TRUE)
-
-    # The fail-on-missing branching is not implemented, and we always look for
-    # ZeroMQ and cppzmq with REQUIRED to fail configuration if not available.
-    # That's because the roofit_multiprocess option can only be deliberately
-    # enabled by the user with roofit_multiprocess=ON, in which case it would
-    # be frustrating to get it auto-disabled on missing dependencies.
-    find_package(ZeroMQ 4.3.5 REQUIRED)
-
-    # Reset default find_package mode
-    set(CMAKE_FIND_PACKAGE_PREFER_CONFIG ${CMAKE_FIND_PACKAGE_PREFER_CONFIG_ORIGINAL_VALUE})
-    unset(CMAKE_FIND_PACKAGE_PREFER_CONFIG_ORIGINAL_VALUE)
-
-    message(STATUS "Looking for ZeroMQ C++ bindings (cppzmq)")
-    find_package(cppzmq REQUIRED)
-endif (roofit_multiprocess)
-
 #---Check for googletest---------------------------------------------------------------
 if (testing OR testsupport)
   if (builtin_gtest)

@@ -8,8 +8,7 @@ set(roofit_legacy_eval_backend ON CACHE BOOL "" FORCE)
 
 add_subdirectory(batchcompute)
 add_subdirectory(codegen)
-if (roofit_multiprocess)
-  add_subdirectory(roofitZMQ)
+if(NOT WIN32)
   add_subdirectory(multiprocess)
 endif()
 add_subdirectory(roofitcore)

@@ -5,6 +5,7 @@
 
 ROOT_LINKER_LIBRARY(RooFitMultiProcess
         src/worker.cxx
+        src/Channel.cxx
         src/Messenger.cxx
         src/ProcessManager.cxx
         src/util.cxx
@@ -18,11 +19,9 @@ ROOT_LINKER_LIBRARY(RooFitMultiProcess
         src/HeatmapAnalyzer.cxx
     LIBRARIES
         Core
-    DEPENDENCIES
-        RooFitZMQ
 )
 
-target_link_libraries(RooFitMultiProcess PUBLIC Hist RooFitZMQ)
+target_link_libraries(RooFitMultiProcess PUBLIC Hist)
 set(RooFitMultiProcess_INCLUDE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/res")
 target_include_directories(RooFitMultiProcess
         PRIVATE ${RooFitMultiProcess_INCLUDE_DIR}
@@ -41,10 +40,13 @@ if(NOT CMAKE_VERSION VERSION_LESS "3.23.0")
         inc/RooFit/MultiProcess/Config.h
         inc/RooFit/MultiProcess/HeatmapAnalyzer.h
         inc/RooFit/MultiProcess/types.h
+        res/RooFit/MultiProcess/Channel.h
         res/RooFit/MultiProcess/JobManager.h
         res/RooFit/MultiProcess/Job.h
+        res/RooFit/MultiProcess/Message.h
         res/RooFit/MultiProcess/Messenger.h
         res/RooFit/MultiProcess/Messenger_decl.h
+        res/RooFit/MultiProcess/Poller.h
         res/RooFit/MultiProcess/ProcessManager.h
         res/RooFit/MultiProcess/ProcessTimer.h
         res/RooFit/MultiProcess/Queue.h