Make it easier to disable process executor

By adding a DISALLOW_PROCESS_EXECUTOR build option it's possible
to conveniently disable the usage of fork() on platforms that either
don't have fork(), or have an incomplete or inefficient implementation
that is to be considered a last resort only.

Author: sodero

.github/workflows/CI-unixish.yml

@@ -576,6 +576,8 @@ jobs:
         run: |
           g++ -Ilib -c cli/threadexecutor.cpp -DDISALLOW_THREAD_EXECUTOR
           test -z "$(nm threadexecutor.o)"
+          g++ -Ilib -c cli/processexecutor.cpp -DDISALLOW_PROCESS_EXECUTOR
+          test -z "$(nm processexecutor.o)"
           # TODO: test NO_* defines
 
       - name: Show all ignored files

cli/processexecutor.cpp

@@ -471,4 +471,4 @@ void ProcessExecutor::reportInternalChildErr(const std::string &childname, const
         mErrorLogger.reportErr(errmsg);
 }
 
-#endif // !WIN32
+#endif // HAS_THREADING_MODEL_FORK

cmake/compilerDefinitions.cmake

@@ -50,6 +50,10 @@ if(DISALLOW_THREAD_EXECUTOR)
     add_definitions(-DDISALLOW_THREAD_EXECUTOR)
 endif()
 
+if(DISALLOW_PROCESS_EXECUTOR)
+    add_definitions(-DDISALLOW_PROCESS_EXECUTOR)
+endif()
+
 if(MSVC AND DISABLE_CRTDBG_MAP_ALLOC)
     add_definitions(-DDISABLE_CRTDBG_MAP_ALLOC)
 endif()

cmake/options.cmake

@@ -92,6 +92,10 @@ option(DISALLOW_THREAD_EXECUTOR "Disallow usage of ThreadExecutor for -j"
 if(DISALLOW_THREAD_EXECUTOR AND WIN32)
     message(FATAL_ERROR "Cannot disable usage of ThreadExecutor on Windows as no other executor implementation is currently available")
 endif()
+option(DISALLOW_PROCESS_EXECUTOR "Disallow usage of ProcessExecutor for -j"                   OFF)
+if(DISALLOW_THREAD_EXECUTOR AND DISALLOW_PROCESS_EXECUTOR)
+    message(FATAL_ERROR "Cannot disable both ThreadExecutor and ProcessExecutor")
+endif()
 set(USE_BOOST "Auto" CACHE STRING "Usage of Boost")
 set_property(CACHE USE_BOOST PROPERTY STRINGS Auto Off On)
 option(USE_BOOST_INT128     "Usage of Boost.Multiprecision 128-bit integer for Mathlib"     OFF)

cmake/printInfo.cmake

@@ -78,6 +78,7 @@ if(HAVE_RULES)
 endif()
 message(STATUS)
 message(STATUS "DISALLOW_THREAD_EXECUTOR = ${DISALLOW_THREAD_EXECUTOR}")
+message(STATUS "DISALLOW_PROCESS_EXECUTOR = ${DISALLOW_PROCESS_EXECUTOR}")
 message(STATUS "CMAKE_THREAD_LIBS_INIT = ${CMAKE_THREAD_LIBS_INIT}")
 message(STATUS)
 message(STATUS "USE_BUNDLED_TINYXML2 =  ${USE_BUNDLED_TINYXML2}")

lib/config.h

@@ -161,12 +161,16 @@
 #define HAS_THREADING_MODEL_THREAD
 #define STDCALL __stdcall
 #elif ((defined(__GNUC__) || defined(__sun)) && !defined(__MINGW32__)) || defined(__CPPCHECK__)
+#if !defined(DISALLOW_PROCESS_EXECUTOR)
 #define HAS_THREADING_MODEL_FORK
+#endif
 #if !defined(DISALLOW_THREAD_EXECUTOR)
 #define HAS_THREADING_MODEL_THREAD
 #endif
 #define STDCALL
-#else
+#endif
+
+#if !defined(HAS_THREADING_MODEL_FORK) && !defined(HAS_THREADING_MODEL_THREAD)
 #error "No threading model defined"
 #endif
 

releasenotes.txt

@@ -43,5 +43,6 @@ Infrastructure & dependencies:
 - The official Windows binary is now built against Boost 1.89 for increased performance.
 - Updated to simplecpp 1.6.2
 - The Visual Studio builds not longer set the `WIN32` define.
+- Added `DISALLOW_PROCESS_EXECUTOR` for building without fork().
 
 The changes focus heavily on stability (crash fixes), C/C++ compatibility, reducing false positives, and improving performance.