Make it easier to disable process executor (#7876)

By adding a DISALLOW_PROCESS_EXECUTOR build option it's possible to
conveniently disable the usage of fork() on non-Window platforms that
either don't have fork(), or have an incomplete or inefficient
implementation that is to be considered a last resort only. In the same
commit the DISALLOW_THREAD_EXECUTOR is used for conditionally compiling
the thread executor so that both executors are treated in the same way.

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.