A simple fork and wait header and library for Windows to be compatible with UNIX-based C/C++ open source softwares.
There is not much libraries available for Windows to use fork and wait, this is one of the key missing features when porting UNIX-based FOSS codes into Windows, especially when developing on a pure Windows platform without UNIX-compatibility environments like WSL, MSYS2 or Cygwin.
While threads as lightweight processes have been widely available and is the preferred approach for multi-tasking, fork and wait functions still have their values when it comes to performing tasks that may kill the main process - there are libraries that actually calls _exit on a spawned thread, the parent process will exit as well!
This library is meant to emulate the basic capabilities of fork and wait, so that it can be a drop-in header and library replacement for code bases that use these functions without being overly intrusive.
What is available right now is barebone minimal as waitpid only supports 0 and >0 pids, -1 and <-1 range were supposed to target the process group that belongs to the specified pid where process group is not supported - they're behaving like 0 and >0 respectively. The only option supported at the moment is WNOHANG.
Check out the wait manpage for more information on the pid argument for waitpid.
- Git
- CMake
- C/C++ compiler (tested on MSVC and LLVM/Clang)
Optional:
- Visual Studio Code
- Ninja
- CCache
- Windows SDK (Comes pre-installed when installing
MSVC,LLVM/Clangwill need this installed separately) - ms-vscode.cmake-tools vscode extension
- Windows 10 x64 (technically Windows Vista) and above, because it uses
NtCreateUserProcess.
NOTE: Linux and Mac OS are not included as they're just a wrapper, this code should still compile and run on those platforms.
When building as a standalone program to test the waters, there will be a few targets available to showcase how fork and waitpid works.
Either hit F5 in vscode after configuring a launch target in CMake Tools, or issue the following commands in the project directory to try out the programs:
cmake -S . -B build -G "Visual Studio 17 2022" -A x64 && cmake --build build
bin\main_c
bin\main_cpp
bin\main_nowait_c
bin\main_nowait_cpp
This library can be added into any code base as a module, its easier if the code base uses modern build tools, eg. CMake, Bazel, Meson, etc.; basically those that support interoperability with CMake.
The easiest approach to use FetchContent in a CMake project:
include(FetchContent)
FetchContent_Declare(
comfork
GIT_REPOSITORY https://github.com/jonnysoe/comfork.git
GIT_TAG main
)
FetchContent_MakeAvailable(comfork)
add_subdirectory(${comfork_SOURCE_DIR})
link_libraries(libcomfork)
Most of these codes were adapted from Hunt & Hackett's documentation in The Definitive Guide To Process Cloning on Windows. The code is basically being refactored to behave like UNIX fork and wait. Check out that page for more information and understanding the caveats of this library.
The fork function has been widely used since ages, it was achieved by invoking an undocumented native API (ntdll) - RtCreateUserProcess, which is the lowest API in user space that can bypass detection controls - refer to Capt. Meelo's blog page for detailed experiments and explanations.
This native API however does not come with a function prototype in any of the headers in Windows SDK, thankfully most of these APIs have been experimented on thoroughly and compiled into the phnt headers by the Process Hacker Project.
NOTE: Despite not encountering any major issues, there may be missing steps that was used in the Winnie-AFL's fork library that is worth adapting.
Hunt & Hackett consolidated a lot of information which is helpful to prepare this library.
Winsider for the phnt native API headers for the elegant native API function call implementation.
Capt. Meelo's blog page for detailed understanding of the native API.
Licensed under the MIT License. See LICENSE.md for more information.
The phnt headers for ntdll is licensed under the CC BY 4.0 License.