mingw-std-threads
=================

Implementation of standard C++11 threading classes, which are currently still missing on MinGW GCC.

Target Windows version
----------------------
This implementation should work with Windows XP (regardless of service pack), or newer.
The library automatically detects the version of Windows that is being targeted (at compile time), and selects an implementation that takes advantage of available Windows features.
In MinGW GCC, the target Windows version may optionally be selected by the command-line option `-D _WIN32_WINNT=...`.
Use `0x0600` for Windows Vista, or `0x0601` for Windows 7.
See "[Modifying `WINVER` and `_WIN32_WINNT`](https://docs.microsoft.com/en-us/cpp/porting/modifying-winver-and-win32-winnt)" for more details.

Usage
-----

This is a header-only library. To use, just include the corresponding `mingw.xxx.h file`, where `xxx` would be the name of the standard header that you would normally include.

For example, `#include "mingw.thread.h"` replaces `#include <thread>`.

A `CMakeLists.txt` has also been provided. You can add it to your project by using `add_subdirectory()`, and then this library can be added as your targets' dependency by using `target_link_libraries(YOUR_TARGET PRIVATE mingw_stdthreads)`. By default it just adds a include path, allowing you to include headers using angle brackets (for example `#include <mingw.thread.h>`). But you can also provide options to let it generate "std-like" headers (see next paragraph).

Using "std-like" headers
------------------------

Probably you don't really want to replace all your includes from `#include <header>` to `#include "mingw.header.h"`. So if you are using GCC or clang, here are some ways to make you happy :)

With CMake, you just need to turn on the option `MINGW_STDTHREADS_GENERATE_STDHEADERS` before adding mingw-stdthreads, something like this:
```CMake
option(MINGW_STDTHREADS_GENERATE_STDHEADERS "" ON)
add_subdirectory(mingw_stdthreads)
target_link_libraries(${TARGET} PRIVATE mingw_stdthreads)
```
When CMake generates project files, headers named in the "standard header" way will be generated and added to your include path. Then you can avoid stuffs like `mingw.thread.h`, and keep using `#include <thread>` like always. In addition, `MINGW_STDTHREADS_GENERATED_STDHEADERS` will be defined, you can use this macro to check if those generated headers are actually available.

If you aren't using CMake, you can use one of the three scripts inside [utility_scripts](utility_scripts) directory to manually generate those "std-like" headers. Note that this requires Microsoft Power Shell, so if you are cross-compiling, you would need to install Power Shell.

Compatibility
-------------

This code has been tested to work with MinGW-w64 5.3.0, but should work with any other MinGW version that has the `std` threading classes missing, has C++11 support for lambda functions, variadic templates, and has working mutex helper classes in `<mutex>`.

Switching from the win32-pthread based implementation
-----------------------------------------------------
It seems that recent versions of MinGW-w64 include a Win32 port of pthreads, and have the `std::thread`, `std::mutex`, etc. classes implemented and working based on that compatibility layer.

You could use the built-in pthread implementation of Mingw by using the posix compiler, eg: `x86_64-w64-mingw32-g++-posix` (for Windows 64-bit).

That is a somewhat heavier implementation, as it relies on an abstraction layer, so you may still want to use this implementation for efficiency purposes.
Unfortunately you can't use this library standalone and independent of the system `<mutex>` headers, as it relies on those headers for `std::unique_lock` and other non-trivial utility classes.
In that case you will need to edit the `c++-config.h` file of your MinGW setup and comment out the definition of _GLIBCXX_HAS_GTHREADS.
This will cause the system headers not to define the actual `thread`, `mutex`, etc. classes, but still define the necessary utility classes.

Why MinGW has no threading classes 
----------------------------------
It seems that for cross-platform threading implementation, the GCC standard library relies on the gthreads/pthreads library.
If this library is not available, as is the case with MinGW, the classes `std::thread`, `std::mutex`, `std::condition_variable` are not defined.
However, various usable helper classes are still defined in the system headers.
Hence, this implementation does not re-define them, and instead includes those headers.

