C++ support for std::thread

[davidthings]

Hi, I have some code built for Linux and ESP32 which use the C++ classes which wrap pthread and others. I want to use this code on a RP2040 in FreeRTOS SMP.

I added Lab-Project-FreeRTOS-POSIX include and source files and can confirm the pthreads functions work.

void* threadFunction(void* arg) {
    while ( 1 ) {
        std::cout << "pthread is working!" << std::endl;
        printf("pthread is working!\n");
        vTaskDelay(1000);
    }
    return nullptr;
}
...
    pthread_t thread;

    // Create a new thread that runs 'threadFunction'
    if (pthread_create(&thread, nullptr, threadFunction, nullptr) != 0) {
        std::cerr << "Error: pthread_create failed!" << std::endl;
        return 1;
    }
...

std::thread things however do not compile. (confirming #include <thread> is there)

The error when I try to declare one is:

system.cpp:408:10: error: 'thread' in namespace 'std' does not name a type
  408 |     std::thread thread_;
      |          ^~~~~~

When I try to straight up use one, eg.

std::thread t([]{ std::cout << "Threading is supported!\n"; });
t.join(); 

the error is

system.cpp:430:14: error: 'thread' is not a member of 'std'
  430 |         std::thread t([]{ std::cout << "Threading is supported!\n"; });

So it really looks like it doesn't want to see it!

In Linux environments, the magic -pthread option turns the multithreading lights on, but I guess that's not the right approach here.

I have half a day into this now, and have been having the "almost there" feeling for the whole time. I started delving into the source code for std::thread and quickly realized I was in over my head. So I think it's time to ask for help.

Is there something simple I can add / define in FreeRTOSConfig.h, CMakeLists.txt or anywhere else to magically turn the lights on?

I'm happy to make a minimal example and dump code in here, but I'm kinda hoping there's a "Oh! You have to define XXXX to make it work" answer.

If it is easy / obvious, it seems to me that allowing this as a pico option somewhere would be really great and would unlock a lot of C++ compatibility.