std::condition_variable_any::notify_one() stucks.

[denprog]

➜  src emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.34 (57b21b8fdcbe3ebb523178b79465254668eab408)
clang version 17.0.0 (https://github.com/llvm/llvm-project a031f72187ce495b9faa4ccf99b1e901a3872f4b)

In my app I use a main thread:

std::thread main_loop = std::thread(&Document::MainLoop, this);

In this thread I wait for a conditional variable:

std::unique_lock<std::recursive_mutex> lock(tasks_mutex);
if (tasks.empty() && undos.empty() && redos.empty())
{
       printf("Wait on conditional\n");
       if (next_circle.wait_for(lock, caret_settings.blink_delay * 1ms) == std::cv_status::timeout) //wait for tasks
       {
            caret->Blink();
            continue;
       }
}

Somewhere in the code I notify it:

next_circle.notify_one();

So, in the Linux app it works fine. In the webasm app it works so:

1. Waiting on "next_circle.wait_for()" is infinite every time.
2. Code "next_circle.notify_one()" passes about 4 times, after it hangs forever. I tried to debug it, the debugger shows waiting in the conditional variable's mutex... But who is the second thread who locks it I can't find.

My question is: how should I work with conditional variables? What's wrong with this code? Are C++ conditional variables supported in emscripten?

[tlively]

Everything should mostly "just work" here, although it's sometimes possible to get Emscripten-specific deadlocks when you do some operation that proxies to the main thread while the main thread is waiting for a lock. Are you using -sPROXY_TO_PTHREAD? If not, does adding that option fix the problem?

[denprog]

If I add this param, I get error in main():

SDL_CreateWindowAndRenderer(400, 400, 0, &w, &renderer);
yutovo_web.worker.js:197 Uncaught TypeError: Cannot read properties of undefined (reading 'createShader')

This is part of my CMakeLists.txt:

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s NO_EXIT_RUNTIME=1")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s USE_SDL=2")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s USE_SDL_TTF=2")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s USE_SDL_IMAGE=2")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s USE_FREETYPE=1")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --shell-file ${CMAKE_CURRENT_SOURCE_DIR}/../shell_minimal.html")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread -s USE_PTHREADS=1 -s PTHREAD_POOL_SIZE=4")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} --preload-file ./fonts")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexperimental-library")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s PROXY_TO_PTHREAD")