Radian hangs when printing from multi-threaded C++ code

[oelhammouchi]

Hello, thank you very much for this amazing project! I've been experiencing an issue with radian hanging indefinitely when printing from threads in C++ that can't manage to debug. So far, it's only occurred when using the rcppspdlog library with the r_sink_mt logger designed to silence R CMD check warnings about printing to console. I've verified that it doesn't happen in the vanilla console.

He's an example snippet to illustrate the issue. If I compile the following function using Rcpp

#include <spdlog/fmt/ostr.h>
#include <RcppSpdlog>
#include <thread>

//' @export
// [[Rcpp::export]]
void testRsink() {
  std::string logname = "test_logger";
  auto sp = spdlog::get(logname);
  if (sp == nullptr) sp = spdlog::r_sink_mt(logname);
  spdlog::set_default_logger(sp);
  spdlog::set_pattern("[%H:%M:%S.%f] [%n] [%^%L%$] [thread %t] %v");
  spdlog::set_level(spdlog::level::warn);

  std::function warn_in_thread = [&]() {
    spdlog::warn("Something went wrong");
    return;
  };

  std::vector<std::thread> pool(4);
  for (std::thread& thrd : pool) {
    thrd = std::thread(warn_in_thread);
  }

  for (std::thread& thrd : pool) {
    thrd.join();
  }
}

and then run it in the R console, I get the output

> testRsink()
[16:21:25.695730] [test_logger] [W] [thread 8447909] Something went wrong
[16:21:25.695746] [test_logger] [W] [thread 8447910] Something went wrong
[16:21:25.695756] [test_logger] [W] [thread 8447911] Something went wrong
[16:21:25.695776] [test_logger] [W] [thread 8447912] Something went wrong

whereas radian just hangs without printing anything.

I guess it must have something to do with the infamous threading implementation in Python, but I'm not sure. Any idea how (or if) this can be solved?