Is it safe to call fmtlog::poll from the queue-full callback?

[gh-andre]

Provided that fmtlog::poll(true) is called by a single thread from within the callback function set with fmtlog::setLogQFullCB, is it safe to call it there, like in the example below?

Asking in terms of reentrancy - would it interfere with any thread local storage, global values, etc, within fmtlog?

void logFullCB(void*)
{
    fmtlog::poll(true);
}

int main()
{
  fmtlog::setLogQFullCB(&logFullCB, nullptr);
  for (int i = 0; i < 1'000'000; i++) {
    std::string str(1000, ' ');
    logio("{:d} log q full cb test: {:s}", i, str);
  }
  return 0;
}

Thanks

[MengRao]

Yes, you may call fmtlog::poll in logFullCB, but be aware that fmtlog::poll is not thread-safe, so you should make sure it's not being called in another thread at the same time.
Also note that logFullCB is invoked synchronously in the logio macro in your example. In more complicated cases where multiple threads are using fmtlog for logging and logFullCB could be triggered concurrently, user should ensure thread-safety of fmtlog::poll.

[gh-andre]

This is just a simple example to demonstrate the intent. In actual code I do use synchronization to make sure fmtlog::poll is always called on a single thread.

Initially I used a separate thread for this, but it takes a bit of time to synchronize between threads and calling fmtlog::poll right in the callback, with proper synchronization for multiple logging calls, is the most optimal way to flush the buffers. It works well, but I wanted to make sure I'm not missing anything. Thanks for confirming.