Is Ruby's stdlib Logger class thread-safe?

A quick look at logger.rb reveals code such as the following:

def write(message)  @mutex.synchronize do    if @shift_age and @dev.respond_to?(:stat)      begin        check_shift_log      rescue        raise Logger::ShiftingError.new("Shifting failed. #{$!}")      end    end    @dev.write(message)  endend

So while I can't vouch for whether it gets thread-safety correct, I can confirm that it is making a concerted effort to do it right!

P.S. It's often easy to answer questions like this for yourself by reading the code :-)

Below is my original response, which is actually wrong. Read Nemo157's comment below. I left it here for reference only.

Original:

I don't think it matters. All implementations of Ruby that I know of so far effectively run one thread at a time anyway: It does allow you to start many threads, but only one thread runs at a time per process.

Some Ruby classes are designed to be thread safe, but don't explicitly say so in words of one syllable in their documentation. Unlike documentation in other programming languages such as PHP.

I remember being asked whether Queue was thread-safe on Stack Overflow, and even though it was, the documentation didn't spell that out.