I have a program where I have multiple threads writing to the same io. The multithreaded writing function is generic over the writer type W: Write + Send, but the type defaults to stdout.

Currently, I handle this by sending an Arc<Mutex<W>> to each thread. That works fine, and I should probably just leave it at that.

However, I noticed that the Stdout type itself contains a Mutex. So, my current solution locks twice on each write: First it locks the mutex I created to access the Stdout, and then it locks the Stdout. I wonder if there is a way to only make it lock once for Stdout, while still having the function be generic over writer types.

I've tried the following things:

• Share an Arc<W> where for<'a> &'a T: Write. This doesn't work, because even though &W: Write, I still need a mutable reference to actually call .write.
• Require W: Write + Send + Clone, then clone the W and send a copy to each thread. However, Stdout does not implement Clone.

Is there a way to handle this?

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