tracing_subscriber: Add `with_os_thread_ids`

[tgross35]

Feature Request

Crates

tracing_subscriber

Motivation

On the current nightly, the thread ID is now printed as part of the panic messages:

thread 'main' (13) panicked at src/main.rs:2:5:
explicit panic
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

It would be nice to have an easy way to coordinate this with tracing events, as well as with debugger output and process managers.

Proposal

Add the following:

• Layer::with_os_thread_ids
• SubscriberBuilder::with_os_thread_ids
• Format::with_os_thread_ids

This matches with_thread_ids in each of the same places.

Unfortunately there is no way to get the OS TID in std: not sure whether this is a dealbreaker or not. It is a simple libc call on most platforms:

https://github.com/rust-lang/rust/blob/898aff704d6f0d00343f21d31b8b9bfac8e43007/library/std/src/sys/pal/unix/thread.rs#L401-L455

https://github.com/rust-lang/rust/blob/898aff704d6f0d00343f21d31b8b9bfac8e43007/library/std/src/sys/pal/windows/thread.rs#L130-L136

(there is a gettid crate but it is broken, and I don't think there is any need to pull in a crate for 3-6 definitions).

Alternatives

with_thread_ids could be changed to emit the OS TID.