How to separate logs by thread?

[Kakapio]

I'm currently using tracing for a program where 10 threads are run all at the same time. A ton of logs are emitted asynchronously so there's a lot of noise from each thread's logs being shoved together out of order. I wanted to ask if there's an easy way to separate logs by thread? I need to do this in order to debug my program. I hacked together some code to accomplish this but it randomly crashes because it tries to drop a span that doesn't exist.

My current approach is to just generate a subscriber like so:

pub(crate) fn create_subscriber(&self) -> impl Subscriber {
    // Create non-blocking writer for file logging
    let file_appender = tracing_appender::rolling::RollingFileAppender::new(
      tracing_appender::rolling::Rotation::NEVER,
      &self.log_path,
      "TESTING",
    );

    let (non_blocking_file, _guard) = tracing_appender::non_blocking(file_appender);

    // Necessary due to the filter closure below.
    let name = self.name.clone();

    // Create a format for specific logs
    let file_layer = fmt::layer()
      .with_target(true)
      .with_thread_ids(true)
      .with_level(true)
      .with_ansi(false)
      .with_file(true)
      .with_line_number(true)
      .with_writer(non_blocking_file)
      // Filter based on name in the target or fields
      .with_filter(filter_fn(move |metadata| {
        if let Some(field) = metadata.fields().field("name") {
          field.to_string().contains(&name)
        } else {
          false
        }
      }))
      .with_filter(LevelFilter::INFO);

    Registry::default().with(file_layer)
  }
}

and use it in the method that each thread runs like so:

// Create a scoped logger for this repository
let _repo_guard = tracing::subscriber::set_default(my_logger.create_subscriber());

[kaffarell]

You could just create a custom Layer (https://docs.rs/tracing-subscriber/latest/tracing_subscriber/layer/index.html) and then check a task_local storage (https://docs.rs/tokio/latest/tokio/macro.task_local.html) in the on_event function. e.g. something like this:

struct CustomSubscriber {}

impl<S: Subscriber> Layer<S> for CustomSubscriber {
    fn on_event(&self, event: &Event<'_>, ctx: Context<'_, S>) {
        LOG.with(|flag| {
            if *flag {
                // log
            }
        })
    }
}

fn main() {
    tracing_subscriber::registry()
        .with(CustomSubscriber {})
        .init();

    let _ = std::thread::spawn(|| {
        LOG.sync_scope(true, || {
            tracing::info!("info");
        })
    })
    .join();
}

[QnnOkabayashi]

I wrote tracing-forest 2 years ago for this exact purpose. I haven't updated it much but it's been used by several people consistently for those two years.

[Kakapio]

A decent enough work-around. I tried tracing-forest but it was not helpful for my use-case. I believe it was difficult to get it to write logs with separation as I was still running into the dropped span error. My logs are also quite complex so the formatting would be very confusing.