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May 07, 2022

Logging Thread ID in Rust

Last updated at: Aug 18, 2022

Recently, I am working on implementing concurrent operations for B+ Tree index in Rust. Dealing with concurrency bugs can be pain in the ass and and being able to print the thread ID along with by my debug message definitely help me understand the interleaving operations better.

Here’s how I learn to do it using env_logger crate and tracing crate.

Env Logger

I was using env_logger to log my message. Upon realizing that std::thread::current() allow me to get the information of the current thread executing my code, and it have the id() method, I start to inject the info into my log as needed:

let thread_id = std::thread::current().id();
info!("{}: fetch page {page_id}", thread_id);

Soon, I realize that I can format the log records by default using the Builder::format method. So I ended up with this:

use std::io::Write;

env_logger::builder()
    .format(|buf, record| {
        let ts = buf.timestamp_micros();
        writeln!(
            buf,
            "{}: {:?}: {}: {}",
            ts,
            std::thread::current().id(),
            buf.default_level_style(record.level())
                .value(record.level()),
            record.args()
        )
    })
    .init();

which will log my message in the following format:

2022-05-07T07:26:33.119900Z: ThreadId(7): INFO: fetch page 1

Tracing

Later on, I switch to using tracing and the setup is much simpler as follow:

tracing_subscriber::fmt().with_thread_ids(true).init();

It turns out tracing_subscriber formatter come with the with_thread_ids method to include your thread id in your logs once set to true. Here’s how the messsage look like:

May 07 15:38:42.197  INFO ThreadId(01) sqlite::table::test: fetch page 1

There are more configuration methods that might be useful for you such as with_thread_names, so do have a look at the documentation!

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