[Bug]: opentelemetry_appender_tracing does not work with blocking otlp exporter

[cortopy]

What happened?

The basic example for opentelemetry_appender_tracing is working fine for me.

The same example also works if I use an OTLP exporter with tonic and Tokio runtime within an async context.

However, if I modify the example for opentelemetry_appender_tracing to use an OTLP exporter with reqwest::blocking, the program enters into a deadlock.

This is the code I'm running:

use opentelemetry::KeyValue;
use opentelemetry_appender_tracing::layer;
use opentelemetry_sdk::{
    logs::{Config, LoggerProvider},
    Resource,
};
use tracing::error;
use tracing_subscriber::prelude::*;

fn main() {
    // This exporter is built with reqwest:blocking and will hang
    let otl_exporter = opentelemetry_otlp::new_exporter()
        .http()
        .build_log_exporter()
        .unwrap();
    let provider: LoggerProvider = LoggerProvider::builder()
        .with_config(
            Config::default().with_resource(Resource::new(vec![KeyValue::new(
                "service.name",
                "log-appender-tracing-example",
            )])),
        )
        .with_simple_exporter(otl_exporter)
        .build();
    let layer = layer::OpenTelemetryTracingBridge::new(&provider);
    tracing_subscriber::registry().with(layer).init();

    error!(name: "my-event-name", target: "my-system", event_id = 20, user_name = "otel", user_email = "otel@opentelemetry.io");
    drop(provider);
}

The opentelemetry-otlp crate is used with both reqwest blocking and tonic within an internal config crate:

opentelemetry-otlp = { version = "0.15.0", features = ["logs", "grpc-tonic", "http-proto", "reqwest-blocking-client", "serialize", "metrics", "trace"] }

API Version

I don't know

SDK Version

0.22.1

What Exporters are you seeing the problem on?

OTLP

Relevant log output

No response

[cijothomas]

I'll take a look today.

[cijothomas]

I was able to easily repro this, but unsure why is this deadlocked, despite using reqwest::blocking client. Will investigate more and get back. There are several errors related to async runtimes and we are actively investigating a proper fix to take care of all of them, including this issue!.

[cijothomas]

This is unrelated to async runtimes, and is caused by exporter itself producing logs which are fed back to opentelemetry.
Test added here: #2199