Add PeriodicReaderWithOwnThread (#2292)

Author: cijothomas

opentelemetry-sdk/CHANGELOG.md

@@ -47,9 +47,15 @@
   - Developers creating custom exporters should ensure they import these constructs from the SDK, not the API.
   - [2291](https://github.com/open-telemetry/opentelemetry-rust/pull/2291) Rename `logs_level_enabled flag` to `spec_unstable_logs_enabled`. Please enable this updated flag if the feature is needed. This flag will be removed once the feature is stabilized in the specifications.
 
-
 - **BREAKING**: `Temporality` enum moved from `opentelemetry_sdk::metrics::data::Temporality` to `opentelemetry_sdk::metrics::Temporality`.
 
+- Added a new `PeriodicReader` implementation (`PeriodicReaderWithOwnThread`)
+  that does not rely on an async runtime, and instead creates own Thread. This
+  is under feature flag "experimental_metrics_periodic_reader_no_runtime". The
+  functionality maybe moved into existing PeriodReader or even removed in the
+  future. As of today, this cannot be used as-is with OTLP Metric Exporter or
+  any exporter that require an async runtime.
+
 ## v0.26.0
 Released 2024-Sep-30
 

opentelemetry-sdk/Cargo.toml

@@ -53,6 +53,7 @@ rt-tokio = ["tokio", "tokio-stream"]
 rt-tokio-current-thread = ["tokio", "tokio-stream"]
 rt-async-std = ["async-std"]
 internal-logs = ["tracing"]
+experimental_metrics_periodic_reader_no_runtime = ["metrics"]
 
 [[bench]]
 name = "context"

opentelemetry-sdk/src/metrics/mod.rs

@@ -50,6 +50,8 @@ pub(crate) mod meter;
 mod meter_provider;
 pub(crate) mod noop;
 pub(crate) mod periodic_reader;
+#[cfg(feature = "experimental_metrics_periodic_reader_no_runtime")]
+pub(crate) mod periodic_reader_with_own_thread;
 pub(crate) mod pipeline;
 pub mod reader;
 pub(crate) mod view;
@@ -60,6 +62,8 @@ pub use instrument::*;
 pub use manual_reader::*;
 pub use meter_provider::*;
 pub use periodic_reader::*;
+#[cfg(feature = "experimental_metrics_periodic_reader_no_runtime")]
+pub use periodic_reader_with_own_thread::*;
 pub use pipeline::Pipeline;
 pub use view::*;