feat(sdk): add 32-bit platform support using portable-atomic

[neeme-praks-sympower]

Add 32-bit platform support by using portable-atomic for AtomicI64 and AtomicU64 in the metrics module.

Motivation

32-bit ARM platforms (e.g., armv5te-unknown-linux-gnueabi, armv7-unknown-linux-gnueabihf) lack native 64-bit atomic operations. The current use of std::sync::atomic::AtomicI64 and AtomicU64 causes compilation failures on these targets:

error[E0432]: unresolved imports `std::sync::atomic::AtomicI64`, `std::sync::atomic::AtomicU64`

These platforms are common in embedded/IoT environments where lightweight OpenTelemetry collection is valuable. I need this change to unblock streamfold/rotel#304

Solution

Replace std::sync::atomic::{AtomicI64, AtomicU64} with portable_atomic::{AtomicI64, AtomicU64}.

The portable-atomic crate:

• Uses native atomics on 64-bit platforms (zero overhead)
• Provides software-based fallback on 32-bit platforms via the fallback feature
• Is widely used and well-maintained

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: neeme-praks-sympower / name: Neeme Praks (acfb104)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.2%. Comparing base (8cfa981) to head (acfb104).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3345   +/-   ##
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  Coverage   82.2%   82.2%           
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  Files        128     128           
  Lines      24506   24510    +4     
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+ Hits       20147   20151    +4     
  Misses      4359    4359           

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[cijothomas]

https://github.com/open-telemetry/opentelemetry-rust/pull/2773/changes could we follow similar approach from the existing PR to do this conditionally? Or we can ask the original PR to be resurrected.

[cijothomas]

#2773 (comment) If possible, could you address this! Not a blocker, if this helps unblocks other projects. We have a tracking issue for this anyway.

[neeme-praks-sympower]

https://github.com/open-telemetry/opentelemetry-rust/pull/2773/changes could we follow similar approach from the existing PR to do this conditionally? Or we can ask the original PR to be resurrected.

Why?

The portable-atomic crate:

• Uses native atomics on 64-bit platforms (zero overhead)
• Provides software-based fallback on 32-bit platforms via the fallback feature

As it uses native atomics on 64-bit platforms then it is kind of conditional already.

[cijothomas]

https://github.com/open-telemetry/opentelemetry-rust/pull/2773/changes could we follow similar approach from the existing PR to do this conditionally? Or we can ask the original PR to be resurrected.

Why?

The portable-atomic crate:

• Uses native atomics on 64-bit platforms (zero overhead)
• Provides software-based fallback on 32-bit platforms via the fallback feature

As it uses native atomics on 64-bit platforms then it is kind of conditional already.

We try as much as possible to avoid external dependencies by default.

[neeme-praks-sympower]

#2773 (comment) If possible, could you address this! Not a blocker, if this helps unblocks other projects. We have a tracking issue for this anyway.

You mean this comment?

Can you check if this is only place where Atomics were used? It's okay to do it in a follow up, if you are okay with that. (Trying to make sure we do support extra architectures consistently across repo (wherever feasible))

No, there's another usage in test code:

  opentelemetry-sdk/src/logs/logger_provider.rs (lines 306, 312, 322, 681, 705):
  use std::sync::atomic::AtomicU64;  // in #[cfg(test)] module

This is test-only code, so it won't affect 32-bit builds (tests can't run on cross-compiled targets anyway). Or should I fix that as well?

Also docs/metrics.md has an example using AtomicU64, but that's just documentation.

[neeme-praks-sympower]

As it uses native atomics on 64-bit platforms then it is kind of conditional already.

We try as much as possible to avoid external dependencies by default.

Ok, I made it conditional.

[Copilot]

Pull request overview

This PR adds 32-bit platform compatibility for the SDK metrics internals by switching 64-bit atomic counters/gauges to portable-atomic on targets that lack native 64-bit atomic support, unblocking builds on common 32-bit ARM targets.

Changes:

• Conditionally import AtomicI64/AtomicU64 from portable_atomic when target_has_atomic != "64".
• Add a target-specific dependency on portable-atomic with the fallback feature for non-64-bit-atomic platforms.
• Adjust internal metrics unit tests to use boxed dyn AtomicTracker helpers for consistent method dispatch.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
opentelemetry-sdk/src/metrics/internal/mod.rs	Uses portable-atomic atomics on platforms without 64-bit atomics; updates related tests.
opentelemetry-sdk/Cargo.toml	Adds portable-atomic dependency only for targets lacking 64-bit atomics.
opentelemetry-sdk/CHANGELOG.md	Documents the added 32-bit platform support for metrics atomics.

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