fix(sdk): add validation for export_timeout_millis <= 0 in PeriodicExportingMetricReader

[Dotify71]

Description

Fixes #5655

Currently, PeriodicExportingMetricReader validates export_interval_millis during initialization and raises a ValueError if export_interval_millis <= 0. However, export_timeout_millis lacked validation for values <= 0, allowing non-positive integers (0 or negative values) to be passed without error.

Since _ticker() continuously calls self.collect(timeout_millis=self._export_timeout_millis), passing an unvalidated non-positive timeout causes collection timeout errors on every tick cycle.

This PR adds validation for export_timeout_millis <= 0 in PeriodicExportingMetricReader.__init__().

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Unit tests in opentelemetry-sdk/tests/metrics/test_periodic_exporting_metric_reader.py (test_timeout_value_exception_on_zero, test_timeout_value_exception_on_negative).

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[opentelemetry-pr-dashboard]

Pull request dashboard status

Waiting on the author · refreshed 2026-09-20 09:22 UTC

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[Dotify71]

@lzchen This pr is ready for review

[herin049]

Thanks for the PR, if you have future small changes like these, please group them into a single PR.

[Dotify71]

Thanks for the review and approval @herin049 I'll definitely group related small fixes into a single PR next time :))

[Shriprasad-P]

Nice focused PR. Please make sure docs/changelog stay aligned if the repo requires it for this kind of change.

[Dotify71]

All checks passed.... the pr is ready for review :))

[Copilot]

Copilot review overview

🟢 Approval recommended

The validation is correct and adequately tested; the remaining error-message spacing issue is minor.

Review effort: Balanced
Findings: 1

Open (1)

• Error message contains unintended spaces after line continuation · New

What changed in this PR

Adds positive-value validation for metric export timeouts.

Changes:

• Rejects zero and negative export timeouts.
• Adds focused unit tests.
• Adds a changelog entry.

File	Description
.changelog/​5656.fixed	Records the fix.
opentelemetry-sdk/​src/​opentelemetry/​sdk/​metrics/​_internal/​export/​__init__.py	Validates export timeout values.
opentelemetry-sdk/​tests/​metrics/​test_periodic_exporting_metric_reader.py	Tests zero and negative timeout rejection.

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