[SDK] Implement env var configuration for PeriodicExportingMetricReader

[mathieurobin1]

Fixes #3515

Changes

Implements the configuration of PeriodicExportingMetricReader via environment variables with default values.

It introduces support for:

• OTEL_METRIC_EXPORT_INTERVAL (Duration)
• OTEL_METRIC_EXPORT_TIMEOUT (Timeout)

Known Limitation / Discussion Point:

During implementation, I identified that the existing utility function common::GetDurationEnvironmentVariable is not fully compliant with the specification for Timeout types.

• Specification: A Timeout value of 0 SHOULD be interpreted as "infinite".
• Current Implementation: The underlying parser (GetTimeoutFromString) explicitly rejects a value of 0 as invalid.

To keep the scope of this PR focused on the PeriodicExportingMetricReaderOptions, I have used the existing utility for both environment variables. This means that OTEL_METRIC_EXPORT_TIMEOUT=0 is currently not handled as an infinite timeout but will instead fall back to the default value.

I believe fixing the common utility function should be addressed in a separate issue/PR to ensure it doesn't introduce unintended side effects elsewhere.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: mathieurobin1 / name: Mathieu Robin (2b44323, a1311d1)
• ✅ login: marcalff / name: Marc Alff (10c5437)

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[marcalff]

I changed the title to [SDK], because I use the [CONFIGURATION] tag is for everything related to declarative configuration (aka, config.yaml)

[marcalff]

Thanks for the fix, see minor comments.

[marcalff]

Known Limitation / Discussion Point:

During implementation, I identified that the existing utility function common::GetDurationEnvironmentVariable is not fully compliant with the specification for Timeout types.

* **Specification:** A `Timeout` value of `0` SHOULD be interpreted as "infinite".

* **Current Implementation:** The underlying parser (`GetTimeoutFromString`) explicitly rejects a value of `0` as invalid.

To keep the scope of this PR focused on the PeriodicExportingMetricReaderOptions, I have used the existing utility for both environment variables. This means that OTEL_METRIC_EXPORT_TIMEOUT=0 is currently not handled as an infinite timeout but will instead fall back to the default value.

I believe fixing the common utility function should be addressed in a separate issue/PR to ensure it doesn't introduce unintended side effects elsewhere.

Looks like you found an existing bug.

Please use common::GetDurationEnvironmentVariable so that all duration variables have the same behavior, instead of having multiple and slightly different helpers.

The issue with 0 / infinite can be fixed separately.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.00%. Comparing base (5423b91) to head (2b44323).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3549      +/-   ##
==========================================
+ Coverage   89.99%   90.00%   +0.02%     
==========================================
  Files         219      220       +1     
  Lines        7048     7056       +8     
==========================================
+ Hits         6342     6350       +8     
  Misses        706      706              

Files with missing lines	Coverage Δ
...export/periodic_exporting_metric_reader_options.cc	100.00% <100.00%> (ø)

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[marcalff]

The include-what-you-use failures can be seen in CI, go to "Summary" for the CI job, and download artifacts that contains the full logs.

Search for Warning: include-what-you-use reported diagnostics.

Logs provided below

/home/runner/work/opentelemetry-cpp/opentelemetry-cpp/sdk/test/metrics/periodic_exporting_metric_reader_test.cc should add these lines:
#include <stdlib.h>
#include <ratio>

Also, there is a build break for tests on Windows. See existing tests for how to use setenv.

[mathieurobin1]

Thanks for your feedback, forgot to include env_variables.h for Windows build.
Should be good now :)

[lalitb]

Thanks.

[marcalff]

Build failure in windows CI:

metrics_ostream.obj : error LNK2019: unresolved external symbol "public: __cdecl opentelemetry::v1::sdk::metrics::PeriodicExportingMetricReaderOptions::PeriodicExportingMetricReaderOptions(void)" (??0PeriodicExportingMetricReaderOptions@metrics@sdk@v1@opentelemetry@@QEAA@XZ) referenced in function "void __cdecl `anonymous namespace'::InitMetrics(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &)" (?InitMetrics@?A0x81c1a3c3@@YAXAEBV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@Z) [D:\a\opentelemetry-cpp\opentelemetry-cpp\build\install_test\examples-test\examples\metrics_simple\metrics_ostream_example.vcxproj]

To fix it:

• add OPENTELEMETRY_EXPORT, see file otlp_http_metric_exporter_options.h for an example
• adjust ext/src/dll/input.src if necessary

Since a new patch is needed to fix this, I am adding minor nitpicks as well.

Code looks good overall, will approve once CI is clean.

[marcalff]

LGTM overall.

Thanks for the fix, will approve once CI is clean.

[marcalff]

LGTM.

Thanks for the fix, and the misc cleanup.

[marcalff]

@mathieurobin1 Congratulations on your first patch. Merged.