Fix MeterProvider destructor warning when Shutdown() called manually

[Copilot]

Problem

When MeterProvider::Shutdown() is called manually, the destructor still calls Shutdown() again, which causes MeterContext to emit a warning:

[MeterContext::Shutdown] Shutdown can be invoked only once.

This creates unnecessary noise in logs when users properly shut down their meter providers manually before destruction.

Root Cause

The MeterProvider destructor unconditionally calls context_->Shutdown() without checking if shutdown has already been performed:

MeterProvider::~MeterProvider()
{
  if (context_)
  {
    context_->Shutdown();  // Always calls shutdown
  }
}

Solution

This PR implements the same pattern used by other components in the codebase like BatchSpanProcessor and SimpleLogRecordProcessor:

1. Added IsShutdown() method to MeterContext - Allows checking shutdown state without side effects
2. Added atomic<bool> is_shutdown_ member - Tracks shutdown state independently of the shutdown latch
3. Updated MeterProvider destructor - Only calls Shutdown() if not already shut down
4. Preserved existing behavior - Manual duplicate shutdown calls still emit warnings as expected

Changes

Before:

MeterProvider::~MeterProvider()
{
  if (context_)
  {
    context_->Shutdown();  // Always warns if shutdown was called manually
  }
}

After:

MeterProvider::~MeterProvider()
{
  if (context_ && !context_->IsShutdown())
  {
    context_->Shutdown();  // Only shutdown if not already done
  }
}

Testing

• ✅ Existing tests pass without destructor warnings
• ✅ New ShutdownTwice test validates the fix
• ✅ Manual duplicate shutdown calls still warn appropriately
• ✅ All metrics tests continue to pass

Before Fix

[Warning] File: .../meter_context.cc:178 [MeterContext::Shutdown] Shutdown can be invoked only once.

After Fix

No warnings from destructor when Shutdown() was called manually.

Fixes #3511.

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[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 89.97%. Comparing base (62ba4de) to head (4de0bd5). :warning: Report is 44 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3513      +/-   ##
==========================================
- Coverage   90.01%   89.97%   -0.03%     
==========================================
  Files         219      219              
  Lines        7044     7047       +3     
==========================================
  Hits         6340     6340              
- Misses        704      707       +3     

Files with missing lines	Coverage Δ
sdk/src/metrics/meter_context.cc	78.21% <100.00%> (+0.88%)	:arrow_up:
sdk/src/metrics/meter_provider.cc	87.18% <100.00%> (ø)

... and 3 files with indirect coverage changes

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[ThomsonTan]

Please fix the below format error from CI.

The following files have changes:
sdk/test/metrics/meter_provider_sdk_test.cc
diff --git a/sdk/test/metrics/meter_provider_sdk_test.cc b/sdk/test/metrics/meter_provider_sdk_test.cc
index 2254be0..bf05572 100644
--- a/sdk/test/metrics/meter_provider_sdk_test.cc
+++ b/sdk/test/metrics/meter_provider_sdk_test.cc
@@ -328,12 +328,12 @@ TEST(MeterProvider, ShutdownTwice)
 {
   // Test that calling Shutdown twice doesn't emit warnings
   MeterProvider mp;
-  
+
   // First shutdown should succeed
   EXPECT_TRUE(mp.Shutdown());
-  
+
   // Second shutdown should also succeed without warnings
   EXPECT_TRUE(mp.Shutdown());
-  
+
   // Destructor should not emit warnings either since we already shut down
 }
Error: Process completed with exit code 1.

[Copilot]

Please fix the below format error from CI.

...

Fixed the formatting error by removing trailing whitespace from the test file. Commit aff62f5

[marcalff]

See related:

• https://github.com/open-telemetry/community/issues/2851

[marcalff]

/easycla

[Reneg973]

I guess the problem is located deeper in the design of Shutdown(). It should be clarified whether it should be possible to add new collectors after Shutdown(), which is currently possible. This opens the next design flaw, GetCollectors() is public API, which would allow access to already shut down collectors. Additionally, MeterContext is derived from std::enable_shared_from_this<>, which implies a possible shared state. But then everyone holding this shared pointer is allowed to call ShutDown().