Fix:1676 Segfault when short export period is used for metrics

sdk/src/metrics/meter_context.cc

@@ -67,6 +67,7 @@ void MeterContext::AddMeter(std::shared_ptr<Meter> meter)
 bool MeterContext::Shutdown() noexcept
 {
   bool result = true;
+  // Shutdown only once.
   if (!shutdown_latch_.test_and_set(std::memory_order_acquire))
   {
 
@@ -80,25 +81,27 @@ bool MeterContext::Shutdown() noexcept
       OTEL_INTERNAL_LOG_WARN("[MeterContext::Shutdown] Unable to shutdown all metric readers");
     }
   }
+  else
+  {
+    OTEL_INTERNAL_LOG_WARN("[MeterContext::Shutdown] Shutdown can be invoked only once.");
+  }
   return result;
 }
 
 bool MeterContext::ForceFlush(std::chrono::microseconds timeout) noexcept
 {
   // TODO - Implement timeout logic.
   bool result = true;
-  if (!shutdown_latch_.test_and_set(std::memory_order_acquire))
+  // Simultaneous flush not allowed.
+  const std::lock_guard<opentelemetry::common::SpinLockMutex> locked(forceflush_lock_);
+  for (auto &collector : collectors_)
   {
-
-    for (auto &collector : collectors_)
-    {
-      bool status = std::static_pointer_cast<MetricCollector>(collector)->ForceFlush(timeout);
-      result      = result && status;
-    }
-    if (!result)
-    {
-      OTEL_INTERNAL_LOG_WARN("[MeterContext::ForceFlush] Unable to ForceFlush all metric readers");
-    }
+    bool status = std::static_pointer_cast<MetricCollector>(collector)->ForceFlush(timeout);
+    result      = result && status;
+  }
+  if (!result)
+  {
+    OTEL_INTERNAL_LOG_WARN("[MeterContext::ForceFlush] Unable to ForceFlush all metric readers");
   }
   return result;
 }

sdk/test/metrics/meter_provider_sdk_test.cc

@@ -81,7 +81,7 @@ TEST(MeterProvider, GetMeter)
   ASSERT_EQ(m4, m5);
   ASSERT_NE(m3, m6);
 
-  // Should be an sdk::trace::Tracer with the processor attached.
+  // Should be an sdk::metrics::Meter
 #  ifdef OPENTELEMETRY_RTTI_ENABLED
   auto sdkMeter1 = dynamic_cast<Meter *>(m1.get());
 #  else
@@ -98,5 +98,9 @@ TEST(MeterProvider, GetMeter)
   std::unique_ptr<MeterSelector> meter_selector{new MeterSelector("name1", "version1", "schema1")};
 
   mp1.AddView(std::move(instrument_selector), std::move(meter_selector), std::move(view));
+
+  // cleanup properly without crash
+  mp1.ForceFlush();
+  mp1.Shutdown();
 }
 #endif