measurement residual in SDK

[zhchai]

I am using one instrument to observe memory of multiple processes, process can appear and disappear dynamically.
From test result, measurements of disappeared process are still transmitted out to opentelemetry collector.
Could anyone help?

code snippet

  auto exporter = otlp_exporter::OtlpGrpcMetricExporterFactory::Create(options);

  std::string version{"1.2.0"};
  std::string schema{"https://opentelemetry.io/schemas/1.2.0"};

  // Initialize and set the global MeterProvider
  metric_sdk::PeriodicExportingMetricReaderOptions options;
  options.export_interval_millis = std::chrono::milliseconds(1000);
  options.export_timeout_millis  = std::chrono::milliseconds(500);
  std::unique_ptr<metric_sdk::MetricReader> reader{
      new metric_sdk::PeriodicExportingMetricReader(std::move(exporter), options)};
  auto provider = std::shared_ptr<metrics_api::MeterProvider>(new metric_sdk::MeterProvider());
  auto p        = std::static_pointer_cast<metric_sdk::MeterProvider>(provider);
  p->AddMetricReader(std::move(reader));

  metrics_api::Provider::SetMeterProvider(provider);

void foo_library::observable_process_example(const std::string &name)
{
  std::string observableProcess = name + "_process_metrics_v1";
  auto provider                               = metrics_api::Provider::GetMeterProvider();
  nostd::shared_ptr<metrics_api::Meter> meter = provider->GetMeter(name, "1.2.0");
  auto process_mem_counter = meter->CreateInt64ObservableGauge(observableProcess);
  process_mem_counter->AddCallback(MeasurementFetcher::process_callback, nullptr);
  while(1)
  {
      std::this_thread::sleep_for(std::chrono::seconds(1));
  }
}

  static void process_callback(opentelemetry::metrics::ObserverResult observer, void * /* state */)
  {
    auto observer_int = nostd::get<nostd::shared_ptr<opentelemetry::metrics::ObserverResultT<int64_t>>>(observer);
    for (int n: processes)
    {
        process_memory = getProcessMemory(n); //get processes memory info for pid n
        observer_int ->Observe(process_memory, {{"process_name", process.name},{"pid", n}});
    }
    
  }

[gaochuang]

@open-telemetry/cpp-maintainers @open-telemetry/cpp-approvers](https://github.com/orgs/open-telemetry/teams/cpp-approvers)) Hi, OTEL experts, Could you give some comments about this issuse? Thanks in advance.