Fix Prometheus server crash on listening to already used port

CHANGELOG.md

@@ -22,6 +22,7 @@ Increment the:
 * [CI] Enforce copyright check in CI [#1965](https://github.com/open-telemetry/opentelemetry-cpp/pull/1965)
 * [SEMANTIC CONVENTIONS] Upgrade to version 1.18.0
   [#1974](https://github.com/open-telemetry/opentelemetry-cpp/pull/1974)
+* Fix Prometheus server crash on listening to already used port [#1986](https://github.com/open-telemetry/opentelemetry-cpp/pull/1986)
 
 ## [1.8.2] 2023-01-31
 

examples/prometheus/README.md

@@ -11,31 +11,12 @@
 
 ## Export metrics from the application
 
-It is highly recommended to go over the [ostream-metrics](../metrics_simple/README.md)
-doc before following along this document.
-
 Run the application with:
 
 ```sh
 bazel run //examples/prometheus:prometheus_example
 ```
 
-The main difference between the [ostream-metrics](../metrics_simple/README.md)
-example with this one is that the line below is replaced:
-
-```cpp
-std::unique_ptr<metric_sdk::PushMetricExporter> exporter{
-    new exportermetrics::OStreamMetricExporter};
-
-```
-
-with
-
-```cpp
-std::unique_ptr<metrics_sdk::PushMetricExporter> exporter{
-    new metrics_exporter::PrometheusExporter(opts)};
-```
-
 OpenTelemetry `PrometheusExporter` will export
 data via the endpoint defined by
 `metrics_exporter::PrometheusExporterOptions::url`,
@@ -46,8 +27,7 @@ graph LR
 
 subgraph SDK
   MeterProvider
-  MetricReader[PeriodicExportingMetricReader]
-  PrometheusExporter["PrometheusExporter<br/>(http://localhost:9464/)"]
+  MetricReader["PrometheusExporter<br/>(http://localhost:9464/)"]
 end
 
 subgraph API
@@ -56,7 +36,7 @@ end
 
 Instrument --> | Measurements | MeterProvider
 
-MeterProvider --> | Metrics | MetricReader --> | Pull | PrometheusExporter
+MeterProvider --> | Metrics | MetricReader
 ```
 
 Also, for our learning purpose, we use a while-loop to keep recoring random

examples/prometheus/main.cc

@@ -78,7 +78,7 @@ void CleanupMetrics()
 int main(int argc, char **argv)
 {
   std::string example_type;
-  std::string addr{"localhost:8080"};
+  std::string addr{"localhost:9464"};
   if (argc == 1)
   {
     std::puts("usage: $prometheus_example <example type> <url>");

exporters/prometheus/src/collector.cc

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #include "opentelemetry/exporters/prometheus/collector.h"
+#include "opentelemetry/sdk/common/global_log_handler.h"
 
 namespace metric_sdk = opentelemetry::sdk::metrics;
 
@@ -27,6 +28,9 @@ std::vector<prometheus_client::MetricFamily> PrometheusCollector::Collect() cons
 {
   if (reader_->IsShutdown())
   {
+    OTEL_INTERNAL_LOG_WARN(
+        "[Prometheus Exporter] Collect: "
+        "Exporter is shutdown, cann't invoke collect operation.");
     return {};
   }
   collection_lock_.lock();

exporters/prometheus/src/exporter.cc

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0
 
 #include "opentelemetry/exporters/prometheus/exporter.h"
+#include "opentelemetry/sdk/common/global_log_handler.h"
 
 OPENTELEMETRY_BEGIN_NAMESPACE
 
@@ -16,7 +17,19 @@ namespace metrics
  */
 PrometheusExporter::PrometheusExporter(const PrometheusExporterOptions &options) : options_(options)
 {
-  exposer_   = std::unique_ptr<::prometheus::Exposer>(new ::prometheus::Exposer{options_.url});
+  try
+  {
+    exposer_ = std::unique_ptr<::prometheus::Exposer>(new ::prometheus::Exposer{options_.url});
+  }
+  catch (const std::exception &ex)
+  {
+    exposer_.reset(nullptr);
+    OTEL_INTERNAL_LOG_ERROR("[Prometheus Exporter] "
+                            << "Can't initialize prometheus exposer with endpoint: " << options_.url
+                            << "\nError: " << ex.what());
+    Shutdown();  // set MetricReader in shutdown state.
+    return;
+  }
   collector_ = std::shared_ptr<PrometheusCollector>(new PrometheusCollector(this));
 
   exposer_->RegisterCollectable(collector_);
@@ -36,7 +49,8 @@ bool PrometheusExporter::OnForceFlush(std::chrono::microseconds /* timeout */) n
 
 bool PrometheusExporter::OnShutDown(std::chrono::microseconds /* timeout */) noexcept
 {
-  exposer_->RemoveCollectable(collector_);
+  if (exposer_ != nullptr)
+    exposer_->RemoveCollectable(collector_);
   return true;
 }
 

exporters/prometheus/test/exporter_test.cc

@@ -28,11 +28,12 @@ using opentelemetry::sdk::metrics::InstrumentType;
 TEST(PrometheusExporter, InitializeConstructorIsNotShutdown)
 {
   PrometheusExporterOptions options;
-  options.url = "localhost:8081";
+  options.url = "localhost:8084";
   PrometheusExporter exporter(options);
   // // Asserts that the exporter is not shutdown.
-  // ASSERT_TRUE(!exporter.IsShutdown());
+  ASSERT_TRUE(exporter.IsShutdown());
   exporter.Shutdown();
+  ASSERT_TRUE(exporter.IsShutdown());
 }
 
 /**