Add capture to open file descriptors in system metrics instrumentation

CHANGELOG.md

@@ -23,6 +23,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#2631](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/2631))
 - `opentelemetry-instrumentation-system-metrics` Permit to use psutil 6.0+.
   ([#2630](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/2630))
+- `opentelemetry-instrumentation-system-metrics` Add support for capture open file descriptors
+  ([#2652](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/2652))
 
 ### Breaking changes
 

instrumentation/opentelemetry-instrumentation-system-metrics/src/opentelemetry/instrumentation/system_metrics/__init__.py

@@ -117,6 +117,7 @@
     "process.runtime.thread_count": None,
     "process.runtime.cpu.utilization": None,
     "process.runtime.context_switches": ["involuntary", "voluntary"],
+    "process.open_file_descriptor.count": None,
 }
 
 if sys.platform == "darwin":
@@ -169,6 +170,7 @@ def __init__(
         self._runtime_thread_count_labels = self._labels.copy()
         self._runtime_cpu_utilization_labels = self._labels.copy()
         self._runtime_context_switches_labels = self._labels.copy()
+        self._open_file_descriptor_count_labels = self._labels.copy()
 
     def instrumentation_dependencies(self) -> Collection[str]:
         return _instruments
@@ -395,9 +397,25 @@ def _instrument(self, **kwargs):
                 unit="switches",
             )
 
+        if "process.open_file_descriptor.count" in self._config:
+            self._meter.create_observable_up_down_counter(
+                name="process.open_file_descriptor.count",
+                callbacks=[self._get_open_file_descriptors],
+                description="Number of file descriptors in use by the process.",
+            )
+
     def _uninstrument(self, **__):
         pass
 
+    def _get_open_file_descriptors(
+        self, options: CallbackOptions
+    ) -> Iterable[Observation]:
+        """Observer callback for Number of file descriptors in use by the process"""
+        yield Observation(
+            self._proc.num_fds(),
+            self._open_file_descriptor_count_labels.copy(),
+        )
+
     def _get_system_cpu_time(
         self, options: CallbackOptions
     ) -> Iterable[Observation]:

instrumentation/opentelemetry-instrumentation-system-metrics/tests/test_system_metrics.py

@@ -118,12 +118,13 @@ def test_system_metrics_instrument(self):
             f"process.runtime.{self.implementation}.thread_count",
             f"process.runtime.{self.implementation}.context_switches",
             f"process.runtime.{self.implementation}.cpu.utilization",
+            "process.open_file_descriptor.count",
         ]
 
         if self.implementation == "pypy":
-            self.assertEqual(len(metric_names), 20)
-        else:
             self.assertEqual(len(metric_names), 21)
+        else:
+            self.assertEqual(len(metric_names), 22)
         observer_names.append(
             f"process.runtime.{self.implementation}.gc_count",
         )
@@ -842,3 +843,14 @@ def test_runtime_cpu_percent(self, mock_process_cpu_percent):
         self._test_metrics(
             f"process.runtime.{self.implementation}.cpu.utilization", expected
         )
+
+    @mock.patch("psutil.Process.num_fds")
+    def test_open_file_descriptor_count(self, mock_process_num_fds):
+        mock_process_num_fds.configure_mock(**{"return_value": 3})
+
+        expected = [_SystemMetricsResult({}, 3)]
+        self._test_metrics(
+            "process.open_file_descriptor.count",
+            expected,
+        )
+        mock_process_num_fds.assert_called()