PeriodicExportingMetricsReader with value = infinity to support explicit metric collection

CHANGELOG.md

@@ -23,6 +23,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Version 1.15.0/0.36b0 (2022-12-09)
 
+- PeriodicExportingMetricsReader with +Inf interval
+  to support explicit metric collection
+  ([#3059](https://github.com/open-telemetry/opentelemetry-python/pull/3059))
 - Regenerate opentelemetry-proto to be compatible with protobuf 3 and 4
   ([#3070](https://github.com/open-telemetry/opentelemetry-python/pull/3070))
 - Rename parse_headers to parse_env_headers and improve error message

opentelemetry-sdk/src/opentelemetry/sdk/metrics/_internal/export/__init__.py

@@ -23,6 +23,7 @@
 from typing import IO, Callable, Dict, Iterable, Optional
 
 from typing_extensions import final
+import math
 
 # This kind of import is needed to avoid Sphinx errors.
 import opentelemetry.sdk.metrics._internal
@@ -414,7 +415,8 @@ def shutdown(self, timeout_millis: float = 30_000, **kwargs) -> None:
 class PeriodicExportingMetricReader(MetricReader):
     """`PeriodicExportingMetricReader` is an implementation of `MetricReader`
     that collects metrics based on a user-configurable time interval, and passes the
-    metrics to the configured exporter.
+    metrics to the configured exporter. If the time interval is set to `math.inf`, the
+    reader will not invoke periodic collection.
 
     The configured exporter's :py:meth:`~MetricExporter.export` method will not be called
     concurrently.
@@ -463,16 +465,25 @@ def __init__(
         self._shutdown = False
         self._shutdown_event = Event()
         self._shutdown_once = Once()
-        self._daemon_thread = Thread(
-            name="OtelPeriodicExportingMetricReader",
-            target=self._ticker,
-            daemon=True,
-        )
-        self._daemon_thread.start()
-        if hasattr(os, "register_at_fork"):
-            os.register_at_fork(
-                after_in_child=self._at_fork_reinit
-            )  # pylint: disable=protected-access
+        if (
+            self._export_interval_millis > 0
+            and self._export_interval_millis < math.inf
+        ):
+            self._daemon_thread = Thread(
+                name="OtelPeriodicExportingMetricReader",
+                target=self._ticker,
+                daemon=True,
+            )
+            self._daemon_thread.start()
+            if hasattr(os, "register_at_fork"):
+                os.register_at_fork(
+                    after_in_child=self._at_fork_reinit
+                )  # pylint: disable=protected-access
+        elif self._export_interval_millis <= 0:
+            raise ValueError(
+                f"interval value {self._export_interval_millis} is invalid \
+                and needs to be larger than zero and lower than infinity."
+            )
 
     def _at_fork_reinit(self):
         self._daemon_thread = Thread(
@@ -519,7 +530,10 @@ def _shutdown():
             return
 
         self._shutdown_event.set()
-        self._daemon_thread.join(timeout=(deadline_ns - time_ns()) / 10**9)
+        if this._daemon_thread:
+            self._daemon_thread.join(
+                timeout=(deadline_ns - time_ns()) / 10**9
+            )
         self._exporter.shutdown(timeout=(deadline_ns - time_ns()) / 10**6)
 
     def force_flush(self, timeout_millis: float = 10_000) -> bool:

opentelemetry-sdk/tests/metrics/test_periodic_exporting_metric_reader.py

@@ -17,6 +17,7 @@
 from unittest.mock import Mock
 
 from flaky import flaky
+import math
 
 from opentelemetry.sdk.metrics import Counter
 from opentelemetry.sdk.metrics._internal import _Counter
@@ -134,6 +135,32 @@ def test_ticker_called(self):
         self.assertTrue(collect_mock.assert_called_once)
         pmr.shutdown()
 
+    def test_ticker_not_called_on_infinity(self):
+        collect_mock = Mock()
+        exporter = FakeMetricsExporter()
+        exporter.export = Mock()
+        pmr = PeriodicExportingMetricReader(exporter, export_interval_millis=math.inf)
+        pmr._set_collect_callback(collect_mock)
+        sleep(0.1)
+        self.assertTrue(collect_mock.assert_not_called)
+        pmr.shutdown()
+
+    def test_ticker_value_exception_on_zero(self):
+        exporter = FakeMetricsExporter()
+        exporter.export = Mock()
+        self.assertRaises(
+            ValueError, PeriodicExportingMetricReader,
+            exporter, export_interval_millis=0
+        )
+
+    def test_ticker_value_exception_on_negative(self):
+        exporter = FakeMetricsExporter()
+        exporter.export = Mock()
+        self.assertRaises(
+            ValueError, PeriodicExportingMetricReader,
+            exporter, export_interval_millis=-100
+        )
+
     @flaky(max_runs=3, min_passes=1)
     def test_ticker_collects_metrics(self):
         exporter = FakeMetricsExporter()