Verify previous point is returned for cumulative instruments (#2773)

* Verify previous point is returned for cumulative instruments

Fixes #2755

* Reject non-cumulative temporalities for Prometheus metric reader

* Add test case for InMemoryMetricReader

* Fix prometheus import paths

* Remove parameters for Prometheus init

* Add sleep for windows tests

* Add temporality overriding dictionary

Author: ocelotl

exporter/opentelemetry-exporter-prometheus/src/opentelemetry/exporter/prometheus/__init__.py

@@ -77,7 +77,16 @@
 )
 from prometheus_client.core import Metric as PrometheusMetric
 
+from opentelemetry.sdk.metrics import Counter
+from opentelemetry.sdk.metrics import Histogram as HistogramInstrument
+from opentelemetry.sdk.metrics import (
+    ObservableCounter,
+    ObservableGauge,
+    ObservableUpDownCounter,
+    UpDownCounter,
+)
 from opentelemetry.sdk.metrics.export import (
+    AggregationTemporality,
     Gauge,
     Histogram,
     HistogramDataPoint,
@@ -113,7 +122,17 @@ class PrometheusMetricReader(MetricReader):
     """
 
     def __init__(self, prefix: str = "") -> None:
-        super().__init__()
+
+        super().__init__(
+            preferred_temporality={
+                Counter: AggregationTemporality.CUMULATIVE,
+                UpDownCounter: AggregationTemporality.CUMULATIVE,
+                HistogramInstrument: AggregationTemporality.CUMULATIVE,
+                ObservableCounter: AggregationTemporality.CUMULATIVE,
+                ObservableUpDownCounter: AggregationTemporality.CUMULATIVE,
+                ObservableGauge: AggregationTemporality.CUMULATIVE,
+            }
+        )
         self._collector = _CustomCollector(prefix)
         REGISTRY.register(self._collector)
         self._collector._callback = self.collect

exporter/opentelemetry-exporter-prometheus/tests/test_prometheus_exporter.py

@@ -23,6 +23,7 @@
     PrometheusMetricReader,
     _CustomCollector,
 )
+from opentelemetry.sdk.metrics import MeterProvider
 from opentelemetry.sdk.metrics.export import (
     AggregationTemporality,
     Histogram,
@@ -51,7 +52,7 @@ def setUp(self):
     def test_constructor(self):
         """Test the constructor."""
         with self._registry_register_patch:
-            exporter = PrometheusMetricReader("testprefix")
+            exporter = PrometheusMetricReader(prefix="testprefix")
             self.assertEqual(exporter._collector._prefix, "testprefix")
             self.assertTrue(self._mock_registry_register.called)
 
@@ -286,3 +287,16 @@ def test_check_value(self):
         self.assertEqual(collector._check_value(True), "true")
         self.assertEqual(collector._check_value(False), "false")
         self.assertEqual(collector._check_value(None), "null")
+
+    def test_multiple_collection_calls(self):
+
+        metric_reader = PrometheusMetricReader(prefix="prefix")
+        provider = MeterProvider(metric_readers=[metric_reader])
+        meter = provider.get_meter("getting-started", "0.1.2")
+        counter = meter.create_counter("counter")
+        counter.add(1)
+        result_0 = list(metric_reader._collector.collect())
+        result_1 = list(metric_reader._collector.collect())
+        result_2 = list(metric_reader._collector.collect())
+        self.assertEqual(result_0, result_1)
+        self.assertEqual(result_1, result_2)

opentelemetry-sdk/tests/metrics/test_in_memory_metric_reader.py

@@ -12,11 +12,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from time import sleep
 from unittest import TestCase
 from unittest.mock import Mock
 
 from opentelemetry.metrics import Observation
-from opentelemetry.sdk.metrics import MeterProvider
+from opentelemetry.sdk.metrics import Counter, MeterProvider
 from opentelemetry.sdk.metrics.export import (
     AggregationTemporality,
     InMemoryMetricReader,
@@ -106,3 +107,50 @@ def test_integration(self):
             ),
             1,
         )
+
+    def test_cumulative_multiple_collect(self):
+
+        reader = InMemoryMetricReader(
+            preferred_temporality={Counter: AggregationTemporality.CUMULATIVE}
+        )
+        meter = MeterProvider(metric_readers=[reader]).get_meter("test_meter")
+        counter = meter.create_counter("counter1")
+        counter.add(1, attributes={"key": "value"})
+
+        reader.collect()
+
+        number_data_point_0 = list(
+            reader._metrics_data.resource_metrics[0]
+            .scope_metrics[0]
+            .metrics[0]
+            .data.data_points
+        )[0]
+
+        # Windows tests fail without this sleep because both time_unix_nano
+        # values are the same.
+        sleep(0.1)
+        reader.collect()
+
+        number_data_point_1 = list(
+            reader._metrics_data.resource_metrics[0]
+            .scope_metrics[0]
+            .metrics[0]
+            .data.data_points
+        )[0]
+
+        self.assertEqual(
+            number_data_point_0.attributes, number_data_point_1.attributes
+        )
+        self.assertEqual(
+            number_data_point_0.start_time_unix_nano,
+            number_data_point_1.start_time_unix_nano,
+        )
+        self.assertEqual(
+            number_data_point_0.start_time_unix_nano,
+            number_data_point_1.start_time_unix_nano,
+        )
+        self.assertEqual(number_data_point_0.value, number_data_point_1.value)
+        self.assertGreater(
+            number_data_point_1.time_unix_nano,
+            number_data_point_0.time_unix_nano,
+        )