implement pull metric reader

Alex Boten · Alex Boten · commit 680e662caed0 · 2022-02-28T12:10:37.000-08:00
diff --git a/exporter/opentelemetry-exporter-prometheus/src/opentelemetry/exporter/prometheus/__init__.py b/exporter/opentelemetry-exporter-prometheus/src/opentelemetry/exporter/prometheus/__init__.py
@@ -27,28 +27,29 @@
 
 .. code:: python
 
-    from opentelemetry import metrics
-    from opentelemetry.exporter.prometheus import PrometheusMetricExporter
-    from opentelemetry.sdk.metrics import Meter
     from prometheus_client import start_http_server
 
+    from opentelemetry._metrics import get_meter_provider, set_meter_provider
+    from opentelemetry.exporter.prometheus import PrometheusMetricExporter
+    from opentelemetry.sdk._metrics import MeterProvider
+    from opentelemetry.sdk._metrics.export import PullMetricExporterReader
+
     # Start Prometheus client
     start_http_server(port=8000, addr="localhost")
 
-    # Meter is responsible for creating and recording metrics
-    metrics.set_meter_provider(MeterProvider())
-    meter = metrics.get_meter(__name__)
     # exporter to export metrics to Prometheus
     prefix = "MyAppPrefix"
     exporter = PrometheusMetricExporter(prefix)
-    # Starts the collect/export pipeline for metrics
-    metrics.get_meter_provider().start_pipeline(meter, exporter, 5)
+    reader = PullMetricExporterReader(exporter)
+
+    # Meter is responsible for creating and recording metrics
+    set_meter_provider(MeterProvider(metric_readers=[reader]))
+    meter = get_meter_provider().get_meter(__name__)
 
     counter = meter.create_counter(
         "requests",
-        "number of requests",
         "requests",
-        int,
+        "number of requests",
     )
 
     # Labels are used to identify key-values that are associated with a specific
@@ -71,12 +72,12 @@
 from prometheus_client import core
 
 from opentelemetry.sdk._metrics.export import (
-    MetricExporter,
     MetricExportResult,
+    PullMetricExporter,
 )
 from opentelemetry.sdk._metrics.point import Gauge, Histogram, Metric, Sum
 
-logger = logging.getLogger(__name__)
+_logger = logging.getLogger(__name__)
 
 
 def _convert_buckets(metric: Metric) -> Sequence[Tuple[str, int]]:
@@ -93,7 +94,7 @@ def _convert_buckets(metric: Metric) -> Sequence[Tuple[str, int]]:
     return buckets
 
 
-class PrometheusMetricExporter(MetricExporter):
+class PrometheusMetricExporter(PullMetricExporter):
     """Prometheus metric exporter for OpenTelemetry.
 
     Args:
@@ -102,7 +103,8 @@ class PrometheusMetricExporter(MetricExporter):
     """
 
     def __init__(self, prefix: str = ""):
-        self._collector = _CustomCollector(prefix)
+        self._collect = None
+        self._collector = _CustomCollector(self.collect, prefix)
         core.REGISTRY.register(self._collector)
 
     def export(self, metrics: Sequence[Metric]) -> MetricExportResult:
@@ -118,8 +120,9 @@ class _CustomCollector:
     https://github.com/prometheus/client_python#custom-collectors
     """
 
-    def __init__(self, prefix: str = ""):
+    def __init__(self, callback, prefix: str = ""):
         self._prefix = prefix
+        self._callback = callback
         self._metrics_to_export = collections.deque()
         self._non_letters_nor_digits_re = re.compile(
             r"[^\w]", re.UNICODE | re.IGNORECASE
@@ -135,6 +138,8 @@ def collect(self) -> None:
         Collect is invoked every time a prometheus.Gatherer is run
         for example when the HTTP endpoint is invoked by Prometheus.
         """
+        if self._callback:
+            self._callback()
 
         while self._metrics_to_export:
             for export_record in self._metrics_to_export.popleft():
@@ -193,7 +198,7 @@ def _translate_to_prometheus(
                 labels=label_values, buckets=buckets, sum_value=value
             )
         else:
-            logger.warning("Unsupported metric type. %s", type(metric.point))
+            _logger.warning("Unsupported metric type. %s", type(metric.point))
         return prometheus_metric
 
     def _sanitize(self, key: str) -> str:
diff --git a/exporter/opentelemetry-exporter-prometheus/tests/test_prometheus_exporter.py b/exporter/opentelemetry-exporter-prometheus/tests/test_prometheus_exporter.py
@@ -19,8 +19,8 @@
 from prometheus_client.core import CounterMetricFamily, GaugeMetricFamily
 
 from opentelemetry.exporter.prometheus import (
-    _CustomCollector,
     PrometheusMetricExporter,
+    _CustomCollector,
 )
 from opentelemetry.sdk._metrics.export import MetricExportResult
 from opentelemetry.sdk._metrics.point import AggregationTemporality, Histogram
@@ -79,7 +79,7 @@ def test_histogram_to_prometheus(self):
             attributes={"histo": 1},
         )
 
-        collector = _CustomCollector("testprefix")
+        collector = _CustomCollector(mock.Mock(), "testprefix")
         collector.add_metrics_data([record])
         result_bytes = generate_latest(collector)
         result = result_bytes.decode("utf-8")
@@ -95,7 +95,7 @@ def test_sum_to_prometheus(self):
             description="testdesc",
             unit="testunit",
         )
-        collector = _CustomCollector("testprefix")
+        collector = _CustomCollector(mock.Mock(), "testprefix")
         collector.add_metrics_data([record])
 
         for prometheus_metric in collector.collect():
@@ -123,7 +123,7 @@ def test_gauge_to_prometheus(self):
             description="testdesc",
             unit="testunit",
         )
-        collector = _CustomCollector("testprefix")
+        collector = _CustomCollector(mock.Mock(), "testprefix")
         collector.add_metrics_data([record])
 
         for prometheus_metric in collector.collect():
@@ -148,13 +148,13 @@ def test_invalid_metric(self):
             description="testdesc",
             unit="testunit",
         )
-        collector = _CustomCollector("testprefix")
+        collector = _CustomCollector(mock.Mock(), "testprefix")
         collector.add_metrics_data([record])
         collector.collect()
         self.assertLogs("opentelemetry.exporter.prometheus", level="WARNING")
 
     def test_sanitize(self):
-        collector = _CustomCollector("testprefix")
+        collector = _CustomCollector(mock.Mock(), "testprefix")
         self.assertEqual(
             collector._sanitize("1!2@3#4$5%6^7&8*9(0)_-"),
             "1_2_3_4_5_6_7_8_9_0___",
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/_metrics/export/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/_metrics/export/__init__.py
@@ -21,6 +21,8 @@
 from threading import Event, Thread
 from typing import IO, Callable, Iterable, Optional, Sequence
 
+from typing_extensions import final
+
 from opentelemetry.context import (
     _SUPPRESS_INSTRUMENTATION_KEY,
     attach,
@@ -176,3 +178,34 @@ def _shutdown():
         self._daemon_thread.join()
         self._exporter.shutdown()
         return True
+
+
+class PullMetricExporter(MetricExporter):
+    @final
+    def collect(self) -> None:
+        if self._collect:
+            self._collect()
+
+
+class PullMetricExporterReader(MetricReader):
+    def __init__(
+        self,
+        exporter: PullMetricExporter,
+    ):
+        super().__init__(preferred_temporality=exporter.preferred_temporality)
+        self._exporter = exporter
+        self._exporter._collect = self.collect
+
+    def _receive_metrics(self, metrics: Iterable[Metric]) -> None:
+        if metrics is None:
+            return
+        token = attach(set_value(_SUPPRESS_INSTRUMENTATION_KEY, True))
+        try:
+            self._exporter.export(metrics)
+        except Exception as e:  # pylint: disable=broad-except,invalid-name
+            _logger.exception("Exception while exporting metrics %s", str(e))
+        detach(token)
+
+    def shutdown(self) -> bool:
+        self._exporter.shutdown()
+        return True
