Add MeterProvider and Meter to the SDK (#2227)

* Add MeterProvider and Meter to the SDK

Fixes #2200

* Add FIXMEs

* Fix docstring

* Add FIXME

* Fix meter return

* Log an error if a force flush fails

* Add FIXME

* Fix lint

* Remove SDK API module

* Unregister

* Fix API names

* Return _DefaultMeter

* Remove properties

* Pass MeterProvider as a parameter to __init__

* Add FIXMEs

* Add FIXMEs

* Fix lint

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

@@ -0,0 +1,216 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# pylint: disable=function-redefined,too-many-ancestors
+
+from abc import ABC, abstractmethod
+from atexit import register, unregister
+from logging import getLogger
+from typing import Optional
+
+from opentelemetry.metrics import Meter as APIMeter
+from opentelemetry.metrics import MeterProvider as APIMeterProvider
+from opentelemetry.metrics import _DefaultMeter
+from opentelemetry.metrics.instrument import (
+    Counter,
+    Histogram,
+    ObservableCounter,
+    ObservableGauge,
+    ObservableUpDownCounter,
+    UpDownCounter,
+)
+from opentelemetry.sdk.resources import Resource
+from opentelemetry.sdk.util.instrumentation import InstrumentationInfo
+
+_logger = getLogger(__name__)
+
+
+class Meter(APIMeter):
+    def __init__(
+        self,
+        instrumentation_info: InstrumentationInfo,
+        meter_provider: APIMeterProvider,
+    ):
+        super().__init__(instrumentation_info)
+        self._instrumentation_info = instrumentation_info
+        self._meter_provider = meter_provider
+
+    def create_counter(self, name, unit=None, description=None) -> Counter:
+        # FIXME implement this method
+        pass
+
+    def create_up_down_counter(
+        self, name, unit=None, description=None
+    ) -> UpDownCounter:
+        # FIXME implement this method
+        pass
+
+    def create_observable_counter(
+        self, name, callback, unit=None, description=None
+    ) -> ObservableCounter:
+        # FIXME implement this method
+        pass
+
+    def create_histogram(self, name, unit=None, description=None) -> Histogram:
+        # FIXME implement this method
+        pass
+
+    def create_observable_gauge(
+        self, name, callback, unit=None, description=None
+    ) -> ObservableGauge:
+        # FIXME implement this method
+        pass
+
+    def create_observable_up_down_counter(
+        self, name, callback, unit=None, description=None
+    ) -> ObservableUpDownCounter:
+        # FIXME implement this method
+        pass
+
+
+class MeterProvider(APIMeterProvider):
+    """See `opentelemetry.metrics.MeterProvider`."""
+
+    def __init__(
+        self,
+        resource: Resource = Resource.create({}),
+        shutdown_on_exit: bool = True,
+    ):
+        self._resource = resource
+        self._atexit_handler = None
+
+        if shutdown_on_exit:
+            self._atexit_handler = register(self.shutdown)
+
+        self._metric_readers = []
+        self._metric_exporters = []
+        self._views = []
+        self._shutdown = False
+
+    def get_meter(
+        self,
+        name: str,
+        version: Optional[str] = None,
+        schema_url: Optional[str] = None,
+    ) -> Meter:
+
+        if self._shutdown:
+            _logger.warning(
+                "A shutdown `MeterProvider` can not provide a `Meter`"
+            )
+            return _DefaultMeter(name, version=version, schema_url=schema_url)
+
+        return Meter(InstrumentationInfo(name, version, schema_url), self)
+
+    def shutdown(self):
+        # FIXME implement a timeout
+
+        if self._shutdown:
+            _logger.warning("shutdown can only be called once")
+            return False
+
+        result = True
+
+        for metric_reader in self._metric_readers:
+            result = result and metric_reader.shutdown()
+
+        for metric_exporter in self._metric_exporters:
+            result = result and metric_exporter.shutdown()
+
+        self._shutdown = True
+
+        if self._atexit_handler is not None:
+            unregister(self._atexit_handler)
+            self._atexit_handler = None
+
+        return result
+
+    def force_flush(self) -> bool:
+
+        # FIXME implement a timeout
+
+        metric_reader_result = True
+        metric_exporter_result = True
+
+        for metric_reader in self._metric_readers:
+            metric_reader_result = (
+                metric_reader_result and metric_reader.force_flush()
+            )
+
+        if not metric_reader_result:
+            _logger.warning("Unable to force flush all metric readers")
+
+        for metric_exporter in self._metric_exporters:
+            metric_exporter_result = (
+                metric_exporter_result and metric_exporter.force_flush()
+            )
+
+        if not metric_exporter_result:
+            _logger.warning("Unable to force flush all metric exporters")
+
+        return metric_reader_result and metric_exporter_result
+
+    def register_metric_reader(self, metric_reader: "MetricReader") -> None:
+        # FIXME protect this method against race conditions
+        self._metric_readers.append(metric_reader)
+
+    def register_metric_exporter(
+        self, metric_exporter: "MetricExporter"
+    ) -> None:
+        # FIXME protect this method against race conditions
+        self._metric_exporters.append(metric_exporter)
+
+    def register_view(self, view: "View") -> None:
+        # FIXME protect this method against race conditions
+        self._views.append(view)
+
+
+class MetricReader(ABC):
+    def __init__(self):
+        self._shutdown = False
+
+    @abstractmethod
+    def collect(self):
+        pass
+
+    def shutdown(self):
+        # FIXME this will need a Once wrapper
+        self._shutdown = True
+
+
+class MetricExporter(ABC):
+    def __init__(self):
+        self._shutdown = False
+
+    @abstractmethod
+    def export(self):
+        pass
+
+    def shutdown(self):
+        # FIXME this will need a Once wrapper
+        self._shutdown = True
+
+
+class View:
+    pass
+
+
+class ConsoleMetricExporter(MetricExporter):
+    def export(self):
+        pass
+
+
+class SDKMetricReader(MetricReader):
+    def collect(self):
+        pass