Proxy meter provider with one time swapping

CHANGELOG.md

@@ -6,6 +6,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://github.com/open-telemetry/opentelemetry-python/compare/v1.5.0-0.24b0...HEAD)
 
+- Return proxy instruments from ProxyMeter
+  [[#2169](https://github.com/open-telemetry/opentelemetry-python/pull/2169)]
 - Make Measurement a concrete class
   ([#2153](https://github.com/open-telemetry/opentelemetry-python/pull/2153))
 - Add metrics API

docs/conf.py

@@ -98,6 +98,8 @@
 nitpick_ignore = [
     ("py:class", "ValueT"),
     ("py:class", "MetricT"),
+    ("py:class", "InstrumentT"),
+    ("py:obj", "opentelemetry.metrics.instrument.InstrumentT"),
     # Even if wrapt is added to intersphinx_mapping, sphinx keeps failing
     # with "class reference target not found: ObjectProxy".
     ("py:class", "ObjectProxy"),

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

@@ -25,7 +25,8 @@
 from abc import ABC, abstractmethod
 from logging import getLogger
 from os import environ
-from typing import Optional, cast
+from threading import Lock
+from typing import List, Optional, cast
 
 from opentelemetry.environment_variables import OTEL_PYTHON_METER_PROVIDER
 from opentelemetry.metrics.instrument import (
@@ -41,7 +42,15 @@
     ObservableGauge,
     ObservableUpDownCounter,
     UpDownCounter,
+    _ProxyCounter,
+    _ProxyHistogram,
+    _ProxyInstrument,
+    _ProxyObservableCounter,
+    _ProxyObservableGauge,
+    _ProxyObservableUpDownCounter,
+    _ProxyUpDownCounter,
 )
+from opentelemetry.util._once import Once
 from opentelemetry.util._providers import _load_provider
 
 _logger = getLogger(__name__)
@@ -71,17 +80,32 @@ def get_meter(
 
 
 class ProxyMeterProvider(MeterProvider):
+    def __init__(self) -> None:
+        self._lock = Lock()
+        self._meters: List[ProxyMeter] = []
+        self._real_meter_provider: Optional[MeterProvider] = None
+
     def get_meter(
         self,
         name,
         version=None,
         schema_url=None,
     ) -> "Meter":
-        if _METER_PROVIDER:
-            return _METER_PROVIDER.get_meter(
-                name, version=version, schema_url=schema_url
-            )
-        return ProxyMeter(name, version=version, schema_url=schema_url)
+        with self._lock:
+            if self._real_meter_provider:
+                return self._real_meter_provider.get_meter(
+                    name, version, schema_url
+                )
+
+            meter = ProxyMeter(name, version=version, schema_url=schema_url)
+            self._meters.append(meter)
+            return meter
+
+    def set_meter_provider(self, meter_provider: MeterProvider) -> None:
+        with self._lock:
+            self._real_meter_provider = meter_provider
+            for meter in self._meters:
+                meter.on_set_real_meter_provider(meter_provider)
 
 
 class Meter(ABC):
@@ -233,43 +257,103 @@ def __init__(
         schema_url=None,
     ):
         super().__init__(name, version=version, schema_url=schema_url)
+        self._lock = Lock()
+        self._instruments: List[_ProxyInstrument] = []
         self._real_meter: Optional[Meter] = None
-        self._noop_meter = _DefaultMeter(
-            name, version=version, schema_url=schema_url
+
+    def on_set_real_meter_provider(
+        self, meter_provider: MeterProvider
+    ) -> None:
+        """Called when a real meter provider is set on the creating ProxyMeterProvider
+
+        Creates a real backing meter for this instance and notifies all created
+        instruments so they can create real backing instruments.
+        """
+        real_meter = meter_provider.get_meter(
+            self._name, self._version, self._schema_url
         )
 
-    @property
-    def _meter(self) -> Meter:
-        if self._real_meter is not None:
-            return self._real_meter
-
-        if _METER_PROVIDER:
-            self._real_meter = _METER_PROVIDER.get_meter(
-                self._name,
-                self._version,
-            )
-            return self._real_meter
-        return self._noop_meter
+        with self._lock:
+            self._real_meter = real_meter
+            # notify all proxy instruments of the new meter so they can create
+            # real instruments to back themselves
+            for instrument in self._instruments:
+                instrument.on_meter_set(real_meter)
 
-    def create_counter(self, *args, **kwargs) -> Counter:
-        return self._meter.create_counter(*args, **kwargs)
+    def create_counter(self, name, unit="", description="") -> Counter:
+        with self._lock:
+            if self._real_meter:
+                return self._real_meter.create_counter(name, unit, description)
+            proxy = _ProxyCounter(name, unit, description)
+            self._instruments.append(proxy)
+            return proxy
 
-    def create_up_down_counter(self, *args, **kwargs) -> UpDownCounter:
-        return self._meter.create_up_down_counter(*args, **kwargs)
+    def create_up_down_counter(
+        self, name, unit="", description=""
+    ) -> UpDownCounter:
+        with self._lock:
+            if self._real_meter:
+                return self._real_meter.create_up_down_counter(
+                    name, unit, description
+                )
+            proxy = _ProxyUpDownCounter(name, unit, description)
+            self._instruments.append(proxy)
+            return proxy
 
-    def create_observable_counter(self, *args, **kwargs) -> ObservableCounter:
-        return self._meter.create_observable_counter(*args, **kwargs)
+    def create_observable_counter(
+        self, name, callback, unit="", description=""
+    ) -> ObservableCounter:
+        with self._lock:
+            if self._real_meter:
+                return self._real_meter.create_observable_counter(
+                    name, callback, unit, description
+                )
+            proxy = _ProxyObservableCounter(
+                name, callback, unit=unit, description=description
+            )
+            self._instruments.append(proxy)
+            return proxy
 
-    def create_histogram(self, *args, **kwargs) -> Histogram:
-        return self._meter.create_histogram(*args, **kwargs)
+    def create_histogram(self, name, unit="", description="") -> Histogram:
+        with self._lock:
+            if self._real_meter:
+                return self._real_meter.create_histogram(
+                    name, unit, description
+                )
+            proxy = _ProxyHistogram(name, unit, description)
+            self._instruments.append(proxy)
+            return proxy
 
-    def create_observable_gauge(self, *args, **kwargs) -> ObservableGauge:
-        return self._meter.create_observable_gauge(*args, **kwargs)
+    def create_observable_gauge(
+        self, name, callback, unit="", description=""
+    ) -> ObservableGauge:
+        with self._lock:
+            if self._real_meter:
+                return self._real_meter.create_observable_gauge(
+                    name, callback, unit, description
+                )
+            proxy = _ProxyObservableGauge(
+                name, callback, unit=unit, description=description
+            )
+            self._instruments.append(proxy)
+            return proxy
 
     def create_observable_up_down_counter(
-        self, *args, **kwargs
+        self, name, callback, unit="", description=""
     ) -> ObservableUpDownCounter:
-        return self._meter.create_observable_up_down_counter(*args, **kwargs)
+        with self._lock:
+            if self._real_meter:
+                return self._real_meter.create_observable_up_down_counter(
+                    name,
+                    callback,
+                    unit,
+                    description,
+                )
+            proxy = _ProxyObservableUpDownCounter(
+                name, callback, unit=unit, description=description
+            )
+            self._instruments.append(proxy)
+            return proxy
 
 
 class _DefaultMeter(Meter):
@@ -329,8 +413,19 @@ def create_observable_up_down_counter(
         )
 
 
-_METER_PROVIDER = None
-_PROXY_METER_PROVIDER = None
+_METER_PROVIDER_SET_ONCE = Once()
+_METER_PROVIDER: Optional[MeterProvider] = None
+_PROXY_METER_PROVIDER = ProxyMeterProvider()
+
+
+def _reset_globals() -> None:
+    """WARNING: only use this for tests."""
+    global _METER_PROVIDER_SET_ONCE  # pylint: disable=global-statement
+    global _METER_PROVIDER  # pylint: disable=global-statement
+    global _PROXY_METER_PROVIDER  # pylint: disable=global-statement
+    _METER_PROVIDER_SET_ONCE = Once()
+    _METER_PROVIDER = None
+    _PROXY_METER_PROVIDER = ProxyMeterProvider()
 
 
 def get_meter(
@@ -350,35 +445,40 @@ def get_meter(
     return meter_provider.get_meter(name, version)
 
 
+def _set_meter_provider(meter_provider: MeterProvider, *, log: bool) -> None:
+    def set_mp() -> None:
+        global _METER_PROVIDER  # pylint: disable=global-statement
+        _METER_PROVIDER = meter_provider
+
+        # gives all proxies real instruments off the newly set meter provider
+        _PROXY_METER_PROVIDER.set_meter_provider(meter_provider)
+
+    did_set = _METER_PROVIDER_SET_ONCE.do_once(set_mp)
+
+    if not did_set:
+        _logger.warning("Overriding of current MeterProvider is not allowed")
+
+
 def set_meter_provider(meter_provider: MeterProvider) -> None:
     """Sets the current global :class:`~.MeterProvider` object.
 
     This can only be done once, a warning will be logged if any furter attempt
     is made.
     """
-    global _METER_PROVIDER  # pylint: disable=global-statement
-
-    if _METER_PROVIDER is not None:
-        _logger.warning("Overriding of current MeterProvider is not allowed")
-        return
-
-    _METER_PROVIDER = meter_provider
+    _set_meter_provider(meter_provider, log=True)
 
 
 def get_meter_provider() -> MeterProvider:
     """Gets the current global :class:`~.MeterProvider` object."""
-    # pylint: disable=global-statement
-    global _METER_PROVIDER
-    global _PROXY_METER_PROVIDER
 
     if _METER_PROVIDER is None:
         if OTEL_PYTHON_METER_PROVIDER not in environ.keys():
-            if _PROXY_METER_PROVIDER is None:
-                _PROXY_METER_PROVIDER = ProxyMeterProvider()
             return _PROXY_METER_PROVIDER
 
-        _METER_PROVIDER = cast(
+        meter_provider = cast(
             "MeterProvider",
             _load_provider(OTEL_PYTHON_METER_PROVIDER, "meter_provider"),
         )
+        _set_meter_provider(meter_provider, log=False)
+
     return _METER_PROVIDER