Metrics: Implement ExportComponent, make ProducerManager abstract. (#1347)

* Metrics: Implement ExportComponent, make ProducerManager abstract.

* Metrics: Add impl and impllite.

* Resolve two TODOs.

* Fix import path, leave a TODO for getMetricRegistry.

* Make NoopMetricProducerManager private. Add missing since tag.

2 files changed, 95 insertions, 0 deletions

diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/export/ExportComponentImpl.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/export/ExportComponentImpl.java
new file mode 100644
index 00000000..173c3aec
--- /dev/null
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/export/ExportComponentImpl.java
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2018, OpenCensus 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.
+ */
+
+package io.opencensus.implcore.metrics.export;
+
+import io.opencensus.metrics.export.ExportComponent;
+import io.opencensus.metrics.export.MetricProducerManager;
+
+/** Implementation of {@link ExportComponent}. */
+public final class ExportComponentImpl extends ExportComponent {
+
+  private final MetricProducerManager metricProducerManager = new MetricProducerManagerImpl();
+
+  @Override
+  public MetricProducerManager getMetricProducerManager() {
+    return metricProducerManager;
+  }
+}
diff --git a/impl_core/src/main/java/io/opencensus/implcore/metrics/export/MetricProducerManagerImpl.java b/impl_core/src/main/java/io/opencensus/implcore/metrics/export/MetricProducerManagerImpl.java
new file mode 100644
index 00000000..fc9db5c1
--- /dev/null
+++ b/impl_core/src/main/java/io/opencensus/implcore/metrics/export/MetricProducerManagerImpl.java
@@ -0,0 +1,64 @@
+/*
+ * Copyright 2018, OpenCensus 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.
+ */
+
+package io.opencensus.implcore.metrics.export;
+
+import com.google.common.base.Preconditions;
+import io.opencensus.metrics.MetricProducer;
+import io.opencensus.metrics.export.MetricProducerManager;
+import java.util.Collections;
+import java.util.LinkedHashSet;
+import java.util.Set;
+import javax.annotation.concurrent.ThreadSafe;
+
+/** Implementation of {@link MetricProducerManager}. */
+@ThreadSafe
+public final class MetricProducerManagerImpl extends MetricProducerManager {
+
+  private volatile Set<MetricProducer> metricProducers =
+      Collections.unmodifiableSet(new LinkedHashSet<MetricProducer>());
+
+  @Override
+  public synchronized void add(MetricProducer metricProducer) {
+    Preconditions.checkNotNull(metricProducer, "metricProducer");
+    // Updating the set of MetricProducers happens under a lock to avoid multiple add or remove
+    // operations to happen in the same time.
+    Set<MetricProducer> newMetricProducers = new LinkedHashSet<MetricProducer>(metricProducers);
+    if (!newMetricProducers.add(metricProducer)) {
+      // The element already present, no need to update the current set of MetricProducers.
+      return;
+    }
+    metricProducers = Collections.unmodifiableSet(newMetricProducers);
+  }
+
+  @Override
+  public synchronized void remove(MetricProducer metricProducer) {
+    Preconditions.checkNotNull(metricProducer, "metricProducer");
+    // Updating the set of MetricProducers happens under a lock to avoid multiple add or remove
+    // operations to happen in the same time.
+    Set<MetricProducer> newMetricProducers = new LinkedHashSet<MetricProducer>(metricProducers);
+    if (!newMetricProducers.remove(metricProducer)) {
+      // The element not present, no need to update the current set of MetricProducers.
+      return;
+    }
+    metricProducers = Collections.unmodifiableSet(newMetricProducers);
+  }
+
+  @Override
+  public Set<MetricProducer> getAllMetricProducer() {
+    return metricProducers;
+  }
+}