Add gauge example (#460)

* Add basic gauge example

* Record process uptime directly

* Use Queue related example for derived gauge

Author: mayurkale22

examples/gauge/derived-gauge-quickstart.js

@@ -0,0 +1,59 @@
+/**
+ * Copyright 2019, 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.
+ */
+
+/**
+ * This is an example shows how to create a Derived Gauge metric. This gauge is
+ * self sufficient once created
+ */
+
+const { Metrics, MeasureUnit } = require('@opencensus/core');
+
+// [UNCOMMENT THIS BLOCK to visualize the data =======================]
+// // Enable OpenCensus exporters to export gauges to Stackdriver Monitoring.
+// const { StackdriverStatsExporter } = require('@opencensus/exporter-stackdriver');
+// const exporter = new StackdriverStatsExporter({ projectId: 'projectId' });
+// const { globalStats } = require('@opencensus/core');
+// globalStats.registerExporter(exporter);
+// [END setup_exporter ==============================================]
+
+// To instrument a queue's depth.
+class QueueManager {
+  constructor () { this.depth = 0; }
+  getValue () { return this.depth; }
+  addJob () { this.depth++; }
+}
+
+// a registry is a collection of metric objects.
+const metricRegistry = Metrics.getMetricRegistry();
+
+// application labels - applied to each metric / gauge.
+const labelKeys = [{ key: 'VM', description: 'VM Description' }];
+const labelValues = [{ value: 'localhost' }];
+
+// a new gauge instance - builds a new Int64 gauge to be added to the registry.
+const metricOptions = {
+  description: 'Number of active handles',
+  unit: MeasureUnit.UNIT,
+  labelKeys: labelKeys
+};
+const gauge = metricRegistry.addDerivedInt64Gauge('active_handles_total', metricOptions);
+
+const queue = new QueueManager();
+queue.addJob();
+
+// The value of the gauge is observed from the obj whenever metrics are
+// collected. In this case it will be 1.
+gauge.createTimeSeries(labelValues, queue);

examples/gauge/gauge-quickstart.js

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+/**
+ * Copyright 2019, 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.
+ */
+
+/**
+ * This is an example shows how to create a Gauge metric and manually set or
+ * add value of the gauge. Gauge metric API is to report instantaneous
+ * measurement of an int64/double value. Gauges can go both up and down. The
+ * gauges values can be negative.
+ */
+
+const { Metrics, MeasureUnit } = require('@opencensus/core');
+
+// [UNCOMMENT THIS BLOCK to visualize the data =======================]
+// // Enable OpenCensus exporters to export gauges to Stackdriver Monitoring.
+// const { StackdriverStatsExporter } = require('@opencensus/exporter-stackdriver');
+// const exporter = new StackdriverStatsExporter({ projectId: 'projectId' });
+// const { globalStats } = require('@opencensus/core');
+// globalStats.registerExporter(exporter);
+// [END setup_exporter ==============================================]
+
+// a registry is a collection of metric objects.
+const metricRegistry = Metrics.getMetricRegistry();
+
+// application labels - applied to each metric / gauge.
+const labelKeys = [{ key: 'VM', description: 'VM Description' }];
+const labelValues = [{ value: 'localhost' }];
+
+// a new gauge instance - builds a new Int64 gauge to be added to the registry.
+const metricOptions = {
+  description: 'The number of seconds the current Node.js process has been running',
+  unit: MeasureUnit.SEC,
+  labelKeys: labelKeys
+};
+const gauge = metricRegistry.addDoubleGauge('process_uptime', metricOptions);
+
+// It is recommended to keep a reference of a point for manual operations.
+const point = gauge.getOrCreateTimeSeries(labelValues);
+point.set(process.uptime());
+
+for (let i = 0; i < 1000000000; i++) {
+  // do some work here
+}
+
+point.set(process.uptime());