Auto-flush on process exit (#141)

This attaches to the process’s `beforeExit` event (supported in Node.js, Deno, and Bun) when auto-flushing is enabled in order to automatically flush when a program exits. Before, you needed to remember to call `metrics.flush()` manually at the end of your program, which is easy to forget (or not even know about in the first place!).

It also adds a `stop()` method that disables auto-flushing and flushes any remaining buffered metrics.

Fixes #136.

README.md

@@ -114,8 +114,8 @@ Where `options` is an object and can contain the following:
 * `prefix`: Sets a default prefix for all metrics. (optional)
     * Use this to namespace your metrics.
 * `flushIntervalSeconds`: How often to send metrics to Datadog. (optional)
-    * This defaults to 15 seconds. Set it to 0 to disable auto-flushing which
-      means you must call `flush()` manually.
+    * This defaults to 15 seconds. Set it to `0` to disable auto-flushing (which
+      means you must call `flush()` manually).
 * `site`: Sets the Datadog "site", or server where metrics are sent. (optional)
     * Defaults to `datadoghq.com`.
     * See more details on setting your site at:
@@ -197,12 +197,12 @@ metrics.init({
 
 `metrics.gauge(key, value[, tags[, timestamp]])`
 
-Record the current *value* of a metric. The most recent value in
-a given flush interval will be recorded. Optionally, specify a set of
-tags to associate with the metric. This should be used for sum values
-such as total hard disk space, process uptime, total number of active
-users, or number of rows in a database table. The optional timestamp
-is in milliseconds since 1 Jan 1970 00:00:00 UTC, e.g. from `Date.now()`.
+Record the current *value* of a metric. The most recent value since the last
+flush will be recorded. Optionally, specify a set of tags to associate with the
+metric. This should be used for sum values such as total hard disk space,
+process uptime, total number of active users, or number of rows in a database
+table. The optional timestamp is in milliseconds since 1 Jan 1970 00:00:00 UTC,
+e.g. from `Date.now()`.
 
 Example:
 
@@ -284,15 +284,34 @@ metrics.distribution('test.service_time', 0.248);
 
 ### Flushing
 
-`metrics.flush()`
+By default, datadog-metrics will automatically flush, or send accumulated
+metrics to Datadog, at regular intervals, and, in environments that support it,
+before your program exits. (However, if you call `process.exit()` to cause a
+hard exit, datadog-metrics doesn’t get a chance to flush. In this case, you may
+want to call `await metrics.stop()` first.)
+
+You can adjust the interval by using the `flushIntervalSeconds` option. Setting
+it to `0` will disable auto-flushing entirely:
+
+```js
+// Set auto-flush interval to 10 seconds.
+metrics.init({ flushIntervalSeconds: 10 });
+```
+
+You can also send accumulated metrics manually at any time by calling
+`metrics.flush()`.
+
+Please note that, when calling the `BufferedMetricsLogger` constructor directly,
+`flushIntervalSeconds` defaults to `0` instead. When constructing your own
+logger this way, you must expicitly opt-in to auto-flushing by setting a
+positive value.
 
-Calling `flush` sends any buffered metrics to Datadog and returns a promise.
-This function will be called automatically unless you set `flushIntervalSeconds`
-to `0`.
 
-It can be useful to trigger a manual flush by calling if you want to
-make sure pending metrics have been sent before you quit the application
-process, for example.
+#### `metrics.flush()`
+
+Sends any buffered metrics to Datadog and returns a promise. By default,
+`flush()` will be called for you automatically unless you set
+`flushIntervalSeconds` to `0` (see above for more details).
 
 ⚠️ This method used to take two callback arguments for handling successes and
 errors. That form is deprecated and will be removed in a future update:
@@ -318,6 +337,18 @@ metrics.flush()
     .catch((error) => console.log('Flush error:', error)) ;
 ```
 
+#### `metrics.stop(options)`
+
+Stops auto-flushing (if enabled) and flushes any currently buffered metrics.
+This is mainly useful if you want to manually clean up and send remaining
+metrics before hard-quitting your program (usually by calling `process.exit()`).
+Returns a promise for the result of the flush.
+
+Takes an optional object with properties:
+* `flush` (boolean) Whether to flush any remaining metrics after stopping.
+    Defaults to `true`.
+
+
 ## Logging
 
 Datadog-metrics uses the [debug](https://github.com/visionmedia/debug)
@@ -344,7 +375,9 @@ TBD
 
 **New Features:**
 
-TBD
+* When auto-flushing is enabled, metrics are now also flushed before the process exits. In previous versions, you needed to do this manually by calling `metrics.flush()` at the every end of your program.
+
+    You will still need to flush manually if you set `flushIntervalSeconds` to `0` or you are quitting your program by calling `process.exit()` [(which interrupts a variety of operations)](https://nodejs.org/docs/latest/api/process.html#processexitcode).
 
 **Deprecations:**
 

index.js

@@ -35,6 +35,12 @@ function callOnSharedLogger(func) {
     // compiler that this satisfies the types. :(
     return (...args) => {
         if (sharedLogger === null) {
+            // Special case: don't make a new logger just to stop it.
+            // @ts-expect-error TypeScript compiler can't figure this one out.
+            if (func === BufferedMetricsLogger.prototype.stop) {
+                return Promise.resolve(undefined);
+            }
+
             init();
         }
         return func.apply(sharedLogger, args);
@@ -44,6 +50,7 @@ function callOnSharedLogger(func) {
 module.exports = {
     init,
     flush: callOnSharedLogger(BufferedMetricsLogger.prototype.flush),
+    stop: callOnSharedLogger(BufferedMetricsLogger.prototype.stop),
     gauge: callOnSharedLogger(BufferedMetricsLogger.prototype.gauge),
     increment: callOnSharedLogger(BufferedMetricsLogger.prototype.increment),
     histogram: callOnSharedLogger(BufferedMetricsLogger.prototype.histogram),

lib/loggers.js

@@ -7,6 +7,9 @@ const Counter = require('./metrics').Counter;
 const Histogram = require('./metrics').Histogram;
 const Distribution = require('./metrics').Distribution;
 
+const supportsProcessExit = typeof process !== 'undefined'
+    && typeof process.once === 'function';
+
 /**
  * @typedef {object} AggregatorType Buffers metrics to send.
  * @property {(
@@ -103,6 +106,9 @@ class BufferedMetricsLogger {
             opts.site = opts.site || opts.apiHost;
         }
 
+        this.performAutoFlush = this.performAutoFlush.bind(this);
+        this.handleProcessExit = this.handleProcessExit.bind(this);
+
         /** @private */
         this.aggregator = opts.aggregator || new Aggregator(opts.defaultTags);
         /** @private @type {ReporterType} */
@@ -117,34 +123,27 @@ class BufferedMetricsLogger {
         /** @private */
         this.prefix = opts.prefix || '';
         /** @private */
-        this.flushIntervalSeconds = opts.flushIntervalSeconds;
-        /** @private */
         this.histogramOptions = opts.histogram;
 
+        /** @private */
+        this.onError = null;
         if (typeof opts.onError === 'function') {
-            /** @private */
             this.onError = opts.onError;
         } else if (opts.onError != null) {
             throw new TypeError('The `onError` option must be a function');
         }
 
-        if (this.flushIntervalSeconds) {
-            logDebug('Auto-flushing every %d seconds', this.flushIntervalSeconds);
+        /** @private */
+        this.flushTimer = null;
+        /** @private */
+        this.flushIntervalSeconds = 0;
+        if (opts.flushIntervalSeconds < 0) {
+            throw new TypeError(`flushIntervalSeconds must be >= 0 (got: ${opts.flushIntervalSeconds})`);
         } else {
-            logDebug('Auto-flushing is disabled');
+            this.flushIntervalSeconds = opts.flushIntervalSeconds;
         }
 
-        const autoFlushCallback = () => {
-            this.flush();
-            if (this.flushIntervalSeconds) {
-                const interval = this.flushIntervalSeconds * 1000;
-                const tid = setTimeout(autoFlushCallback, interval);
-                // Let the event loop exit if this is the only active timer.
-                if (tid.unref) tid.unref();
-            }
-        };
-
-        autoFlushCallback();
+        this.start();
     }
 
     /**
@@ -326,6 +325,60 @@ class BufferedMetricsLogger {
 
         return result;
     }
+
+    /**
+     * Start auto-flushing metrics.
+     */
+    start() {
+        if (this.flushTimer) {
+            logDebug('Auto-flushing is already enabled');
+        } else if (this.flushIntervalSeconds > 0) {
+            logDebug('Auto-flushing every %d seconds', this.flushIntervalSeconds);
+            if (supportsProcessExit) {
+                process.once('beforeExit', this.handleProcessExit);
+            }
+            this.performAutoFlush();
+        } else {
+            logDebug('Auto-flushing is disabled');
+        }
+    }
+
+    /**
+     * Stop auto-flushing metrics. By default, this will also flush any
+     * currently buffered metrics. You can leave them in the buffer and not
+     * flush by setting the `flush` option to `false`.
+     * @param {Object} [options]
+     * @param {boolean} [options.flush] Whether to flush before returning.
+     *        Defaults to true.
+     * @returns {Promise}
+     */
+    async stop(options) {
+        clearTimeout(this.flushTimer);
+        this.flushTimer = null;
+        if (supportsProcessExit) {
+            process.off('beforeExit', this.handleProcessExit);
+        }
+        if (!options || options.flush) {
+            await this.flush();
+        }
+    }
+
+    /** @private */
+    performAutoFlush() {
+        this.flush();
+        if (this.flushIntervalSeconds) {
+            const interval = this.flushIntervalSeconds * 1000;
+            this.flushTimer = setTimeout(this.performAutoFlush, interval);
+            // Let the event loop exit if this is the only active timer.
+            if (this.flushTimer.unref) this.flushTimer.unref();
+        }
+    }
+
+    /** @private */
+    async handleProcessExit() {
+        logDebug('Auto-flushing before process exits...');
+        this.flush();
+    }
 }
 
 module.exports = {

test-other/types_check.ts

@@ -4,6 +4,7 @@ import {
     reporters,
     init,
     flush,
+    stop,
     gauge,
     increment,
     histogram,
@@ -17,6 +18,8 @@ function useLogger(logger: BufferedMetricsLogger) {
     logger.histogram('histogram.key', 11);
     logger.distribution('distribution.key', 11);
     logger.flush();
+    logger.stop();
+    logger.stop({ flush: false });
 }
 
 useLogger(new BufferedMetricsLogger());
@@ -51,3 +54,5 @@ increment('increment.key');
 histogram('histogram.key', 11);
 distribution('distribution.key', 11);
 flush();
+stop();
+stop({ flush: false });