feat(eachAsync): dedupe async iteration with a common helper

Author: mbroadst

lib/core/connection/pool.js

@@ -19,6 +19,7 @@ const apm = require('./apm');
 const Buffer = require('safe-buffer').Buffer;
 const connect = require('./connect');
 const updateSessionFromResponse = require('../sessions').updateSessionFromResponse;
+const eachAsync = require('../utils').eachAsync;
 
 var DISCONNECTED = 'disconnected';
 var CONNECTING = 'connecting';
@@ -635,42 +636,35 @@ Pool.prototype.unref = function() {
 
 // Destroy the connections
 function destroy(self, connections, options, callback) {
-  let connectionCount = connections.length;
-  function connectionDestroyed() {
-    connectionCount--;
-    if (connectionCount > 0) {
-      return;
-    }
-
-    // clear all pool state
-    self.inUseConnections = [];
-    self.availableConnections = [];
-    self.connectingConnections = 0;
-    self.executing = false;
-    self.queue = [];
-    self.reconnectConnection = null;
-    self.numberOfConsecutiveTimeouts = 0;
-    self.connectionIndex = 0;
-    self.retriesLeft = self.options.reconnectTries;
-    self.reconnectId = null;
-
-    // Set state to destroyed
-    stateTransition(self, DESTROYED);
-    if (typeof callback === 'function') {
-      callback(null, null);
-    }
-  }
+  eachAsync(
+    connections,
+    (conn, cb) => {
+      CONNECTION_EVENTS.forEach(eventName => conn.removeAllListeners(eventName));
+      conn.destroy(options, cb);
+    },
+    err => {
+      if (err) {
+        if (typeof callback === 'function') callback(err, null);
+        return;
+      }
 
-  if (connectionCount === 0) {
-    connectionDestroyed();
-    return;
-  }
+      // clear all pool state
+      self.inUseConnections = [];
+      self.availableConnections = [];
+      self.connectingConnections = 0;
+      self.executing = false;
+      self.queue = [];
+      self.reconnectConnection = null;
+      self.numberOfConsecutiveTimeouts = 0;
+      self.connectionIndex = 0;
+      self.retriesLeft = self.options.reconnectTries;
+      self.reconnectId = null;
 
-  // Destroy all connections
-  connections.forEach(conn => {
-    CONNECTION_EVENTS.forEach(eventName => conn.removeAllListeners(eventName));
-    conn.destroy(options, connectionDestroyed);
-  });
+      // Set state to destroyed
+      stateTransition(self, DESTROYED);
+      if (typeof callback === 'function') callback(null, null);
+    }
+  );
 }
 
 /**
@@ -755,43 +749,39 @@ Pool.prototype.destroy = function(force, callback) {
  */
 Pool.prototype.reset = function(callback) {
   const connections = this.availableConnections.concat(this.inUseConnections);
-  let connectionCount = connections.length;
-  const connectionDestroyed = () => {
-    connectionCount--;
-    if (connectionCount > 0) {
-      return;
-    }
+  eachAsync(
+    connections,
+    (conn, cb) => {
+      CONNECTION_EVENTS.forEach(eventName => conn.removeAllListeners(eventName));
+      conn.destroy({ force: true }, cb);
+    },
+    err => {
+      if (err) {
+        if (typeof callback === 'function') {
+          callback(err, null);
+          return;
+        }
+      }
 
-    // clear all pool state
-    this.inUseConnections = [];
-    this.availableConnections = [];
-    this.connectingConnections = 0;
-    this.executing = false;
-    this.reconnectConnection = null;
-    this.numberOfConsecutiveTimeouts = 0;
-    this.connectionIndex = 0;
-    this.retriesLeft = this.options.reconnectTries;
-    this.reconnectId = null;
-
-    // create an initial connection, and kick off execution again
-    _createConnection(this);
-
-    if (typeof callback === 'function') {
-      callback(null, null);
+      // clear all pool state
+      this.inUseConnections = [];
+      this.availableConnections = [];
+      this.connectingConnections = 0;
+      this.executing = false;
+      this.reconnectConnection = null;
+      this.numberOfConsecutiveTimeouts = 0;
+      this.connectionIndex = 0;
+      this.retriesLeft = this.options.reconnectTries;
+      this.reconnectId = null;
+
+      // create an initial connection, and kick off execution again
+      _createConnection(this);
+
+      if (typeof callback === 'function') {
+        callback(null, null);
+      }
     }
-  };
-
-  // if we already have no connections, just reset state and callback
-  if (connectionCount === 0) {
-    connectionDestroyed();
-    return;
-  }
-
-  // destroy all connections
-  connections.forEach(conn => {
-    CONNECTION_EVENTS.forEach(eventName => conn.removeAllListeners(eventName));
-    conn.destroy({ force: true }, connectionDestroyed);
-  });
+  );
 };
 
 // Prepare the buffer that Pool.prototype.write() uses to send to the server

lib/core/utils.js

@@ -116,6 +116,37 @@ function isPromiseLike(maybePromise) {
   return maybePromise && typeof maybePromise.then === 'function';
 }
 
+/**
+ * Applies the function `eachFn` to each item in `arr`, in parallel.
+ *
+ * @param {array} arr an array of items to asynchronusly iterate over
+ * @param {function} eachFn A function to call on each item of the array. The callback signature is `(item, callback)`, where the callback indicates iteration is complete.
+ * @param {function} callback The callback called after every item has been iterated
+ */
+function eachAsync(arr, eachFn, callback) {
+  if (arr.length === 0) {
+    callback(null);
+    return;
+  }
+
+  const length = arr.length;
+  let completed = 0;
+  function eachCallback(err) {
+    if (err) {
+      callback(err, null);
+      return;
+    }
+
+    if (++completed === length) {
+      callback(null);
+    }
+  }
+
+  for (let idx = 0; idx < length; ++idx) {
+    eachFn(arr[idx], eachCallback);
+  }
+}
+
 module.exports = {
   uuidV4,
   calculateDurationInMs,
@@ -124,5 +155,6 @@ module.exports = {
   retrieveEJSON,
   retrieveKerberos,
   maxWireVersion,
-  isPromiseLike
+  isPromiseLike,
+  eachAsync
 };