refactor(topology): use sets for timer management

Author: mbroadst

lib/core/sdam/topology.js

@@ -178,9 +178,9 @@ class Topology extends EventEmitter {
       clusterTime: null,
 
       // timer management
-      monitorTimers: [],
-      iterationTimers: [],
-      connectionTimers: []
+      monitorTimers: new Set(),
+      iterationTimers: new Set(),
+      connectionTimers: new Set()
     };
 
     // amend options for server instance creation
@@ -334,14 +334,9 @@ class Topology extends EventEmitter {
     }
 
     // clear all existing monitor timers
-    this.s.monitorTimers.map(timer => clearTimeout(timer));
-    this.s.monitorTimers = [];
-
-    this.s.iterationTimers.map(timer => clearTimeout(timer));
-    this.s.iterationTimers = [];
-
-    this.s.connectionTimers.map(timer => clearTimeout(timer));
-    this.s.connectionTimers = [];
+    drainTimerQueue(this.s.monitorTimers);
+    drainTimerQueue(this.s.iterationTimers);
+    drainTimerQueue(this.s.connectionTimers);
 
     if (this.s.sessionPool) {
       this.s.sessions.forEach(session => session.endSession());
@@ -427,9 +422,7 @@ class Topology extends EventEmitter {
       return;
     }
 
-    // clear out any existing iteration timers
-    this.s.iterationTimers.map(timer => clearTimeout(timer));
-    this.s.iterationTimers = [];
+    drainTimerQueue(this.s.iterationTimers);
 
     selectServers(
       this,
@@ -848,10 +841,11 @@ function selectServers(topology, selector, timeout, start, callback) {
     }, timeout - duration);
 
     const connectHandler = () => {
-      clearTimeout(failToConnectTimer);
+      clearAndRemoveTimerFrom(failToConnectTimer, topology.s.connectionTimers);
       selectServers(topology, selector, timeout, process.hrtime(), callback);
     };
 
+    topology.s.connectionTimers.add(failToConnectTimer);
     topology.once('connect', connectHandler);
     return;
   }
@@ -884,8 +878,7 @@ function selectServers(topology, selector, timeout, start, callback) {
 
   const retrySelection = () => {
     // clear all existing monitor timers
-    topology.s.monitorTimers.map(timer => clearTimeout(timer));
-    topology.s.monitorTimers = [];
+    drainTimerQueue(topology.s.monitorTimers);
 
     // ensure all server monitors attempt monitoring soon
     topology.s.servers.forEach(server => {
@@ -894,7 +887,7 @@ function selectServers(topology, selector, timeout, start, callback) {
         TOPOLOGY_DEFAULTS.minHeartbeatFrequencyMS
       );
 
-      topology.s.monitorTimers.push(timer);
+      topology.s.monitorTimers.add(timer);
     });
 
     const iterationTimer = setTimeout(() => {
@@ -909,15 +902,14 @@ function selectServers(topology, selector, timeout, start, callback) {
 
     const descriptionChangedHandler = () => {
       // successful iteration, clear the check timer
-      removeTimerFrom(iterationTimer, topology.s.iterationTimers);
-      clearTimeout(iterationTimer);
+      clearAndRemoveTimerFrom(iterationTimer, topology.s.iterationTimers);
 
       // topology description has changed due to monitoring, reattempt server selection
       selectServers(topology, selector, timeout, start, callback);
     };
 
     // track this timer in case we need to clean it up outside this loop
-    topology.s.iterationTimers.push(iterationTimer);
+    topology.s.iterationTimers.add(iterationTimer);
 
     topology.once('topologyDescriptionChanged', descriptionChangedHandler);
   };
@@ -940,11 +932,11 @@ function createAndConnectServer(topology, serverDescription, connectDelay) {
 
   if (connectDelay) {
     const connectTimer = setTimeout(() => {
-      removeTimerFrom(connectTimer, topology.s.connectionTimers);
+      clearAndRemoveTimerFrom(connectTimer, topology.s.connectionTimers);
       server.connect();
     }, connectDelay);
 
-    topology.s.connectionTimers.push(connectTimer);
+    topology.s.connectionTimers.add(connectTimer);
     return server;
   }
 
@@ -971,9 +963,14 @@ function resetServer(topology, serverDescription) {
   topology.s.servers.set(serverDescription.address, newServer);
 }
 
-function removeTimerFrom(timer, timers) {
-  const idx = timers.findIndex(t => t === timer);
-  timers.splice(idx, 1);
+function drainTimerQueue(queue) {
+  queue.forEach(clearTimeout);
+  queue.clear();
+}
+
+function clearAndRemoveTimerFrom(timer, timers) {
+  clearTimeout(timer);
+  return timers.delete(timer);
 }
 
 /**