refactor(topology): remove extra timers around selection monitoring

Author: mbroadst

lib/core/sdam/server_selection.js

@@ -8,8 +8,6 @@ const MongoTimeoutError = require('../error').MongoTimeoutError;
 
 const common = require('./common');
 const STATE_CLOSED = common.STATE_CLOSED;
-const TOPOLOGY_DEFAULTS = common.TOPOLOGY_DEFAULTS;
-const drainTimerQueue = common.drainTimerQueue;
 const clearAndRemoveTimerFrom = common.clearAndRemoveTimerFrom;
 
 // max staleness constants
@@ -183,7 +181,8 @@ function readPreferenceServerSelector(readPreference) {
     const commonWireVersion = topologyDescription.commonWireVersion;
     if (
       commonWireVersion &&
-      (readPreference.minWireVersion && readPreference.minWireVersion > commonWireVersion)
+      readPreference.minWireVersion &&
+      readPreference.minWireVersion > commonWireVersion
     ) {
       throw new MongoError(
         `Minimum wire version '${
@@ -298,18 +297,10 @@ function selectServers(topology, selector, timeout, start, callback) {
   }
 
   const retrySelection = () => {
-    // clear all existing monitor timers
-    drainTimerQueue(topology.s.monitorTimers);
-
     // ensure all server monitors attempt monitoring soon
-    topology.s.servers.forEach(server => {
-      const timer = setTimeout(
-        () => server.monitor({ heartbeatFrequencyMS: topology.description.heartbeatFrequencyMS }),
-        TOPOLOGY_DEFAULTS.minHeartbeatFrequencyMS
-      );
-
-      topology.s.monitorTimers.add(timer);
-    });
+    topology.s.servers.forEach(server =>
+      server.monitor({ heartbeatFrequencyMS: topology.description.heartbeatFrequencyMS })
+    );
 
     const iterationTimer = setTimeout(() => {
       topology.removeListener('topologyDescriptionChanged', descriptionChangedHandler);

lib/core/sdam/topology.js

@@ -175,7 +175,6 @@ class Topology extends EventEmitter {
       clusterTime: null,
 
       // timer management
-      monitorTimers: new Set(),
       iterationTimers: new Set(),
       connectionTimers: new Set()
     };
@@ -334,7 +333,6 @@ class Topology extends EventEmitter {
     }
 
     // clear all existing monitor timers
-    drainTimerQueue(this.s.monitorTimers);
     drainTimerQueue(this.s.iterationTimers);
     drainTimerQueue(this.s.connectionTimers);