Merge pull request #3205 from nasa/data-dropout-fixes

### Reviewer Checklist

1. Changes appear to address issue? Y
2. Appropriate unit tests included? Y
3. Code style and in-line documentation are appropriate? Y
4. Commit messages meet standards? Y
5. Has associated issue been labelled `unverified`? (only applicable if this PR closes the issue) Y

src/api/telemetry/TelemetryAPI.js

@@ -334,8 +334,8 @@ define([
             });
             if (subscriber.callbacks.length === 0) {
                 subscriber.unsubscribe();
+                delete this.subscribeCache[keyString];
             }
-            delete this.subscribeCache[keyString];
         }.bind(this);
     };
 

src/api/telemetry/TelemetryAPISpec.js

@@ -156,6 +156,29 @@ define([
                 expect(callbacktwo).not.toHaveBeenCalledWith('anotherValue');
             });
 
+            it('only deletes subscription cache when there are no more subscribers', function () {
+                var unsubFunc = jasmine.createSpy('unsubscribe');
+                telemetryProvider.subscribe.and.returnValue(unsubFunc);
+                telemetryProvider.supportsSubscribe.and.returnValue(true);
+                telemetryAPI.addProvider(telemetryProvider);
+
+                var callback = jasmine.createSpy('callback');
+                var callbacktwo = jasmine.createSpy('callback two');
+                var callbackThree = jasmine.createSpy('callback three');
+                var unsubscribe = telemetryAPI.subscribe(domainObject, callback);
+                var unsubscribeTwo = telemetryAPI.subscribe(domainObject, callbacktwo);
+
+                expect(telemetryProvider.subscribe.calls.count()).toBe(1);
+                unsubscribe();
+                var unsubscribeThree = telemetryAPI.subscribe(domainObject, callbackThree);
+                // Regression test for where subscription cache was deleted on each unsubscribe, resulting in
+                // superfluous additional subscriptions. If the subscription cache is being deleted on each unsubscribe,
+                // then a subsequent subscribe will result in a new subscription at the provider.
+                expect(telemetryProvider.subscribe.calls.count()).toBe(1);
+                unsubscribeTwo();
+                unsubscribeThree();
+            });
+
             it('does subscribe/unsubscribe', function () {
                 var unsubFunc = jasmine.createSpy('unsubscribe');
                 telemetryProvider.subscribe.and.returnValue(unsubFunc);

src/plugins/condition/StyleRuleManager.js

@@ -46,6 +46,7 @@ export default class StyleRuleManager extends EventEmitter {
         if (this.isEditing) {
             if (this.stopProvidingTelemetry) {
                 this.stopProvidingTelemetry();
+                delete this.stopProvidingTelemetry;
             }
             if (this.conditionSetIdentifier) {
                 this.applySelectedConditionStyle();
@@ -66,6 +67,7 @@ export default class StyleRuleManager extends EventEmitter {
     subscribeToConditionSet() {
         if (this.stopProvidingTelemetry) {
             this.stopProvidingTelemetry();
+            delete this.stopProvidingTelemetry;
         }
         this.openmct.objects.get(this.conditionSetIdentifier).then((conditionSetDomainObject) => {
             this.openmct.telemetry.request(conditionSetDomainObject)
@@ -154,8 +156,8 @@ export default class StyleRuleManager extends EventEmitter {
         this.applyStaticStyle();
         if (this.stopProvidingTelemetry) {
             this.stopProvidingTelemetry();
+            delete this.stopProvidingTelemetry;
         }
-        delete this.stopProvidingTelemetry;
         this.conditionSetIdentifier = undefined;
     }
 

src/plugins/condition/components/inspector/ConditionalStylesView.vue

@@ -197,6 +197,7 @@ export default {
             }
             if (this.stopProvidingTelemetry) {
                 this.stopProvidingTelemetry();
+                delete this.stopProvidingTelemetry;
             }
         },
         initialize(conditionSetDomainObject) {
@@ -210,6 +211,7 @@ export default {
             if (this.isEditing) {
                 if (this.stopProvidingTelemetry) {
                     this.stopProvidingTelemetry();
+                    delete this.stopProvidingTelemetry;
                 }
             } else {
                 this.subscribeToConditionSet();
@@ -307,6 +309,7 @@ export default {
             this.persist(domainObjectStyles);
             if (this.stopProvidingTelemetry) {
                 this.stopProvidingTelemetry();
+                delete this.stopProvidingTelemetry;
             }
         },
         updateDomainObjectItemStyles(newItems) {
@@ -375,6 +378,7 @@ export default {
         subscribeToConditionSet() {
             if (this.stopProvidingTelemetry) {
                 this.stopProvidingTelemetry();
+                delete this.stopProvidingTelemetry;
             }
             if (this.conditionSetDomainObject) {
                 this.openmct.telemetry.request(this.conditionSetDomainObject)

src/plugins/condition/components/inspector/StylesView.vue

@@ -190,6 +190,7 @@ export default {
             if (this.isEditing) {
                 if (this.stopProvidingTelemetry) {
                     this.stopProvidingTelemetry();
+                    delete this.stopProvidingTelemetry;
                 }
             } else {
                 this.subscribeToConditionSet();
@@ -325,6 +326,7 @@ export default {
 
             if (this.stopProvidingTelemetry) {
                 this.stopProvidingTelemetry();
+                delete this.stopProvidingTelemetry;
             }
 
             if (this.unObserveObjects) {
@@ -337,6 +339,7 @@ export default {
         subscribeToConditionSet() {
             if (this.stopProvidingTelemetry) {
                 this.stopProvidingTelemetry();
+                delete this.stopProvidingTelemetry;
             }
             if (this.conditionSetDomainObject) {
                 this.openmct.telemetry.request(this.conditionSetDomainObject)
@@ -494,6 +497,7 @@ export default {
 
             if (this.stopProvidingTelemetry) {
                 this.stopProvidingTelemetry();
+                delete this.stopProvidingTelemetry;
             }
         },
         removeConditionalStyles(domainObjectStyles, itemId) {