fix(core): Multiple subscribers to ApplicationRef.isStable should all see values (#53541)

atscott · alxhub · commit c16b5e82901b · 2023-12-13T11:26:52.000-08:00
The behavior of `ApplicationRef.isStable` changed in 16.1 due to 28c68f7. This change added a `share` to the `isStable` observable, which prevents additional subscribers from getting a value until a new one emits. One solution to the problem would be `shareReplay(1)`. However, that would increase the bundle size since we do not use `shareReplay` elsewhere. Instead, we don't even really need to share the observable. The `Observable` available in `ApplicationRef.isStable` before the above commit was the zone stable observable, without a `share`. The new behavior adds only an additional observable to the stream, `hasPendingTasks` (a `BehaviorSubject`). The observables in this stream are not expensive to subscribe to. The only one with side effects is the `isStable` (because it subscribes to onStable), but that one already has the `share` operator on it. Omitting the `share` in `ApplicationRef` also means that applications on `zoneless` will not have to pay the cost of the operator when we make zones optional because the zone stable observable is the only place we use it. PR Close #53541
diff --git a/packages/core/src/application/application_ref.ts b/packages/core/src/application/application_ref.ts
@@ -10,7 +10,7 @@ import '../util/ng_jit_mode';
 
 import {setThrowInvalidWriteToSignalError} from '@angular/core/primitives/signals';
 import {Observable, of} from 'rxjs';
-import {distinctUntilChanged, first, share, switchMap} from 'rxjs/operators';
+import {distinctUntilChanged, first, switchMap} from 'rxjs/operators';
 
 import {getCompilerFacade, JitCompilerUsage} from '../compiler/compiler_facade';
 import {Console} from '../console';
@@ -351,7 +351,6 @@ export class ApplicationRef {
           .hasPendingTasks.pipe(
               switchMap(hasPendingTasks => hasPendingTasks ? of(false) : this.zoneIsStable),
               distinctUntilChanged(),
-              share(),
           );
 
   private readonly _injector = inject(EnvironmentInjector);
diff --git a/packages/core/test/application_ref_spec.ts b/packages/core/test/application_ref_spec.ts
@@ -21,6 +21,7 @@ import type {ServerModule} from '@angular/platform-server';
 import {ApplicationRef} from '../src/application/application_ref';
 import {NoopNgZone} from '../src/zone/ng_zone';
 import {ComponentFixtureNoNgZone, inject, TestBed, waitForAsync, withModule} from '../testing';
+import {take} from 'rxjs/operators';
 
 let serverPlatformModule: Promise<Type<ServerModule>>|null = null;
 if (isNode) {
@@ -795,6 +796,14 @@ describe('AppRef', () => {
        expectStableTexts(MacroMicroTaskComp, ['111']);
      }));
 
+  it('isStable can be subscribed to many times', async () => {
+    const appRef: ApplicationRef = TestBed.inject(ApplicationRef);
+    // Create stable subscription but do not unsubscribe before the second subscription is made
+    appRef.isStable.subscribe();
+    await expectAsync(appRef.isStable.pipe(take(1)).toPromise()).toBeResolved();
+    stableCalled = true;
+  });
+
   describe('unstable', () => {
     let unstableCalled = false;
 
diff --git a/packages/core/test/bundling/animations-standalone/bundle.golden_symbols.json b/packages/core/test/bundling/animations-standalone/bundle.golden_symbols.json
@@ -1406,9 +1406,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/animations/bundle.golden_symbols.json b/packages/core/test/bundling/animations/bundle.golden_symbols.json
@@ -1478,9 +1478,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/cyclic_import/bundle.golden_symbols.json b/packages/core/test/bundling/cyclic_import/bundle.golden_symbols.json
@@ -1178,9 +1178,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/defer/bundle.golden_symbols.json b/packages/core/test/bundling/defer/bundle.golden_symbols.json
@@ -2336,9 +2336,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/forms_reactive/bundle.golden_symbols.json b/packages/core/test/bundling/forms_reactive/bundle.golden_symbols.json
@@ -1649,9 +1649,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/forms_template_driven/bundle.golden_symbols.json b/packages/core/test/bundling/forms_template_driven/bundle.golden_symbols.json
@@ -1625,9 +1625,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/hello_world/bundle.golden_symbols.json b/packages/core/test/bundling/hello_world/bundle.golden_symbols.json
@@ -932,9 +932,6 @@
   {
     "name": "setUpAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/hydration/bundle.golden_symbols.json b/packages/core/test/bundling/hydration/bundle.golden_symbols.json
@@ -1274,9 +1274,6 @@
   {
     "name": "setUpAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/router/bundle.golden_symbols.json b/packages/core/test/bundling/router/bundle.golden_symbols.json
@@ -1961,9 +1961,6 @@
   {
     "name": "shallowEqual"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/standalone_bootstrap/bundle.golden_symbols.json b/packages/core/test/bundling/standalone_bootstrap/bundle.golden_symbols.json
@@ -1031,9 +1031,6 @@
   {
     "name": "setUpAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },
diff --git a/packages/core/test/bundling/todo/bundle.golden_symbols.json b/packages/core/test/bundling/todo/bundle.golden_symbols.json
@@ -1418,9 +1418,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

Original file line number	Diff line number	Diff line change
`@@ -1406,9 +1406,6 @@`
`1406`	`1406`	`{`
`1407`	`1407`	`"name": "setupStaticAttributes"`
`1408`	`1408`	`},`
`1409`		`- {`
`1410`		`- "name": "share"`
`1411`		`- },`
`1412`	`1409`	`{`
`1413`	`1410`	`"name": "shareSubjectFactory"`
`1414`	`1411`	`},`
Original file line number	Diff line number	Diff line change
`@@ -1478,9 +1478,6 @@`
`1478`	`1478`	`{`
`1479`	`1479`	`"name": "setupStaticAttributes"`
`1480`	`1480`	`},`
`1481`		`- {`
`1482`		`- "name": "share"`
`1483`		`- },`
`1484`	`1481`	`{`
`1485`	`1482`	`"name": "shareSubjectFactory"`
`1486`	`1483`	`},`
Original file line number	Diff line number	Diff line change
`@@ -1178,9 +1178,6 @@`
`1178`	`1178`	`{`
`1179`	`1179`	`"name": "setupStaticAttributes"`
`1180`	`1180`	`},`
`1181`		`- {`
`1182`		`- "name": "share"`
`1183`		`- },`
`1184`	`1181`	`{`
`1185`	`1182`	`"name": "shareSubjectFactory"`
`1186`	`1183`	`},`
Original file line number	Diff line number	Diff line change
`@@ -2336,9 +2336,6 @@`
`2336`	`2336`	`{`
`2337`	`2337`	`"name": "setupStaticAttributes"`
`2338`	`2338`	`},`
`2339`		`- {`
`2340`		`- "name": "share"`
`2341`		`- },`
`2342`	`2339`	`{`
`2343`	`2340`	`"name": "shareSubjectFactory"`
`2344`	`2341`	`},`
Original file line number	Diff line number	Diff line change
`@@ -1649,9 +1649,6 @@`
`1649`	`1649`	`{`
`1650`	`1650`	`"name": "setupStaticAttributes"`
`1651`	`1651`	`},`
`1652`		`- {`
`1653`		`- "name": "share"`
`1654`		`- },`
`1655`	`1652`	`{`
`1656`	`1653`	`"name": "shareSubjectFactory"`
`1657`	`1654`	`},`
Original file line number	Diff line number	Diff line change
`@@ -1625,9 +1625,6 @@`
`1625`	`1625`	`{`
`1626`	`1626`	`"name": "setupStaticAttributes"`
`1627`	`1627`	`},`
`1628`		`- {`
`1629`		`- "name": "share"`
`1630`		`- },`
`1631`	`1628`	`{`
`1632`	`1629`	`"name": "shareSubjectFactory"`
`1633`	`1630`	`},`
Original file line number	Diff line number	Diff line change
`@@ -932,9 +932,6 @@`
`932`	`932`	`{`
`933`	`933`	`"name": "setUpAttributes"`
`934`	`934`	`},`
`935`		`- {`
`936`		`- "name": "share"`
`937`		`- },`
`938`	`935`	`{`
`939`	`936`	`"name": "shareSubjectFactory"`
`940`	`937`	`},`
Original file line number	Diff line number	Diff line change
`@@ -1274,9 +1274,6 @@`
`1274`	`1274`	`{`
`1275`	`1275`	`"name": "setUpAttributes"`
`1276`	`1276`	`},`
`1277`		`- {`
`1278`		`- "name": "share"`
`1279`		`- },`
`1280`	`1277`	`{`
`1281`	`1278`	`"name": "shareSubjectFactory"`
`1282`	`1279`	`},`