Don't set up more than 1 abort signal listener (#503)

Author: gustavohenke

src/completion-listener.spec.ts

@@ -1,3 +1,4 @@
+import { getEventListeners, getMaxListeners } from 'events';
 import { TestScheduler } from 'rxjs/testing';
 
 import { CloseEvent } from './command';
@@ -56,6 +57,16 @@ describe('listen', () => {
         await expect(result).resolves.toHaveLength(0);
     });
 
+    it('does not leak memory when listening for abort signals', () => {
+        const abortCtrl = new AbortController();
+        const maxListeners = getMaxListeners(abortCtrl.signal);
+        createController().listen(
+            Array.from({ length: maxListeners + 1 }, () => new FakeCommand()),
+            abortCtrl.signal,
+        );
+        expect(getEventListeners(abortCtrl.signal, 'abort')).toHaveLength(1);
+    });
+
     it('check for success once all commands have emitted at least a single close event', async () => {
         const finallyCallback = jest.fn();
         const result = createController().listen(commands).finally(finallyCallback);

src/completion-listener.ts

@@ -1,5 +1,5 @@
 import * as Rx from 'rxjs';
-import { delay, filter, map, switchMap, take } from 'rxjs/operators';
+import { delay, filter, map, share, switchMap, take } from 'rxjs/operators';
 
 import { CloseEvent, Command } from './command';
 
@@ -101,6 +101,9 @@ export class CompletionListener {
                 // without an immediate delay
                 delay(0, this.scheduler),
                 map(() => undefined),
+                // #502 - node might warn of too many active listeners on this object if it isn't shared,
+                // as each command subscribes to abort event over and over
+                share(),
             );
 
         const closeStreams = commands.map((command) =>