fix(Subscription): fold ChildSubscription logic into Subscriber to prevent operators from leaking ChildSubscriptions.

The addition of ChildSubscription to fix #2244 accidentally introduced a different memory leak. Most operators that add and remove inner Subscriptions store the inner Subscriber instance, not the value returned by Subscription#add. When they try to remove the inner Subscription manually, nothing is removed, because the ChildSubscription wrapper instance is the one added to the subscriptions list.

Fixes #2355

Author: trxcllnt

spec/operators/observeOn-spec.ts

@@ -104,21 +104,21 @@ describe('Observable.prototype.observeOn', () => {
       .observeOn(Rx.Scheduler.asap)
       .subscribe(
         x => {
-          const observeOnSubscriber = subscription._subscriptions[0]._innerSub;
+          const observeOnSubscriber = subscription._subscriptions[0];
           expect(observeOnSubscriber._subscriptions.length).to.equal(2); // 1 for the consumer, and one for the notification
-          expect(observeOnSubscriber._subscriptions[1]._innerSub.state.notification.kind)
+          expect(observeOnSubscriber._subscriptions[1].state.notification.kind)
             .to.equal('N');
-          expect(observeOnSubscriber._subscriptions[1]._innerSub.state.notification.value)
+          expect(observeOnSubscriber._subscriptions[1].state.notification.value)
             .to.equal(x);
           results.push(x);
         },
         err => done(err),
         () => {
           // now that the last nexted value is done, there should only be a complete notification scheduled
-          const observeOnSubscriber = subscription._subscriptions[0]._innerSub;
+          const observeOnSubscriber = subscription._subscriptions[0];
           expect(observeOnSubscriber._subscriptions.length).to.equal(2); // 1 for the consumer, one for the complete notification
           // only this completion notification should remain.
-          expect(observeOnSubscriber._subscriptions[1]._innerSub.state.notification.kind)
+          expect(observeOnSubscriber._subscriptions[1].state.notification.kind)
             .to.equal('C');
           // After completion, the entire _subscriptions list is nulled out anyhow, so we can't test much further than this.
           expect(results).to.deep.equal([1, 2, 3]);

spec/operators/switch-spec.ts

@@ -223,4 +223,44 @@ describe('Observable.prototype.switch', () => {
 
     expect(completed).to.be.true;
   });
-});
+
+  it('should not leak when child completes before each switch (prevent memory leaks #2355)', () => {
+    let iStream: Rx.Subject<number>;
+    const oStreamControl = new Rx.Subject<number>();
+    const oStream = oStreamControl.map(() => {
+      return (iStream = new Rx.Subject());
+    });
+    const switcher = oStream.switch();
+    const result = [];
+    let sub = switcher.subscribe((x: number) => result.push(x));
+
+    [0, 1, 2, 3, 4].forEach((n) => {
+      oStreamControl.next(n); // creates inner
+      iStream.complete();
+    });
+    // Expect one child of switch(): The oStream
+    expect(
+      (<any>sub)._subscriptions[0]._subscriptions.length
+    ).to.equal(1);
+    sub.unsubscribe();
+  });
+
+  it('should not leak if we switch before child completes (prevent memory leaks #2355)', () => {
+    const oStreamControl = new Rx.Subject<number>();
+    const oStream = oStreamControl.map(() => {
+      return (new Rx.Subject());
+    });
+    const switcher = oStream.switch();
+    const result = [];
+    let sub = switcher.subscribe((x: number) => result.push(x));
+
+    [0, 1, 2, 3, 4].forEach((n) => {
+      oStreamControl.next(n); // creates inner
+    });
+    // Expect two children of switch(): The oStream and the first inner
+    expect(
+      (<any>sub)._subscriptions[0]._subscriptions.length
+    ).to.equal(2);
+    sub.unsubscribe();
+  });
+});

src/Subscriber.ts

@@ -144,6 +144,18 @@ export class Subscriber<T> extends Subscription implements Observer<T> {
     this.destination.complete();
     this.unsubscribe();
   }
+
+  protected _unsubscribeAndRecycle(): Subscriber<T> {
+    const { _parent, _parents } = this;
+    this._parent = null;
+    this._parents = null;
+    this.unsubscribe();
+    this.closed = false;
+    this.isStopped = false;
+    this._parent = _parent;
+    this._parents = _parents;
+    return this;
+  }
 }
 
 /**
@@ -155,7 +167,7 @@ class SafeSubscriber<T> extends Subscriber<T> {
 
   private _context: any;
 
-  constructor(private _parent: Subscriber<T>,
+  constructor(private _parentSubscriber: Subscriber<T>,
               observerOrNext?: PartialObserver<T> | ((value: T) => void),
               error?: (e?: any) => void,
               complete?: () => void) {
@@ -185,46 +197,46 @@ class SafeSubscriber<T> extends Subscriber<T> {
 
   next(value?: T): void {
     if (!this.isStopped && this._next) {
-      const { _parent } = this;
-      if (!_parent.syncErrorThrowable) {
+      const { _parentSubscriber } = this;
+      if (!_parentSubscriber.syncErrorThrowable) {
         this.__tryOrUnsub(this._next, value);
-      } else if (this.__tryOrSetError(_parent, this._next, value)) {
+      } else if (this.__tryOrSetError(_parentSubscriber, this._next, value)) {
         this.unsubscribe();
       }
     }
   }
 
   error(err?: any): void {
     if (!this.isStopped) {
-      const { _parent } = this;
+      const { _parentSubscriber } = this;
       if (this._error) {
-        if (!_parent.syncErrorThrowable) {
+        if (!_parentSubscriber.syncErrorThrowable) {
           this.__tryOrUnsub(this._error, err);
           this.unsubscribe();
         } else {
-          this.__tryOrSetError(_parent, this._error, err);
+          this.__tryOrSetError(_parentSubscriber, this._error, err);
           this.unsubscribe();
         }
-      } else if (!_parent.syncErrorThrowable) {
+      } else if (!_parentSubscriber.syncErrorThrowable) {
         this.unsubscribe();
         throw err;
       } else {
-        _parent.syncErrorValue = err;
-        _parent.syncErrorThrown = true;
+        _parentSubscriber.syncErrorValue = err;
+        _parentSubscriber.syncErrorThrown = true;
         this.unsubscribe();
       }
     }
   }
 
   complete(): void {
     if (!this.isStopped) {
-      const { _parent } = this;
+      const { _parentSubscriber } = this;
       if (this._complete) {
-        if (!_parent.syncErrorThrowable) {
+        if (!_parentSubscriber.syncErrorThrowable) {
           this.__tryOrUnsub(this._complete);
           this.unsubscribe();
         } else {
-          this.__tryOrSetError(_parent, this._complete);
+          this.__tryOrSetError(_parentSubscriber, this._complete);
           this.unsubscribe();
         }
       } else {
@@ -254,9 +266,9 @@ class SafeSubscriber<T> extends Subscriber<T> {
   }
 
   protected _unsubscribe(): void {
-    const { _parent } = this;
+    const { _parentSubscriber } = this;
     this._context = null;
-    this._parent = null;
-    _parent.unsubscribe();
+    this._parentSubscriber = null;
+    _parentSubscriber.unsubscribe();
   }
 }

src/Subscription.ts

@@ -1,4 +1,3 @@
-import { isArray } from './util/isArray';
 import { isObject } from './util/isObject';
 import { isFunction } from './util/isFunction';
 import { tryCatch } from './util/tryCatch';
@@ -40,7 +39,9 @@ export class Subscription implements ISubscription {
    */
   public closed: boolean = false;
 
-  private _subscriptions: ISubscription[];
+  protected _parent: Subscription = null;
+  protected _parents: Subscription[] = null;
+  private _subscriptions: ISubscription[] = null;
 
   /**
    * @param {function(): void} [unsubscribe] A function describing how to
@@ -66,11 +67,25 @@ export class Subscription implements ISubscription {
       return;
     }
 
-    this.closed = true;
-
-    const { _unsubscribe, _subscriptions } = (<any> this);
+    let { _parent, _parents, _unsubscribe, _subscriptions } = (<any> this);
 
-    (<any> this)._subscriptions = null;
+    this.closed = true;
+    this._parent = null;
+    this._parents = null;
+    // null out _subscriptions first so any child subscriptions that attempt
+    // to remove themselves from this subscription will noop
+    this._subscriptions = null;
+
+    let index = -1, len = _parents && _parents.length || 0;
+
+    // if this._parent is null, then so is this._parents, and we
+    // don't have to remove ourselves from any parent subscriptions.
+    while (_parent) {
+      _parent.remove(this);
+      // if this._parents is null or index >= len,
+      // then _parent is set to false, and the loop exits
+      _parent = ++index < len && _parents[index];
+    }
 
     if (isFunction(_unsubscribe)) {
       let trial = tryCatch(_unsubscribe).call(this);
@@ -83,10 +98,10 @@ export class Subscription implements ISubscription {
       }
     }
 
-    if (isArray(_subscriptions)) {
+    if (_subscriptions) {
 
-      let index = -1;
-      const len = _subscriptions.length;
+      index = -1;
+      len = _subscriptions.length;
 
       while (++index < len) {
         const sub = _subscriptions[index];
@@ -138,27 +153,33 @@ export class Subscription implements ISubscription {
       return this;
     }
 
-    let sub = (<Subscription> teardown);
+    let subscription = (<Subscription> teardown);
 
     switch (typeof teardown) {
       case 'function':
-        sub = new Subscription(<(() => void) > teardown);
+        subscription = new Subscription(<(() => void) > teardown);
       case 'object':
-        if (sub.closed || typeof sub.unsubscribe !== 'function') {
-          return sub;
+        if (subscription.closed || typeof subscription.unsubscribe !== 'function') {
+          return subscription;
         } else if (this.closed) {
-          sub.unsubscribe();
-          return sub;
+          subscription.unsubscribe();
+          return subscription;
+        } else if (typeof subscription._addParent !== 'function' /* quack quack */) {
+          const tmp = subscription;
+          subscription = new Subscription();
+          subscription._subscriptions = [tmp];
         }
         break;
       default:
         throw new Error('unrecognized teardown ' + teardown + ' added to Subscription.');
     }
 
-    const childSub = new ChildSubscription(sub, this);
-    this._subscriptions = this._subscriptions || [];
-    this._subscriptions.push(childSub);
-    return childSub;
+    const subscriptions = this._subscriptions || (this._subscriptions = []);
+
+    subscriptions.push(subscription);
+    subscription._addParent(this);
+
+    return subscription;
   }
 
   /**
@@ -168,37 +189,25 @@ export class Subscription implements ISubscription {
    * @return {void}
    */
   remove(subscription: Subscription): void {
-
-    // HACK: This might be redundant because of the logic in `add()`
-    if (subscription == null   || (
-        subscription === this) || (
-        subscription === Subscription.EMPTY)) {
-      return;
-    }
-
-    const subscriptions = (<any> this)._subscriptions;
-
+    const subscriptions = this._subscriptions;
     if (subscriptions) {
       const subscriptionIndex = subscriptions.indexOf(subscription);
       if (subscriptionIndex !== -1) {
         subscriptions.splice(subscriptionIndex, 1);
       }
     }
   }
-}
-
-export class ChildSubscription extends Subscription {
-  constructor(private _innerSub: ISubscription, private _parent: Subscription) {
-    super();
-  }
 
-  _unsubscribe() {
-    const { _innerSub, _parent } = this;
-    _parent.remove(this);
-    _innerSub.unsubscribe();
+  private _addParent(parent: Subscription) {
+    let { _parent, _parents } = this;
+    if (!_parent) {
+      this._parent = parent;
+    } else if (_parents || (_parents = this._parents = [])) {
+      _parents.push(this);
+    }
   }
 }
 
 function flattenUnsubscriptionErrors(errors: any[]) {
  return errors.reduce((errs, err) => errs.concat((err instanceof UnsubscriptionError) ? err.errors : err), []);
-}
+}

src/operator/catch.ts

@@ -107,9 +107,7 @@ class CatchSubscriber<T, R> extends OuterSubscriber<T, R> {
         super.error(err2);
         return;
       }
-      this.unsubscribe();
-      this.closed = false;
-      this.isStopped = false;
+      this._unsubscribeAndRecycle();
       this.add(subscribeToResult(this, result));
     }
   }

src/operator/observeOn.ts

@@ -4,7 +4,7 @@ import { Operator } from '../Operator';
 import { PartialObserver } from '../Observer';
 import { Subscriber } from '../Subscriber';
 import { Notification } from '../Notification';
-import { TeardownLogic, Subscription } from '../Subscription';
+import { TeardownLogic } from '../Subscription';
 import { Action } from '../scheduler/Action';
 
 /**
@@ -36,11 +36,9 @@ export class ObserveOnOperator<T> implements Operator<T, T> {
  */
 export class ObserveOnSubscriber<T> extends Subscriber<T> {
   static dispatch(this: Action<ObserveOnMessage>, arg: ObserveOnMessage) {
-    const { notification, destination, subscription } = arg;
+    const { notification, destination } = arg;
     notification.observe(destination);
-    if (subscription) {
-      subscription.unsubscribe();
-    }
+    this.unsubscribe();
   }
 
   constructor(destination: Subscriber<T>,
@@ -50,10 +48,11 @@ export class ObserveOnSubscriber<T> extends Subscriber<T> {
   }
 
   private scheduleMessage(notification: Notification<any>): void {
-    const message = new ObserveOnMessage(notification, this.destination);
-    message.subscription = this.add(
-        this.scheduler.schedule(ObserveOnSubscriber.dispatch, this.delay, message)
-    );
+    this.add(this.scheduler.schedule(
+      ObserveOnSubscriber.dispatch,
+      this.delay,
+      new ObserveOnMessage(notification, this.destination)
+    ));
   }
 
   protected _next(value: T): void {
@@ -70,8 +69,6 @@ export class ObserveOnSubscriber<T> extends Subscriber<T> {
 }
 
 export class ObserveOnMessage {
-  public subscription: Subscription;
-
   constructor(public notification: Notification<any>,
               public destination: PartialObserver<any>) {
   }

src/operator/repeat.ts

@@ -56,10 +56,7 @@ class RepeatSubscriber<T> extends Subscriber<T> {
       } else if (count > -1) {
         this.count = count - 1;
       }
-      this.unsubscribe();
-      this.isStopped = false;
-      this.closed = false;
-      source.subscribe(this);
+      source.subscribe(this._unsubscribeAndRecycle());
     }
   }
 }