Bug Report

Current Behavior
When instantiating a Subscription and passing a callback, that callback is saved asthis._unsubscribe of theSubscription object:

When unsubscribing that Subscription, the function is called, but not nulled out afterwards:

This means that if it did some manual resource cleanup like closing a MessagePort, that MessagePort still can't be garbage-collected, because the callback, and therefor the Subscription, still holds a reference to it.

This is different from Subscriptions added viaadd(), which are correctly de-referenced:

Reproduction

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const{ port1}=newMessageChannel()constsubscription=newSubscription(()=>{port1.close()})subscription.unsubscribe()console.log(subscription._unsubscribe)

Expected behavior
After calling the callback,this._unsubscribe should be nulled out so the callback and its references can be garbage-collected. Since a Subscription can only be unsubscribed once, there is no need to keep the reference.

Environment

• Runtime: All
• RxJS version: 6.5.5

Possible Solution
Setthis._unsubscribe tonull whenunsubscribe() is called.