Fix memory leaks in Promise whenAll #1016
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| waitForExpectations(timeout: 1) | ||
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| XCTAssertNil(weakPromise0) | ||
| XCTAssertNil(weakPromise1) |
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So before this fix, this particular assert would fail, correct?
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Actually, all three of the asserts were failing. The notify block references the entire array of promises, so all of them are retained.
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oof, ouch. well this is definitely an improvement.
designatednerd
approved these changes
Feb 13, 2020
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When any of the promises reject, we were calling reject, but never leaving the
DispatchGroup. This means thenotifyblock was never being scheduled. This is what we wanted, but the unintended consequence of that is that thenotifyblock was then retained indefinitely, and thegroup.notifyblock is retaining thepromisesor theresultOrPromises. This way, the notify block gets called and releases it's reference to thepromises, but if any rejects occured, it does not callfulfill.@designatednerd I was seeing memory leaks in my application and was able to track it down to this. I wrote a unit test for
Promise, but unit testing memory leaks of value semantic entities is impossible, so I can't provide a unit test forResultOrPromise. I tested the fix with my app, and the memory leaks are gone now.