Promises are registered upon entry to the pool and unregistered upon exit. If all promises are in a 'pending' state, new promises can't be processed. Upon completion of a registered promise, it is unregistered, allowing space for a new promise. The code path responsible for unregistering promises when they resolve runs each time a promise's callback is called. Unfortunately, there's no guarantee that the callback will be invoked upon the promise's resolution. For instance, promises registered with only a 'catch' callback may never be triggered when the promise resolves correctly. This commit ensures that a final callback is always registered, even if the user did not provide one. This guarantees that promises are always unregistered upon resolution Fixes: QTBUG-118161 Pick-to: 6.5 6.6 6.7 Change-Id: Ifea93d692464a6ef40c4bcad60f840ca0cb650c9 Reviewed-by: Lorn Potter <lorn.potter@gmail.com>