I noticed that under certain circumstances Progress.fractionCompleted exceeds 1.0 or even resets back to 0. I first noticed it while using the MultipeerConnectivity framework, where I built a progress tree with Progress instances returned from MCSession.sendResource.
The code below reproduces the strange behavior. Simply copy paste.
let childUnitCounts: [(initialCompletedUnitCount: Int64, totalUnitCount: Int64)] = [
(9855, 34375),
(10950, 19110),
(9855, 37511),
(9855, 18799),
(9855, 42705),
(10950, 19021), // When commenting out this line or setting the initial unit count to 0, things work as expected.
]
let parent = Progress(totalUnitCount: Int64(childUnitCounts.count))
let children: [Progress] = childUnitCounts.map { unitCount in
let child = Progress(totalUnitCount: unitCount.totalUnitCount)
child.completedUnitCount = unitCount.initialCompletedUnitCount
parent.addChild(child, withPendingUnitCount: 1)
return child
}
print(parent)
for (i, state) in childUnitCounts.enumerated() {
children[i].completedUnitCount = state.totalUnitCount
print(parent)
}
The above produces the following output:
<NSProgress: 0x600000f6da40> : Parent: 0x0 (portion: 0) / Fraction completed: 0.4088 / Completed: 0 of 6
<NSProgress: 0x600000f6dc20> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2627 / Completed: 9855 of 37511
<NSProgress: 0x600000f6db80> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5730 / Completed: 10950 of 19110
<NSProgress: 0x600000f6dae0> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2867 / Completed: 9855 of 34375
<NSProgress: 0x600000f6de00> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5757 / Completed: 10950 of 19021
<NSProgress: 0x600000f6dd60> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2308 / Completed: 9855 of 42705
<NSProgress: 0x600000f6dcc0> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5242 / Completed: 9855 of 18799
<NSProgress: 0x600000f6da40> : Parent: 0x0 (portion: 0) / Fraction completed: 0.5277 / Completed: 1 of 6
<NSProgress: 0x600000f6dc20> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2627 / Completed: 9855 of 37511
<NSProgress: 0x600000f6db80> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5730 / Completed: 10950 of 19110
<NSProgress: 0x600000f6de00> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5757 / Completed: 10950 of 19021
<NSProgress: 0x600000f6dd60> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2308 / Completed: 9855 of 42705
<NSProgress: 0x600000f6dcc0> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5242 / Completed: 9855 of 18799
<NSProgress: 0x600000f6da40> : Parent: 0x0 (portion: 0) / Fraction completed: 0.5989 / Completed: 2 of 6
<NSProgress: 0x600000f6dc20> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2627 / Completed: 9855 of 37511
<NSProgress: 0x600000f6de00> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5757 / Completed: 10950 of 19021
<NSProgress: 0x600000f6dd60> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2308 / Completed: 9855 of 42705
<NSProgress: 0x600000f6dcc0> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5242 / Completed: 9855 of 18799
<NSProgress: 0x600000f6da40> : Parent: 0x0 (portion: 0) / Fraction completed: 0.8094 / Completed: 3 of 6
<NSProgress: 0x600000f6de00> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5757 / Completed: 10950 of 19021
<NSProgress: 0x600000f6dd60> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2308 / Completed: 9855 of 42705
<NSProgress: 0x600000f6dcc0> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5242 / Completed: 9855 of 18799
<NSProgress: 0x600000f6da40> : Parent: 0x0 (portion: 0) / Fraction completed: 0.8886 / Completed: 4 of 6
<NSProgress: 0x600000f6de00> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5757 / Completed: 10950 of 19021
<NSProgress: 0x600000f6dd60> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.2308 / Completed: 9855 of 42705
<NSProgress: 0x600000f6da40> : Parent: 0x0 (portion: 0) / Fraction completed: 1.0169 / Completed: 5 of 6
<NSProgress: 0x600000f6de00> : Parent: 0x600000f6da40 (portion: 1) / Fraction completed: 0.5757 / Completed: 10950 of 19021
<NSProgress: 0x600000f6da40> : Parent: 0x0 (portion: 0) / Fraction completed: 1.2795 / Completed: 6 of 6
The last line should obviously end with Fraction completed: 1.0. When commenting out the last element of childUnitCounts or setting the initial unit count to 0, it works properly.
I think this is a bug but before reporting it as such, I want to make sure I'm not missing something.
In an attempt to remove sources of doubt, I've gone through various exercises such as adding a delay before each change in a child progress, twiddling various numbers, and even translating the whole thing into Objective-C to make sure this isn't some sort of Swift numerics issue:
int64_t totals[] = {34375, 19110, 37511, 18799, 42705, 19021};
int64_t initials[] = {9855, 10950, 9855, 9855, 9855, 10950};
int sz = 6;
NSProgress* parent = [NSProgress progressWithTotalUnitCount:sz];
NSMutableArray* children = [NSMutableArray array];
for (int i = 0; i<sz; i++) {
NSProgress* child = [NSProgress progressWithTotalUnitCount:totals[i]];
child.completedUnitCount = initials[i];
[children addObject:child];
[parent addChild:child withPendingUnitCount:1];
}
for (int i = 0; i<sz; i++) {
NSProgress* child = children[i];
child.completedUnitCount = totals[i];
}
NSLog(@"%@", parent);
My conclusions are:
Even in Objective-C, the above code ends up with a parent fraction completed of 1.2795.
If sz is 5 or less, the parent fraction completed ends up as 1. The issue seems to arise only when the child count rises above a certain number.
Changing the timing by adding a delay makes no difference (code not shown here).
The very same code run on iOS 12 always gets a parent fraction completed of 1!
So while it takes a great deal to persuade me that Apple could have made such a mistake, I am persuaded. You've found a really nasty bug in iOS 13 Foundation.