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Add NTP synchronization by using Kronos. #54
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,29 @@ | ||
| /* | ||
| * Unless explicitly stated otherwise all files in this repository are licensed under the Apache License Version 2.0. | ||
| * This product includes software developed at Datadog (https://www.datadoghq.com/). | ||
| * Copyright 2020-2021 Datadog, Inc. | ||
| */ | ||
|
|
||
| import Foundation | ||
| @_implementationOnly import Kronos | ||
| @_implementationOnly import OpenTelemetrySdk | ||
|
|
||
| class NTPClock: OpenTelemetrySdk.Clock { | ||
| init() { | ||
| Kronos.Clock.sync() | ||
| } | ||
|
|
||
| var now: Date { | ||
| if Thread.isMainThread { | ||
| return Kronos.Clock.now ?? Date() | ||
| } else { | ||
| var date = Date() | ||
| DispatchQueue.main.sync { | ||
| if let now = Kronos.Clock.now { | ||
| date = now | ||
| } | ||
| } | ||
| return date | ||
| } | ||
| } | ||
| } |
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I don't have enough visibility on how
otel-swiftuses theClock.now, but one thing we had to mitigate indd-sdk-ioswasKronos.Clock.nowbeing not monotonic until.sync()resolves all calls to the NTP pool.In other words, this:
might give negative
deltafor the first attempts when NTP sync is being performed and device time is ahead of the NTP time.When browsing this (start) and this (end) code in
otel-swift, I'm not sure if this is not the case here. Is it?There was a problem hiding this comment.
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otel-swiftuses a monotonic clock for each span, which is initialized with the value of the active clock (Kronos clock in this case) that is only called once per span at the start, so durations should never be negative. But those spans can be started from any thread, so I cannot use theKronos.Clock.nowdirectly, I must evaluate if performance will suffer much from calling it in the main thread since I only call it once per spanThere was a problem hiding this comment.
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I think I will start with the simplest implementation, in my framework most of the spans will start at main thread (XCTest observer), and performance should not be so critical
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It's definitely the easiest solution 👍, will work if you can make this threading assumption. Otherwise, we solved this (in DataDog/dd-sdk-ios#607) by using our
ValuePublisherwhich usesDispatchQueue. This comes with lock penalty, which we mitigate by using concurrent queue with.barrierfor making (rare) writes exclusive and allowing (frequent) simultaneous reads.There was a problem hiding this comment.
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If I find my solution performance is not good enough I will try to change to your solution, its way better than mine.