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Avoid large exponents in BackoffMachine #1339

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PIG208 opened this issue Feb 7, 2025 · 2 comments · May be fixed by #1352
Open

Avoid large exponents in BackoffMachine #1339

PIG208 opened this issue Feb 7, 2025 · 2 comments · May be fixed by #1352
Labels
a-api Implementing specific parts of the Zulip server API a-sync Event queue; retry; local echo; races
Milestone
M6: Post-launch

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@PIG208
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PIG208 commented Feb 7, 2025 

  Future<void> wait() async {
    final bound = _minDuration(maxBound,
                               firstBound * pow(base, _waitsCompleted));
[ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: Unsupported operation: Infinity or NaN toInt
#0      double.round (dart:core-patch/double.dart)
#1      Duration.* (dart:core/duration.dart:213:56)
#2      BackoffMachine.wait (package:zulip/api/backoff.dart:87:43)
#3      UpdateMachine._registerQueueWithRetry (package:zulip/model/store.dart:930:53)
<asynchronous suspension>
#4      UpdateMachine.load (package:zulip/model/store.dart:875:29)
<asynchronous suspension>
#5      LiveGlobalStore.doLoadPerAccount (package:zulip/model/store.dart:816:27)

What might have happened here is that _waitsCompleted gets to a large enough value that pow(base, _waitsCompleted) becomes either infinity or NaN.

Proposed fix by Greg:

  • Instead of only _waitsCompleted, have also a (private) field equivalent to that bound local.
  • Then at each iteration, multiply that by base and apply _minDuration.
  • That way there's no pow (especially none with a potentially-large argument), and no giant numbers as intermediates in the calculation.

CZO discussion
@PIG208 PIG208 added a-api Implementing specific parts of the Zulip server API a-sync Event queue; retry; local echo; races labels Feb 7, 2025
@PIG208 PIG208 added this to the M6: Post-launch milestone Feb 7, 2025
@ajayrajsaini
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hi @PIG208,
i will love contribute to this issue, if it is still open

@suraj-aayush
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suraj-aayush commented Feb 13, 2025 •
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Hi @PIG208
I would like to work on this issue. Can you please assign it to me?
I have set up and corrected the code.

My Code:
Fixes incorrect backoff logic – Now, _currentBound correctly increases exponentially.
Prevents exceeding maxBound – Ensures we don’t wait longer than necessary.
Improves reliability – Makes sure backoff logic works consistently across retries.

@PIG208 PIG208 linked a pull request Feb 14, 2025 that will close this issue
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Labels
a-api Implementing specific parts of the Zulip server API a-sync Event queue; retry; local echo; races
Projects
Flutter app
Status: No status
Milestone
M6: Post-launch
3 participants
@PIG208 @suraj-aayush @ajayrajsaini