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Fix 68f2213: Don't use GetPoolSize() for end of pool iterator #9461

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merged 1 commit into from Aug 10, 2021

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@glx22 glx22 commented Aug 3, 2021

Motivation / Problem

GetPoolSize() returned value can change during the pool iteration, so using it for end() was not a good idea.

Description

Use a constant (max size of the pool) for end(), and set index to this value whenever it reaches GetPoolSize().

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

  • The bug fix is important enough to be backported? (label: 'backport requested')
  • This PR affects the save game format? (label 'savegame upgrade')
  • This PR affects the GS/AI API? (label 'needs review: Script API')
    • ai_changelog.hpp, gs_changelog.hpp need updating.
    • The compatibility wrappers (compat_*.nut) need updating.
  • This PR affects the NewGRF API? (label 'needs review: NewGRF')
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@rubidium42 rubidium42 left a comment

Might solve #9458, but definitely solves a desync via the Vehicle tick counter creating effect vehicles that might not get iterated over.
This as the range based for loop gets end, i.e the original pool size (or actually the highest ID ever assigned), and iterates up to there. If the game already ran a while that highest ID might be significantly higher than the current highest ID, so a joining client would have a lower highest ID, and thus a lower pool size and thus a lower 'value' for end(). This means that in the existing clients the effect vehicle created in the vehicle tick gets iterated over, whereas it does not in the newly joined client causing a divergence in state and eventual desync. Especially as the effect vehicle will be removed earlier, and all assigned vehicle IDs may be off after that event.

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@glx22 glx22 merged commit 8a083cd into OpenTTD:master Aug 10, 2021
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@glx22 glx22 deleted the pool_iterator branch Aug 10, 2021
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3 participants