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Fixed in 5.5.0

Votes

4

Found in

5.3.5f1

Issue ID

810451

Regression

No

[Android][iOS] Thread.MemoryBarrier() does not prevent instruction reordering with mono backend

Scripting

-

Reproduction steps
--------------------------
1) Open attached project "MemoryBarrierRepro"
2) Build scene "testScene" for Android/iOS
3) Run on a device
4) Observe the log
--- You will see results of user's test in this format: "wrong value 42323173 ,correct: 42323177 ,previous: 42323176"

Comments (2)

  1. 1d8146644242011147550519dfc46b8b?d=mm

    Douvantzis

    Jul 07, 2016 22:43

    A similar bug has been filed for Mono 4. However in Mono 4 the test does not fail when Memory Barriers are used. The bug in that case is reproduced when a Volatile field is used instead of Memory Barrier.

    You can read the discussion here:
    http://mono.1490590.n4.nabble.com/Volatile-fields-don-t-enforce-acquire-release-semantics-like-Volatile-Read-and-Volatile-Write-td4668111.html

  2. 1d8146644242011147550519dfc46b8b?d=mm

    Douvantzis

    Jul 06, 2016 09:46

    Volatile fields have also a related problem in Unity' Mono run time for Android and iOS. They don't have acquire and release semantics: https://msdn.microsoft.com/en-us/library/aa645755.aspx

    It's as if no memory fences are applied.

    The submitted test project fails if instead of using MemoryBarriers, a volatile field is used.

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