Condition.wait inside Event is not protected against spurious wakeups

[vicuna]

Original bug ID: 7013
Reporter: aha
Status: closed (set by @xavierleroy on 2017-09-24T15:33:05Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 4.02.3
Target version: 4.03.0+dev / +beta1
Fixed in version: 4.03.0+dev / +beta1
Category: otherlibs
Has duplicate: #7286

Bug description

Condition.wait at Line 87 (

ocaml/otherlibs/systhreads/event.ml

Line 87 in fa457b3

Condition.wait condition masterlock

) is not protected against spurious wakeups. An Invalid_argument-"index out of bounds"-exception is thrown instead (at Line 93 or 96) - not very helpful.
See for example: ocsigen/lwt#186

Steps to reproduce

It's difficult to reproduce this failure, it varies too much between different standard libraries and os kernels, when a wakeup is triggered. So I can't provide any reference code to demonstrate it.

[vicuna]

Comment author: @xavierleroy

Well spotted, thanks. Tentative fix on SVN trunk, revision 16490.

[vicuna]

Comment author: sebmondet

Hi (I'm the original poster of ocsigen/lwt#186)

I had that bug happening relatively often (but only on MacOSX I think).

I've been trying since yesterday with Xavier's commit: 307f55a
on top of 4.02.3
(cf. https://github.com/smondet/ocaml/tree/4203_fix7013)
(because dependencies of my project do not build with trunk).

I haven't seen any thread dying with the backtrace so far with the patch in.