Add IO tests

[shym]

Add tests for In_channel and Out_channel.
Rebase and fix @OlivierNicole’s Lin tests (#13). Add tests using the Lin DSL.

[shym]

These tests take quite some time, in particular Lin_thread ones, as we would expect. They didn’t trigger any crash in repeated runs (1, 2).
I wonder about exceptions appearing in log: should they not be caught up?

Anyway, should these tests be disabled in standard runs?

[shym]

I’m not sure I understand the issue in that run
https://github.com/shym/multicoretests/actions/runs/3732837838/jobs/6332819522#step:10:406
but so I added exceptions as possible results for Out_channel.close.

[jmid]

Modulo the failing trunk workflows (and me messing up the debug label) this is starting to turn green.

I was just looking at the log and spotted this gem from macOS 5.0.0:
https://github.com/ocaml-multicore/multicoretests/actions/runs/3733518141/jobs/6334412511#step:10:567

random seed: 173862660
generated error fail pass / total     time test name

[ ]    0    0    0    0 / 1000     0.0s Lin DSL In_channel test with Domain
[ ]    0    0    0    0 / 1000     0.0s Lin DSL In_channel test with Domain (generating)
[✓]   10    0    1    9 / 1000    23.8s Lin DSL In_channel test with Domain

[ ]    0    0    0    0 / 1000     0.0s Lin DSL Out_channel test with Domain
[ ]   38    0    0   38 / 1000    37.1s Lin DSL Out_channel test with Domain
[ ]   57    0    0   57 / 1000   181.9s Lin DSL Out_channel test with Domain
[ ]   70    0    0   70 / 1000   524.2s Lin DSL Out_channel test with Domain
[ ]  104    0    0  104 / 1000   584.7s Lin DSL Out_channel test with Domain
[ ]  112    0    0  112 / 1000   644.9s Lin DSL Out_channel test with Domain (shrinking:   26.0018)
[ ]  112    0    0  112 / 1000   705.0s Lin DSL Out_channel test with Domain (shrinking:   36.0052)
[ ]  112    0    0  112 / 1000   765.0s Lin DSL Out_channel test with Domain (shrinking:   47.0005)
[ ]  112    0    0  112 / 1000   825.1s Lin DSL Out_channel test with Domain (shrinking:   61.0009)
[ ]  112    0    0  112 / 1000   885.2s Lin DSL Out_channel test with Domain (shrinking:   73.0011)
[ ]  112    0    0  112 / 1000   945.2s Lin DSL Out_channel test with Domain (shrinking:   87.0015)
[ ]  112    0    0  112 / 1000  1005.4s Lin DSL Out_channel test with Domain (shrinking:  106.0014)
[ ]  112    0    0  112 / 1000  1065.6s Lin DSL Out_channel test with Domain (shrinking:  126.0007)
[ ]  112    0    0  112 / 1000  1125.6s Lin DSL Out_channel test with Domain (shrinking:  145.0013)
[ ]  112    0    0  112 / 1000  1185.7s Lin DSL Out_channel test with Domain (shrinking:  159.0003)
[ ]  112    0    0  112 / 1000  1246.1s Lin DSL Out_channel test with Domain (shrinking:  168.0015)
[ ]  112    0    0  112 / 1000  1306.3s Lin DSL Out_channel test with Domain (shrinking:  179.0005)
[ ]  112    0    0  112 / 1000  1366.3s Lin DSL Out_channel test with Domain (shrinking:  188.0013)
[ ]  112    0    0  112 / 1000  1426.6s Lin DSL Out_channel test with Domain (shrinking:  198.0006)
[ ]  112    0    0  112 / 1000  1486.7s Lin DSL Out_channel test with Domain (shrinking:  213.0005)
[ ]  112    0    0  112 / 1000  1546.9s Lin DSL Out_channel test with Domain (shrinking:  228.0002)
[ ]  112    0    0  112 / 1000  1607.0s Lin DSL Out_channel test with Domain (shrinking:  244.0003)
[ ]  112    0    0  112 / 1000  1667.0s Lin DSL Out_channel test with Domain (shrinking:  255.0007)
[ ]  112    0    0  112 / 1000  1727.1s Lin DSL Out_channel test with Domain (shrinking:  269.0011)
[ ]  112    0    0  112 / 1000  1787.2s Lin DSL Out_channel test with Domain (shrinking:  280)
[ ]  112    0    0  112 / 1000  1847.3s Lin DSL Out_channel test with Domain (shrinking:  291.0018)
[ ]  112    0    0  112 / 1000  1907.6s Lin DSL Out_channel test with Domain (shrinking:  302.0018)
[ ]  112    0    0  112 / 1000  1968.2s Lin DSL Out_channel test with Domain (shrinking:  316.0006)
[ ]  112    0    0  112 / 1000  2028.3s Lin DSL Out_channel test with Domain (shrinking:  330.0011)
[✓]  113    0    1  112 / 1000  2054.8s Lin DSL Out_channel test with Domain

--- Info -----------------------------------------------------------------------

Negative test Lin DSL In_channel test with Domain failed as expected (42 shrink steps):

                                            |                 
                                   In_channel.seek t 4        
                                 In_channel.close_noerr t     
                                   In_channel.seek t 0        
                                 In_channel.input_byte t      
                            In_channel.set_binary_mode t false
                                   In_channel.seek t 72       
                                            |                 
                          .-----------------------------------.
                          |                                   |                 


+++ Messages ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Messages for test Lin DSL In_channel test with Domain:

  Results incompatible with sequential execution

                                                                     |                               
                                                       In_channel.seek t 4 : Ok (())                 
                                                       In_channel.close_noerr t : ()                 
                                                       In_channel.seek t 0 : Ok (())                 
                                                  In_channel.input_byte t : Ok (Some (0))            
                                               In_channel.set_binary_mode t false : Ok (())          
                                      In_channel.seek t 72 : Error (Sys_error("Bad file descriptor"))
                                                                     |                               
                                    .----------------------------------------------------------------.
                                    |                                                                | 

A sequential execution - which fails with Sys_error("Bad file descriptor") and hence isn't compatible with a ... sequential execution? Could this be because closing an in_channel invalidates it at some non-deterministic time in the future? 🤔

[shym]

The runtime code that closes a channel (here) doesn’t seem to leave the place for such non-determinism: the descriptor is invalidated while holding the channel lock.
Interestingly, seek can make input_byte succeed by marking old buffer content as valid again, even though close_noerr tried to mark it as invalidated (to ensure further input* on that channel would trigger an exception).
Well, anyway, it clearly doesn’t explain how this could behave differently between sequential and ... sequential runs.

[shym]

After reading the code again, in those circumstances, I think the content of the internal buffer that’s returned when doing the input is not always initialised, which could explain it could vary from one run to another? 🤔
Even if we’re reading from allocated memory (there should be no risk of a big crash there), it should be considered an OCaml bug?

Simple test:

let _ =
  let f = open_in Sys.argv.(0) in
  seek_in f 4 ;
  close_in_noerr f ;
  seek_in f 0 ;
  Printf.printf "Read: %d\n%!" (input_byte f) ;
  Printf.printf "Read: %d\n%!" (input_byte f) ;
  Printf.printf "Read: %d\n%!" (input_byte f) ;
  Printf.printf "Read: %d\n%!" (input_byte f) ;
  Printf.printf "Read: %d\n%!" (input_byte f)

gives:

$ ocamlopt bob.ml -o bob ; ./bob
Read: 0
Read: 0
Read: 0
Read: 0
Fatal error: exception Sys_error("Bad file descriptor")

[shym]

The bug encountered by this strange run was reported in ocaml/ocaml#11878.

[jmid]

Should we rebase this to have a clean CI run? (the previous one had several unrelated CI failures adding noise)

[jmid]

This looks all green, modulo a threadomain Windows crash.
Also, the timings to run these look reasonable to me.
OK to merge @shym?

[shym]

Let’s!