sharedtables.withValue causes deadlock on OSX (cf recent CI freezes)

[timotheecour]

refs #18172 (comment)

Example

when true:
  import std/sharedtables
  var table: SharedTable[string, string]
  init(table)

  table["a"] = "x"
  table["b"] = "y"
  table["c"] = "z"


  table.withValue("a", value):
    value[] = "m"

  table.withValue("d", value):
    discard value
    doAssert false
  do: # if "d" notin table
    table["d"] = "n"

  assert table.mget("a") == "m"
  assert table.mget("d") == "n"

Current Output

hangs, after ^C I get:

Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t12358.nim(22) t12358
/Users/timothee/git_clone/nim/Nim_devel/lib/pure/collections/sharedtables.nim(57) []=
SIGINT: Interrupted by Ctrl-C.

Expected Output

works

Additional Information

• 1.5.1 654a201
• after fixing, workaround bug in sharedtables.withValue to unblock frozen CI on OSX #18172 should be reverted
• sharedtables does not have pairs or keys iterator #17697 was tracking a different problem with withValue, so i didnt' merge it in that issue

[ringabout]

The dead locks happened on linux too which is consistent with what it should be.

--threads:off: compiles and runs.
--threads:on: hangs

Works on windows with/without threads options because the locks module uses reentrant mutex on windows.

[timotheecour]

on osx, compilation works fine, and running hangs regardless of --threads:on|off

[timotheecour]

ok now I remember I actually looked into related issues a while back:

• bugs with SharedTable timotheecour/Nim#103
• refactoring and yak shaving. #13687 (comment)
• => fix locks timotheecour/Nim#748 WIP to fix locks silently ignoring errors)