Ruby

fix deadlock on Thread#join

because of 9720f5ac894566ade2aabcf9adea0a3235de1353

http://rubyci.s3.amazonaws.com/solaris11-sunc/ruby-master/log/20230403T130011Z.fail.html.gz

  1) Failure:
TestThread#test_signal_at_join [/export/home/chkbuild/chkbuild-sunc/tmp/build/20230403T130011Z/ruby/test/ruby/test_thread.rb:1488]:
Exception raised:
<#<fatal:"No live threads left. Deadlock?\n1 threads, 1 sleeps current:0x00891288 main thread:0x00891288\n* #<Thread:0xfef89a18 sleep_forever>\n   rb_thread_t:0x00891288 native:0x00000001 int:0\n   \n">>
Backtrace:
  -:30:in `join'
  -:30:in `block (3 levels) in <main>'
  -:21:in `times'
  -:21:in `block (2 levels) in <main>'.

The mechanism:

• Main thread (M) calls Thread#join
• M: calls sleep_forever()
• M: set th->status = THREAD_STOPPED_FOREVER
• M: do checkints
• M: handle a trap handler with th->status = THREAD_RUNNABLE
• M: thread switch at the end of the trap handler
• Another thread (T) will process Thread#kill by M.
• T: rb_threadptr_join_list_wakeup() at the end of T tris to wakeup M,
  but M's state is runnable because M is handling trap handler and
  just ignore the waking up and terminate T$a
• T: switch to M.
• M: after the trap handler, reset th->status = THREAD_STOPPED_FOREVER
  and check deadlock -> Deadlock because only M is living.

To avoid such situation, add new sleep flags SLEEP_ALLOW_SPURIOUS
and SLEEP_NO_CHECKINTS to skip any check ints.

BTW this is instentional to leave second vm_check_ints_blocking()
without checking SLEEP_NO_CHECKINTS because SLEEP_ALLOW_SPURIOUS
should be specified with SLEEP_NO_CHECKINTS and skipping this
checkints can skip any interrupts.