This patch fixes a potential busy-loop in the thread scheduler. If there
are two threads, the main thread (where Ruby signal handlers must run)
and a sleeping thread, it is possible for the following sequence of
events to occur:
* The sleeping thread is in native_sleep -> sigwait_sleep A signal
* arives, kicking this thread out of rb_sigwait_sleep The sleeping
* thread calls THREAD_BLOCKING_END and eventually
thread_sched_to_running_common
* the sleeping thread writes into the sigwait_fd pipe by calling
rb_thread_wakeup_timer_thread
* the sleeping thread re-loops around in native_sleep() because
the desired sleep time has not actually yet expired
* that calls rb_sigwait_sleep again the ppoll() in rb_sigwait_sleep
* immediately returns because
of the byte written into the sigwait_fd by
rb_thread_wakeup_timer_thread
* that wakes the thread up again and kicks the whole cycle off again.
Such a loop can only be broken by the main thread waking up and handling
the signal, such that ubf_threads_empty() below becomes true again;
however this loop can actually keep things so busy (and cause so much
contention on the main thread's interrupt_lock) that the main thread
doesn't deal with the signal for many seconds. This seems particuarly
likely on FreeBSD 13.
(the cycle can also be broken by the sleeping thread finally elapsing
its desired sleep time).
The fix for _this_ loop is to only wakeup the timer thrad in
thread_sched_to_running_common if the current thread is not itself the
sigwait thread.
An almost identical loop also happens in the same circumstances because
the call to check_signals_nogvl (through sigwait_timeout) in
rb_sigwait_sleep returns true if there is any pending signal for the
main thread to handle. That then causes rb_sigwait_sleep to skip over
sleeping entirely.
This is unnescessary and counterproductive, I believe; if the main
thread needs to be woken up that is done inline in check_signals_nogvl
anyway.
See https://bugs.ruby-lang.org/issues/19680
because of 9720f5ac8920230403T130011Z.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.
* Revert "Remove special handling of `SIGCHLD`. (#7482)"
This reverts commit 44a0711eab.
* Revert "Remove prototypes for functions that are no longer used. (#7497)"
This reverts commit 4dce12bead.
* Revert "Remove SIGCHLD `waidpid`. (#7476)"
This reverts commit 1658e7d966.
* Fix change to rjit variable name.
It's possible (but very rare) to have a race condition between setting
`mutex->fiber = NULL` and `thread_mutex_remove(th, mutex)` which results
in the following bug:
```
[BUG] invalid keeping_mutexes: Attempt to unlock a mutex which is not locked
```
Fixes <https://bugs.ruby-lang.org/issues/19480>.
```
1) Failure:
TestThreadInstrumentation#test_thread_instrumentation [/tmp/ruby/src/trunk-repeat20-asserts/test/-ext-/thread/test_instrumentation_api.rb:33]:
Call counters[4]: [3, 4, 4, 4, 0].
Expected 0 to be > 0.
```
We fire the EXIT hook after the call to `thread_sched_to_dead` which
mean another thread might be running before the `EXIT` hook have been
executed.
[Bug #19415]
If multiple threads attemps to load the same file concurrently
it's not a circular dependency issue.
So we check that the existing ThreadShield is owner by the current
fiber before warning about circular dependencies.
[Bug #19415]
If multiple threads attemps to load the same file concurrently
it's not a circular dependency issue.
So we check that the existing ThreadShield is owner by the current
fiber before warning about circular dependencies.
First, rb_mjit_fork should call rb_thread_atfork to stop threads after
fork in the child process. Unfortunately, we cannot use rb_fork_ruby to
prevent this kind of mistakes because MJIT needs special handling of
waiting_pid and mjit_pause/resume.
Second, mjit_waitpid_finished should be checked regardless of
trap_interrupt. It doesn't seem like the flag is not set when SIGCHLD is
handled for an MJIT child process.
GCC warns of empty format strings, perhaps because they have no
effects in printf() and there are better ways than sprintf().
However, ruby_debug_log() adds informations other than the format,
this warning is not the case.
rb_ary_tmp_new suggests that the array is temporary in some way, but
that's not true, it just creates an array that's hidden and not on the
transient heap. This commit renames it to rb_ary_hidden_new.
`rb_thread_wait_for_single_fd` needs to mutate the `waiting_fds` list
that is stored on the VM. We need to delete the FD from the list before
returning, and deleting from the list requires a VM lock (because the
list is a global).
[Bug #18816] [ruby-core:108771]
Co-Authored-By: Alan Wu <alanwu@ruby-lang.org>
[Feature #18339]
After experimenting with the initial version of the API I figured there is a need
for an exit event to cleanup instrumentation data. e.g. if you record data in a
{thread_id -> data} table, you need to free associated data when a thread goes away.
Previously, because opt_aref and opt_aset don't push a frame, when they
would call rb_hash to determine the hash value of the key, the initial
level of recursion would incorrectly use the method id at the top of the
stack instead of "hash".
This commit replaces rb_exec_recursive_outer with
rb_exec_recursive_outer_mid, which takes an explicit method id, so that
we can make the hash calculation behave consistently.
rb_exec_recursive_outer was documented as being internal, so I believe
this should be okay to change.
`NON_SCALAR_THREAD_ID` shows `pthread_t` is non-scalar (non-pointer)
and only s390x is known platform. However, the supporting code is
very complex and it is only used for deubg print information.
So this patch removes the support of `NON_SCALAR_THREAD_ID`
and make the code simple.
