Under the M:N thread scheduler, a Ruby thread in a non-main Ractor may be
resumed on a different native thread after it blocks. The C compiler
assumes that the native thread never changes within a function, so it may
compute the address of ruby_current_ec once (`__tls_get_addr` in
libruby.so) and reuse it after the switch. The address then refers to the
TLS of the previous native thread, which leads to a SEGV or to using
another thread's ec.
8.times.map do
Ractor.new do
50.times do
",,".split(/(,)/) { sleep 0.001 }
end
:ok
end
end.map(&:value)
#=> [BUG] Segmentation fault at 0x0000000000000030 (with Clang 21)
arm64 and ppc64le already use the out-of-line rb_current_ec()
(RB_THREAD_CURRENT_EC_NOINLINE), which prevents the compiler from caching
the address. Use it on all platforms, and remove the macro.
[Bug #22453]
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Windows carried a second, much weaker scheduler: a single Win32 mutex as
the GVL, vm->clock for preemption, its own VM barrier over
vm->ractor.sync.barrier_*, its own Ractor wait/wakeup on a per-Ractor
condvar, no ready queue and no time slice. Keeping two made the rest of
the interpreter branch on which one was compiled in, and left Ractors on
Windows without real scheduling.
Move the scheduler out of thread_pthread.c into thread_sched.c and let
both platforms use it. thread.c now includes thread_sched.c, which
declares the scheduler <-> platform contract, includes THREAD_IMPL_SRC,
and then builds the scheduler on the primitives that file provides.
thread_pthread.c keeps only those primitives: synchronization, thread
local storage, native thread creation and stacks, the communication pipe,
the timer thread backend, the fork lock and the event hooks.
The data structures the scheduler works on move to a new thread_sched.h,
included from both platform headers, so struct rb_thread_sched,
struct rb_native_thread and struct rb_thread_sched_item are now shared.
thread_pthread_mn.c becomes thread_sched_mn.c: it is the M:N scheduler,
not a pthread detail. Most of it -- the coroutine threads, the native
thread stack pool, the timer wheel and the fd -> waiters map -- is
platform independent; only the readiness backend is not, and that section
is now marked as the seam where an epoll/kqueue split (or an IOCP backend,
which is what Windows would need for M:N) would go.
What Windows had to add is small: native_thread_interrupt(),
native_thread_default_max_cpu(), timer_thread_polling(),
timer_thread_wakeup_force(), RB_NATIVE_COND_MONOTONIC_P() and
RB_NATIVE_MUTEX_TRYLOCK_DETECTS_SELF() -- the last because a
CRITICAL_SECTION is recursive, so trylock cannot back a "somebody holds
this" assertion. It sets USE_MN_THREADS to 0 and supplies the stubs
thread_sched_mn.c provides elsewhere, so every thread there is dedicated,
as it already was.
With one scheduler the platform branches go away: all 16 uses of
RUBY_THREAD_PTHREAD_H / RUBY_THREAD_WIN32_H are removed from vm_core.h,
ractor.c, ractor_core.h, ractor_sync.c, vm_sync.c, vm.c and thread.c.
ractor_check_blocking() went with them -- it only ever fed the win32
scheduler's vm->ractor.blocking_cnt -- and so did USE_VM_CLOCK, now that
the common time slice drives preemption on Windows too.
Verified on both platforms. Linux: 11 rounds of make test-all (36236
tests) and btest (2066 tests) with no failures, plus 474 runs of a
scheduler and Ractor stress soak. Windows: no test fails that does not
also fail on the same tree without this change, btest passes, and two
40-minute soaks of 438 and 460 runs are clean. Ractors now run in
parallel there -- 3.6x on four Ractors, where before they could not.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This patch introduce M:N thread scheduler for Ractor system.
In general, M:N thread scheduler employs N native threads (OS threads)
to manage M user-level threads (Ruby threads in this case).
On the Ruby interpreter, 1 native thread is provided for 1 Ractor
and all Ruby threads are managed by the native thread.
From Ruby 1.9, the interpreter uses 1:1 thread scheduler which means
1 Ruby thread has 1 native thread. M:N scheduler change this strategy.
Because of compatibility issue (and stableness issue of the implementation)
main Ractor doesn't use M:N scheduler on default. On the other words,
threads on the main Ractor will be managed with 1:1 thread scheduler.
There are additional settings by environment variables:
`RUBY_MN_THREADS=1` enables M:N thread scheduler on the main ractor.
Note that non-main ractors use the M:N scheduler without this
configuration. With this configuration, single ractor applications
run threads on M:1 thread scheduler (green threads, user-level threads).
`RUBY_MAX_CPU=n` specifies maximum number of native threads for
M:N scheduler (default: 8).
This patch will be reverted soon if non-easy issues are found.
[Bug #19842]
`rb_thread_t` contained `native_thread_data_t` to represent
thread implementation dependent data. This patch separates
them and rename it `rb_native_thread` and point it from
`rb_thraed_t`.
Now, 1 Ruby thread (`rb_thread_t`) has 1 native thread (`rb_native_thread`).
Now GVL is not process *Global* so this patch try to use
another words.
* `rb_global_vm_lock_t` -> `struct rb_thread_sched`
* `gvl->owner` -> `sched->running`
* `gvl->waitq` -> `sched->readyq`
* `rb_gvl_init` -> `rb_thread_sched_init`
* `gvl_destroy` -> `rb_thread_sched_destroy`
* `gvl_acquire` -> `thread_sched_to_running` # waiting -> ready -> running
* `gvl_release` -> `thread_sched_to_waiting` # running -> waiting
* `gvl_yield` -> `thread_sched_yield`
* `GVL_UNLOCK_BEGIN` -> `THREAD_BLOCKING_BEGIN`
* `GVL_UNLOCK_END` -> `THREAD_BLOCKING_END`
* removed
* `rb_ractor_gvl`
* `rb_vm_gvl_destroy` (not used)
There are GVL functions such as `rb_thread_call_without_gvl()` yet
but I don't have good name to replace them. Maybe GVL stands for
"Greate Valuable Lock" or something like that.
