introduce USE_VM_CLOCK for windows.

The timer function used on windows system set timer interrupt
flag of current main ractor's executing ec and thread can detect
the end of time slice. However, to set all ec->interrupt_flag for
all running ractors, it is requires to synchronize with other ractors.
However, timer thread can not acquire the ractor-wide lock because
of some limitation.

To solve this issue, this patch introduces USE_VM_CLOCK compile option
to introduce rb_vm_t::clock. This clock will be incremented by the
timer thread and each thread can check the incrementing by comparison
with previous checked clock. At last, on windows platform this patch
introduces some overhead, but I think there is no critical performance
issue because of this modification.

1 files changed, 8 insertions, 4 deletions

diff --git a/thread_pthread.c b/thread_pthread.c
index 71667aec69..97879f559a 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -194,6 +194,7 @@ designate_timer_thread(rb_global_vm_lock_t *gvl)
 static void
 do_gvl_timer(rb_global_vm_lock_t *gvl, rb_thread_t *th)
 {
+    rb_vm_t *vm = GET_VM();
     static rb_hrtime_t abs;
     native_thread_data_t *nd = &th->native_thread_data;
 
@@ -208,14 +209,14 @@ do_gvl_timer(rb_global_vm_lock_t *gvl, rb_thread_t *th)
     gvl->timer_err = native_cond_timedwait(&nd->cond.gvlq, &gvl->lock, &abs);
 
     ubf_wakeup_all_threads();
-    ruby_sigchld_handler(GET_VM());
+    ruby_sigchld_handler(vm);
 
     if (UNLIKELY(rb_signal_buff_size())) {
-        if (th == GET_VM()->ractor.main_thread) {
+        if (th == vm->ractor.main_thread) {
             RUBY_VM_SET_TRAP_INTERRUPT(th->ec);
         }
         else {
-            threadptr_trap_interrupt(GET_VM()->ractor.main_thread);
+            threadptr_trap_interrupt(vm->ractor.main_thread);
         }
     }
 
@@ -223,7 +224,10 @@ do_gvl_timer(rb_global_vm_lock_t *gvl, rb_thread_t *th)
      * Timeslice.  Warning: the process may fork while this
      * thread is contending for GVL:
      */
-    if (gvl->owner) timer_thread_function(gvl->owner->ec);
+    if (gvl->owner) {
+        // strictly speaking, accessing "gvl->owner" is not thread-safe
+        RUBY_VM_SET_TIMER_INTERRUPT(gvl->owner->ec);
+    }
     gvl->timer = 0;
 }