Introduce Ractor mechanism for parallel execution

This commit introduces Ractor mechanism to run Ruby program in
parallel. See doc/ractor.md for more details about Ractor.
See ticket [Feature #17100] to see the implementation details
and discussions.

[Feature #17100]

This commit does not complete the implementation. You can find
many bugs on using Ractor. Also the specification will be changed
so that this feature is experimental. You will see a warning when
you make the first Ractor with `Ractor.new`.

I hope this feature can help programmers from thread-safety issues.

compile.c

@@ -1600,6 +1600,16 @@ iseq_block_param_id_p(const rb_iseq_t *iseq, ID id, int *pidx, int *plevel)
     }
 }
 
+static void
+check_access_outer_variables(const rb_iseq_t *iseq, int level)
+{
+    // set access_outer_variables
+    for (int i=0; i<level; i++) {
+        iseq->body->access_outer_variables = TRUE;
+        iseq = iseq->body->parent_iseq;
+    }
+}
+
 static void
 iseq_add_getlocal(rb_iseq_t *iseq, LINK_ANCHOR *const seq, int line, int idx, int level)
 {
@@ -1609,6 +1619,7 @@ iseq_add_getlocal(rb_iseq_t *iseq, LINK_ANCHOR *const seq, int line, int idx, in
     else {
 	ADD_INSN2(seq, line, getlocal, INT2FIX((idx) + VM_ENV_DATA_SIZE - 1), INT2FIX(level));
     }
+    check_access_outer_variables(iseq, level);
 }
 
 static void
@@ -1620,6 +1631,7 @@ iseq_add_setlocal(rb_iseq_t *iseq, LINK_ANCHOR *const seq, int line, int idx, in
     else {
 	ADD_INSN2(seq, line, setlocal, INT2FIX((idx) + VM_ENV_DATA_SIZE - 1), INT2FIX(level));
     }
+    check_access_outer_variables(iseq, level);
 }
 
 
@@ -8222,6 +8234,8 @@ iseq_compile_each0(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *node, in
 	if (popped) {
 	    ADD_INSN(ret, line, pop);
 	}
+
+        iseq->body->access_outer_variables = TRUE;
 	break;
       }
       case NODE_LVAR:{
@@ -8680,7 +8694,8 @@ iseq_compile_each0(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *node, in
 	VALUE flag = INT2FIX(excl);
 	const NODE *b = node->nd_beg;
 	const NODE *e = node->nd_end;
-	if (optimizable_range_item_p(b) && optimizable_range_item_p(e)) {
+        // TODO: Ractor can not use cached Range objects
+	if (0 && optimizable_range_item_p(b) && optimizable_range_item_p(e)) {
 	    if (!popped) {
                 VALUE bv = nd_type(b) == NODE_LIT ? b->nd_lit : Qnil;
                 VALUE ev = nd_type(e) == NODE_LIT ? e->nd_lit : Qnil;

cont.c

@@ -28,6 +28,7 @@
 #include "mjit.h"
 #include "vm_core.h"
 #include "id_table.h"
+#include "ractor.h"
 
 static const int DEBUG = 0;
 
@@ -808,14 +809,15 @@ static inline void
 ec_switch(rb_thread_t *th, rb_fiber_t *fiber)
 {
     rb_execution_context_t *ec = &fiber->cont.saved_ec;
-
-    ruby_current_execution_context_ptr = th->ec = ec;
+    rb_ractor_set_current_ec(th->ractor, th->ec = ec);
+    // ruby_current_execution_context_ptr = th->ec = ec;
 
     /*
      * timer-thread may set trap interrupt on previous th->ec at any time;
      * ensure we do not delay (or lose) the trap interrupt handling.
      */
-    if (th->vm->main_thread == th && rb_signal_buff_size() > 0) {
+    if (th->vm->ractor.main_thread == th &&
+        rb_signal_buff_size() > 0) {
         RUBY_VM_SET_TRAP_INTERRUPT(ec);
     }
 
@@ -1873,7 +1875,7 @@ rb_fiber_start(void)
     enum ruby_tag_type state;
     int need_interrupt = TRUE;
 
-    VM_ASSERT(th->ec == ruby_current_execution_context_ptr);
+    VM_ASSERT(th->ec == GET_EC());
     VM_ASSERT(FIBER_RESUMED_P(fiber));
 
     if (fiber->blocking) {
@@ -1964,13 +1966,15 @@ rb_threadptr_root_fiber_release(rb_thread_t *th)
         /* ignore. A root fiber object will free th->ec */
     }
     else {
+        rb_execution_context_t *ec = GET_EC();
+
         VM_ASSERT(th->ec->fiber_ptr->cont.type == FIBER_CONTEXT);
         VM_ASSERT(th->ec->fiber_ptr->cont.self == 0);
-        fiber_free(th->ec->fiber_ptr);
 
-        if (th->ec == ruby_current_execution_context_ptr) {
-            ruby_current_execution_context_ptr = NULL;
+        if (th->ec == ec) {
+            rb_ractor_set_current_ec(th->ractor, NULL);
         }
+        fiber_free(th->ec->fiber_ptr);
         th->ec = NULL;
     }
 }

debug.c

@@ -26,6 +26,7 @@
 #include "vm_debug.h"
 #include "vm_callinfo.h"
 #include "ruby/thread_native.h"
+#include "ractor.h"
 
 /* This is the only place struct RIMemo is actually used */
 struct RIMemo {
@@ -422,7 +423,6 @@ ruby_debug_log(const char *file, int line, const char *func_name, const char *fm
         len += r;
     }
 
-#if 0 // not yet
     // ractor information
     if (GET_VM()->ractor.cnt > 1) {
         rb_ractor_t *cr = GET_RACTOR();
@@ -433,7 +433,6 @@ ruby_debug_log(const char *file, int line, const char *func_name, const char *fm
             len += r;
         }
     }
-#endif
 
     // thread information
     if (!rb_thread_alone()) {