From 23a4e7149dc4253caf5ed0a528ffe5c21c4afb80 Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Mon, 11 Jun 2018 14:50:42 +0900
Subject: Revert "No longer need to insert write barriers for fibers."

This reverts commit c6736357a72049a0eb2a31ccabcc3cd2baba7c9e.
The assumption was wrong and caused the issue; fix #4020
---
 mrbgems/mruby-fiber/src/fiber.c |  3 +++
 src/vm.c                        | 10 +++++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/mrbgems/mruby-fiber/src/fiber.c b/mrbgems/mruby-fiber/src/fiber.c
index b88fa4949..bff8726a7 100644
--- a/mrbgems/mruby-fiber/src/fiber.c
+++ b/mrbgems/mruby-fiber/src/fiber.c
@@ -175,6 +175,9 @@ fiber_check_cfunc(mrb_state *mrb, struct mrb_context *c)
 static void
 fiber_switch_context(mrb_state *mrb, struct mrb_context *c)
 {
+  if (mrb->c->fib) {
+    mrb_write_barrier(mrb, (struct RBasic*)mrb->c->fib);
+  }
   c->status = MRB_FIBER_RUNNING;
   mrb->c = c;
 }
diff --git a/src/vm.c b/src/vm.c
index 552bc8072..43efaa669 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -949,7 +949,12 @@ mrb_vm_run(mrb_state *mrb, struct RProc *proc, mrb_value self, unsigned int stac
   if (c->ci - c->cibase > cioff) {
     c->ci = c->cibase + cioff;
   }
-  mrb->c = c;
+  if (mrb->c != c) {
+    if (mrb->c->fib) {
+      mrb_write_barrier(mrb, (struct RBasic*)mrb->c->fib);
+    }
+    mrb->c = c;
+  }
   return result;
 }
 
@@ -1942,6 +1947,9 @@ RETRY_TRY_BLOCK:
                 while (c->eidx > ci->epos) {
                   ecall_adjust();
                 }
+                if (c->fib) {
+                  mrb_write_barrier(mrb, (struct RBasic*)c->fib);
+                }
                 mrb->c->status = MRB_FIBER_TERMINATED;
                 mrb->c = c->prev;
                 c->prev = NULL;
-- 
cgit v1.2.3