relax Fiber#transfer's restriction

Using Fiber#transfer with Fiber#resume for a same Fiber is
limited (once Fiber#transfer is called for a fiber, the fiber
can not be resumed more). This restriction was introduced to
protect the resume/yield chain, but we realized that it is too much
to protect the chain. Instead of the current restriction, we
introduce some other protections.

(1) can not transfer to the resuming fiber.
(2) can not transfer to the yielding fiber.
(3) can not resume transferred fiber.
(4) can not yield from not-resumed fiber.

[Bug #17221]

Also at the end of a transferred fiber, it had continued on root fiber.
However, if the root fiber resumed a fiber (and that fiber can resumed
another fiber), this behavior also breaks the resume/yield chain.
So at the end of a transferred fiber, switch to the edge of resume
chain from root fiber.
For example, root fiber resumed f1 and f1 resumed f2, transferred to
f3 and f3 terminated, then continue from the fiber f2 (it was continued
from root fiber without this patch).

1 files changed, 87 insertions, 16 deletions

diff --git a/test/ruby/test_fiber.rb b/test/ruby/test_fiber.rb
index 4d103a7f76..dc46b558f0 100644
--- a/test/ruby/test_fiber.rb
+++ b/test/ruby/test_fiber.rb
@@ -184,6 +184,34 @@ class TestFiber < Test::Unit::TestCase
     assert_equal([:baz], ary)
   end
 
+  def test_terminate_transferred_fiber
+    root_fiber = Fiber.current
+    log = []
+    fa1 = fa2 = fb1 = r1 = nil
+
+    fa1 = Fiber.new{
+      fa2 = Fiber.new{
+        log << :fa2_terminate
+      }
+      fa2.resume
+      log << :fa1_terminate
+    }
+    fb1 = Fiber.new{
+      fa1.transfer
+      log << :fb1_terminate
+    }
+
+    r1 = Fiber.new{
+      fb1.transfer
+      log << :r1_terminate
+    }
+
+    r1.resume
+    log << :root_terminate
+
+    assert_equal [:fa2_terminate, :fa1_terminate, :r1_terminate, :root_terminate], log
+  end
+
   def test_tls
     #
     def tvar(var, val)
@@ -278,29 +306,72 @@ class TestFiber < Test::Unit::TestCase
     assert_instance_of(Class, Fiber.new(&Class.new.method(:undef_method)).resume(:to_s), bug5083)
   end
 
-  def test_prohibit_resume_transferred_fiber
+  def test_prohibit_transfer_to_resuming_fiber
+    root_fiber = Fiber.current
+
     assert_raise(FiberError){
-      root_fiber = Fiber.current
-      f = Fiber.new{
-        root_fiber.transfer
-      }
-      f.transfer
-      f.resume
+      fiber = Fiber.new{ root_fiber.transfer }
+      fiber.resume
+    }
+
+    fa1 = Fiber.new{
+      fa2 = Fiber.new{ root_fiber.transfer }
+    }
+    fb1 = Fiber.new{
+      fb2 = Fiber.new{ root_fiber.transfer }
+    }
+    fa1.transfer
+    fb1.transfer
+
+    assert_raise(FiberError){
+      fa1.transfer
     }
     assert_raise(FiberError){
-      g=nil
-      f=Fiber.new{
-        g.resume
-        g.resume
-      }
-      g=Fiber.new{
-        f.resume
-        f.resume
+      fb1.transfer
+    }
+  end
+
+  def test_prohibit_transfer_to_yielding_fiber
+    root_fiber = Fiber.current
+    f1 = f2 = f3 = nil
+
+    f1 = Fiber.new{
+      f2 = Fiber.new{
+        f3 = Fiber.new{
+          p f3: Fiber.yield
+        }
+        f3.resume
       }
-      f.transfer
+      f2.resume
     }
+    f1.resume
+
+    assert_raise(FiberError){ f3.transfer 10 }
   end
 
+  def test_prohibit_resume_to_transferring_fiber
+    root_fiber = Fiber.current
+
+    assert_raise(FiberError){
+      Fiber.new{
+        root_fiber.resume
+      }.transfer
+    }
+
+    f1 = f2 = nil
+    f1 = Fiber.new do
+      f2.transfer
+    end
+    f2 = Fiber.new do
+      f1.resume # attempt to resume transferring fiber
+    end
+
+    assert_raise(FiberError){
+      f1.transfer
+    }
+  end
+
+
   def test_fork_from_fiber
     skip 'fork not supported' unless Process.respond_to?(:fork)
     pid = nil