Make Mutex per-Fiber instead of per-Thread

* Enables Mutex to be used as synchronization between multiple Fibers
  of the same Thread.
* With a Fiber scheduler we can yield to another Fiber on contended
  Mutex#lock instead of blocking the entire thread.
* This also makes the behavior of Mutex consistent across CRuby, JRuby and TruffleRuby.
* [Feature #16792]

1 files changed, 33 insertions, 5 deletions

diff --git a/test/fiber/test_mutex.rb b/test/fiber/test_mutex.rb
index 5179959a6a..393a44fc2f 100644
--- a/test/fiber/test_mutex.rb
+++ b/test/fiber/test_mutex.rb
@@ -14,7 +14,7 @@ class TestFiberMutex < Test::Unit::TestCase
         assert_equal Thread.scheduler, scheduler
 
         mutex.synchronize do
-          assert_nil Thread.scheduler
+          assert Thread.scheduler
         end
       end
     end
@@ -22,7 +22,35 @@ class TestFiberMutex < Test::Unit::TestCase
     thread.join
   end
 
+  def test_mutex_interleaved_locking
+    mutex = Mutex.new
+
+    thread = Thread.new do
+      scheduler = Scheduler.new
+      Thread.current.scheduler = scheduler
+
+      Fiber.schedule do
+        mutex.lock
+        sleep 0.1
+        mutex.unlock
+      end
+
+      Fiber.schedule do
+        mutex.lock
+        sleep 0.1
+        mutex.unlock
+      end
+
+      scheduler.run
+    end
+
+    thread.join
+  end
+
   def test_mutex_deadlock
+    err = /No live threads left. Deadlock\?/
+    assert_in_out_err %W[-I#{__dir__} -], <<-RUBY, ['in synchronize'], err, success: false
+    require 'scheduler'
     mutex = Mutex.new
 
     thread = Thread.new do
@@ -30,18 +58,18 @@ class TestFiberMutex < Test::Unit::TestCase
       Thread.current.scheduler = scheduler
 
       Fiber.schedule do
-        assert_equal Thread.scheduler, scheduler
+        raise unless Thread.scheduler == scheduler
 
         mutex.synchronize do
+          puts 'in synchronize'
           Fiber.yield
         end
       end
 
-      assert_raise ThreadError do
-        mutex.lock
-      end
+      mutex.lock
     end
 
     thread.join
+    RUBY
   end
 end