Thread owns its current fiber (instead of Crystal::Scheduler)

src/crystal/scheduler.cr

@@ -24,10 +24,6 @@ class Crystal::Scheduler
     Thread.current.scheduler.@event_loop
   end
 
-  def self.current_fiber : Fiber
-    Thread.current.scheduler.@current
-  end
-
   def self.enqueue(fiber : Fiber) : Nil
     thread = Thread.current
     scheduler = thread.scheduler
@@ -98,10 +94,9 @@ class Crystal::Scheduler
   @sleeping = false
 
   # :nodoc:
-  def initialize(thread : Thread)
+  def initialize(@thread : Thread)
     @main = thread.main_fiber
     {% if flag?(:preview_mt) %} @main.set_current_thread(thread) {% end %}
-    @current = @main
     @runnables = Deque(Fiber).new
   end
 
@@ -124,7 +119,7 @@ class Crystal::Scheduler
       GC.set_stackbottom(fiber.@stack_bottom)
     {% end %}
 
-    current, @current = @current, fiber
+    current, @thread.current_fiber = @thread.current_fiber, fiber
     Fiber.swapcontext(pointerof(current.@context), pointerof(fiber.@context))
 
     {% if flag?(:preview_mt) %}
@@ -151,7 +146,7 @@ class Crystal::Scheduler
   protected def reschedule : Nil
     loop do
       if runnable = @lock.sync { @runnables.shift? }
-        resume(runnable) unless runnable == @current
+        resume(runnable) unless runnable == @thread.current_fiber
         break
       else
         @event_loop.run_once
@@ -160,12 +155,12 @@ class Crystal::Scheduler
   end
 
   protected def sleep(time : Time::Span) : Nil
-    @current.resume_event.add(time)
+    @thread.current_fiber.resume_event.add(time)
     reschedule
   end
 
   protected def yield(fiber : Fiber) : Nil
-    @current.resume_event.add(0.seconds)
+    @thread.current_fiber.resume_event.add(0.seconds)
     resume(fiber)
   end
 

src/crystal/system/thread.cr

@@ -45,6 +45,9 @@ class Thread
   # Returns the Fiber representing the thread's main stack.
   getter! main_fiber : Fiber
 
+  # Returns the Fiber currently running on the thread.
+  property! current_fiber : Fiber
+
   # :nodoc:
   property next : Thread?
 
@@ -68,7 +71,7 @@ class Thread
   def initialize
     @func = ->(t : Thread) {}
     @system_handle = Crystal::System::Thread.current_handle
-    @main_fiber = Fiber.new(stack_address, self)
+    @current_fiber = @main_fiber = Fiber.new(stack_address, self)
 
     Thread.threads.push(self)
   end
@@ -120,7 +123,7 @@ class Thread
   protected def start
     Thread.threads.push(self)
     Thread.current = self
-    @main_fiber = fiber = Fiber.new(stack_address, self)
+    @current_fiber = @main_fiber = fiber = Fiber.new(stack_address, self)
 
     if name = @name
       self.system_name = name

src/fiber.cr

@@ -173,7 +173,7 @@ class Fiber
 
   # Returns the current fiber.
   def self.current : Fiber
-    Crystal::Scheduler.current_fiber
+    Thread.current.current_fiber
   end
 
   # The fiber's proc is currently running or didn't fully save its context. The
@@ -246,11 +246,11 @@ class Fiber
   # The current fiber will resume after a period of time.
   # The timeout can be cancelled with `cancel_timeout`
   def self.timeout(timeout : Time::Span?, select_action : Channel::TimeoutAction? = nil) : Nil
-    Crystal::Scheduler.current_fiber.timeout(timeout, select_action)
+    Fiber.current.timeout(timeout, select_action)
   end
 
   def self.cancel_timeout : Nil
-    Crystal::Scheduler.current_fiber.cancel_timeout
+    Fiber.current.cancel_timeout
   end
 
   # Yields to the scheduler and allows it to swap execution to other

src/gc/boehm.cr

@@ -374,8 +374,7 @@ module GC
 
       {% if flag?(:preview_mt) %}
         Thread.unsafe_each do |thread|
-          if scheduler = thread.@scheduler
-            fiber = scheduler.@current
+          if fiber = thread.current_fiber?
             GC.set_stackbottom(thread.gc_thread_handler, fiber.@stack_bottom)
           end
         end