From c8e68b3f2061d6a5dfc220cd60b6a75c646e464b Mon Sep 17 00:00:00 2001
From: Sampo Kuokkanen <sampo.kuokkanen@gmail.com>
Date: Fri, 21 Aug 2026 12:42:22 +0900
Subject: [PATCH] Add specs for Fiber.schedule and Fiber.current_scheduler

Fiber.schedule and Fiber.current_scheduler had no specs. Cover the RuntimeError raised when no scheduler is set, that the scheduler's #fiber hook is called and its return value is what Fiber.schedule hands back, and that Fiber.schedule works from inside a non-blocking Fiber.

Fiber.current_scheduler returns the scheduler only when the current Fiber is non-blocking, which is what separates it from Fiber.scheduler. Cover the root Fiber, blocking and non-blocking Fibers,
---
 core/fiber/current_scheduler_spec.rb | 67 +++++++++++++++++++++++++++
 core/fiber/fixtures/scheduler.rb     |  5 ++
 core/fiber/schedule_spec.rb          | 69 ++++++++++++++++++++++++++++
 3 files changed, 141 insertions(+)
 create mode 100644 core/fiber/current_scheduler_spec.rb
 create mode 100644 core/fiber/schedule_spec.rb

diff --git a/core/fiber/current_scheduler_spec.rb b/core/fiber/current_scheduler_spec.rb
new file mode 100644
index 000000000..fc73c8e6a
--- /dev/null
+++ b/core/fiber/current_scheduler_spec.rb
@@ -0,0 +1,67 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/scheduler'
+
+describe "Fiber.current_scheduler" do
+  it "returns nil when no scheduler is set" do
+    Fiber.scheduler.should == nil
+    Fiber.current_scheduler.should == nil
+  end
+
+  describe "when a scheduler is set" do
+    before :each do
+      @scheduler = FiberSpecs::LoggingScheduler.new
+      Fiber.set_scheduler(@scheduler)
+    end
+
+    after :each do
+      Fiber.set_scheduler(nil)
+    end
+
+    it "returns nil on the root Fiber, which is blocking" do
+      Fiber.current_scheduler.should == nil
+    end
+
+    it "returns the scheduler inside a non-blocking Fiber" do
+      seen = nil
+      Fiber.new(blocking: false) { seen = Fiber.current_scheduler }.resume
+      seen.should.equal?(@scheduler)
+    end
+
+    it "returns nil inside a blocking Fiber, where Fiber.scheduler still returns the scheduler" do
+      seen = nil
+      Fiber.new(blocking: true) { seen = [Fiber.scheduler, Fiber.current_scheduler] }.resume
+      seen.should == [@scheduler, nil]
+    end
+
+    it "returns nil inside a blocking Fiber nested in a non-blocking Fiber" do
+      seen = nil
+      Fiber.new(blocking: false) do
+        Fiber.new(blocking: true) { seen = Fiber.current_scheduler }.resume
+      end.resume
+      seen.should == nil
+    end
+
+    it "returns the scheduler inside a non-blocking Fiber nested in a blocking Fiber" do
+      seen = nil
+      Fiber.new(blocking: true) do
+        Fiber.new(blocking: false) { seen = Fiber.current_scheduler }.resume
+      end.resume
+      seen.should.equal?(@scheduler)
+    end
+
+    it "returns nil inside Fiber.blocking in a non-blocking Fiber" do
+      seen = nil
+      Fiber.new(blocking: false) { Fiber.blocking { seen = Fiber.current_scheduler } }.resume
+      seen.should == nil
+    end
+
+    it "returns the scheduler again after Fiber.blocking returns" do
+      seen = nil
+      Fiber.new(blocking: false) do
+        Fiber.blocking { }
+        seen = Fiber.current_scheduler
+      end.resume
+      seen.should.equal?(@scheduler)
+    end
+  end
+end
diff --git a/core/fiber/fixtures/scheduler.rb b/core/fiber/fixtures/scheduler.rb
index 16bd2f6b4..e29a7bac7 100644
--- a/core/fiber/fixtures/scheduler.rb
+++ b/core/fiber/fixtures/scheduler.rb
@@ -11,6 +11,11 @@ def block(*args)
       Fiber.yield
     end
 
+    def fiber(*args, &block)
+      @events << { event: :fiber, fiber: Fiber.current, args: args }
+      Fiber.new(blocking: false, &block).tap(&:resume)
+    end
+
     def io_wait(*args)
       @events << { event: :io_wait, fiber: Fiber.current, args: args }
       Fiber.yield
diff --git a/core/fiber/schedule_spec.rb b/core/fiber/schedule_spec.rb
new file mode 100644
index 000000000..5eb5b5a9a
--- /dev/null
+++ b/core/fiber/schedule_spec.rb
@@ -0,0 +1,69 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/scheduler'
+
+describe "Fiber.schedule" do
+  describe "when no scheduler is set" do
+    it "raises a RuntimeError" do
+      Fiber.scheduler.should == nil
+
+      -> {
+        Fiber.schedule { }
+      }.should.raise(RuntimeError)
+    end
+  end
+
+  describe "when a scheduler is set" do
+    before :each do
+      @scheduler = FiberSpecs::LoggingScheduler.new
+      Fiber.set_scheduler(@scheduler)
+    end
+
+    after :each do
+      Fiber.set_scheduler(nil)
+    end
+
+    it "calls the scheduler's #fiber hook" do
+      Fiber.schedule { }
+      @scheduler.events.map { |event| event[:event] }.should == [:fiber]
+    end
+
+    it "returns the Fiber which runs the block" do
+      scheduled = nil
+      fiber = Fiber.schedule { scheduled = Fiber.current }
+      fiber.should.equal?(scheduled)
+    end
+
+    it "can be called from inside a non-blocking Fiber" do
+      inner = nil
+
+      outer = Fiber.new(blocking: false) do
+        inner = Fiber.schedule { }
+      end
+      outer.resume
+
+      inner.should.is_a?(Fiber)
+    end
+
+    it "uses the scheduler of the Thread owning the Fiber it is called from" do
+      seen = nil
+
+      outer = Fiber.new(blocking: false) do
+        Fiber.schedule { seen = Fiber.scheduler }
+      end
+      outer.resume
+
+      seen.should.equal?(@scheduler)
+    end
+
+    it "runs the block in a Fiber which sees the scheduler as its current scheduler" do
+      seen = nil
+
+      outer = Fiber.new(blocking: false) do
+        Fiber.schedule { seen = Fiber.current_scheduler }
+      end
+      outer.resume
+
+      seen.should.equal?(@scheduler)
+    end
+  end
+end