From bc462b7969bf21471b4767af02d497c772dcc12c Mon Sep 17 00:00:00 2001
From: Julien Portalier <julien@portalier.com>
Date: Mon, 12 May 2025 14:48:18 +0200
Subject: [PATCH] Fix: calling Fiber::ExecutionContext#enqueue from bare Thread

A bare thread doesn't have an execution context, yet may be capable to
call Fiber#enqueue to enqueue a fiber back into its original context.
---
 src/fiber/execution_context.cr                 | 7 ++++++-
 src/fiber/execution_context/multi_threaded.cr  | 2 +-
 src/fiber/execution_context/single_threaded.cr | 2 +-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/fiber/execution_context.cr b/src/fiber/execution_context.cr
index 1c1ae2f1eb21..8d2289740ebc 100644
--- a/src/fiber/execution_context.cr
+++ b/src/fiber/execution_context.cr
@@ -122,6 +122,10 @@ module Fiber::ExecutionContext
     Thread.current.execution_context
   end
 
+  def self.current? : ExecutionContext?
+    Thread.current.execution_context?
+  end
+
   # :nodoc:
   #
   # Tells the current scheduler to suspend the current fiber and resume the
@@ -181,6 +185,7 @@ module Fiber::ExecutionContext
   #
   # Enqueues a fiber to be resumed inside the execution context.
   #
-  # May be called from any ExecutionContext (i.e. must be thread-safe).
+  # May be called from any ExecutionContext (i.e. must be thread-safe). May also
+  # be called from bare threads (outside of an ExecutionContext).
   abstract def enqueue(fiber : Fiber) : Nil
 end
diff --git a/src/fiber/execution_context/multi_threaded.cr b/src/fiber/execution_context/multi_threaded.cr
index 9793c5468b0b..e843178d1d10 100644
--- a/src/fiber/execution_context/multi_threaded.cr
+++ b/src/fiber/execution_context/multi_threaded.cr
@@ -180,7 +180,7 @@ module Fiber::ExecutionContext
 
     # :nodoc:
     def enqueue(fiber : Fiber) : Nil
-      if ExecutionContext.current == self
+      if ExecutionContext.current? == self
         # local enqueue: push to local queue of current scheduler
         ExecutionContext::Scheduler.current.enqueue(fiber)
       else
diff --git a/src/fiber/execution_context/single_threaded.cr b/src/fiber/execution_context/single_threaded.cr
index 74ad81ea51ce..f4a2aa4f3694 100644
--- a/src/fiber/execution_context/single_threaded.cr
+++ b/src/fiber/execution_context/single_threaded.cr
@@ -102,7 +102,7 @@ module Fiber::ExecutionContext
 
     # :nodoc:
     def enqueue(fiber : Fiber) : Nil
-      if ExecutionContext.current == self
+      if ExecutionContext.current? == self
         # local enqueue
         Crystal.trace :sched, "enqueue", fiber: fiber
         @runnables.push(fiber)