smol hacks fix

src/hacks.cr

@@ -57,27 +57,35 @@ class Fiber
 		if handler = Hacks.fiber_on_unhandled_exception
 			handler.call ex
 		else
+			io = {% if flag?(:preview_mt) %}
+					IO::Memory.new(4096) # PIPE_BUF
+				{% else %}
+					STDERR
+				{% end %}
 			if name = @name
-				STDERR.print "Unhandled exception in spawn (name: #{name}): "
+				io << "Unhandled exception in spawn(name: " << name << "): "
 			else
-				STDERR.print "Unhandled exception in spawn: "
+				io << "Unhandled exception in spawn: "
 			end
-			ex.inspect_with_backtrace(STDERR)
+			ex.inspect_with_backtrace(io)
+			{% if flag?(:preview_mt) %}
+				STDERR.write(io.to_slice)
+			{% end %}
 			STDERR.flush
 		end
 	ensure
 		# Remove the current fiber from the linked list
-	    Fiber.inactive(self)
+		Fiber.inactive(self)
 
-	    # Delete the resume event if it was used by `yield` or `sleep`
-	    @resume_event.try &.free
-	    @timeout_event.try &.free
-	    @timeout_select_action = nil
+		# Delete the resume event if it was used by `yield` or `sleep`
+		@resume_event.try &.free
+		@timeout_event.try &.free
+		@timeout_select_action = nil
 
-	    @alive = false
-	    {% unless flag?(:interpreted) %}
-	      Crystal::Scheduler.stack_pool.release(@stack)
-	    {% end %}
-	    Crystal::Scheduler.reschedule
+		@alive = false
+		{% unless flag?(:interpreted) %}
+			Crystal::Scheduler.stack_pool.release(@stack)
+		{% end %}
+		Fiber.suspend
 	end
 end