BetterErrors.use_pry! works on threaded servers

lib/better_errors/repl/pry.rb

@@ -37,15 +37,36 @@ def print(*args)
       end
 
       def initialize(binding, exception)
-        @fiber = Fiber.new do
-          @pry.repl binding
-        end
+        @input_queue = Queue.new
+        @output_queue = Queue.new
         @input = BetterErrors::REPL::Pry::Input.new
         @output = BetterErrors::REPL::Pry::Output.new
-        @pry = ::Pry.new input: @input, output: @output
-        @pry.hooks.clear_all if defined?(@pry.hooks.clear_all)
-        store_last_exception exception
-        @fiber.resume
+        @thread = Thread.new do
+          Thread.current.abort_on_exception = true
+          @fiber = Fiber.new do
+            @pry.repl binding
+          end
+          @pry = ::Pry.new input: @input, output: @output
+          @pry.hooks.clear_all if defined?(@pry.hooks.clear_all)
+          store_last_exception exception
+          @fiber.resume
+
+          loop do
+            command = @input_queue.shift
+            break if command == :stop
+            local ::Pry.config, color: false, pager: false do
+              @fiber.resume "#{command}\n"
+            end
+            # NOTE: indent_level here is not what we seem to expect it to be ¯\_(ツ)_/¯
+            indent_level = @pry.instance_variable_get(:@indent).indent_level
+            @output_queue << [@output.read_buffer, *prompt(indent_level)]
+          end
+        end
+      end
+
+      def stop
+        @input_queue << :stop
+        @thread.join
       end
 
       def store_last_exception(exception)
@@ -54,23 +75,20 @@ def store_last_exception(exception)
       end
 
       def send_input(str)
-        local ::Pry.config, color: false, pager: false do
-          @fiber.resume "#{str}\n"
-          [@output.read_buffer, *prompt]
-        end
+        @input_queue << str
+        @output_queue.shift
       end
 
-      def prompt
-        if indent = @pry.instance_variable_get(:@indent) and !indent.indent_level.empty?
-          ["..", indent.indent_level]
-        else
+    private
+
+      def prompt(indent_level)
+        if indent_level.empty?
           [">>", ""]
+        else
+          ["..", indent_level]
         end
-      rescue
-        [">>", ""]
       end
 
-    private
       def local(obj, attrs)
         old_attrs = {}
         attrs.each do |k, v|