Fix interrupt handling in Bundler workers

SharedHelpers.trap failed when the previous handler for a signal is not callable
(for example, when it is the string "DEFAULT").

Instead, we now handle interrupts by aborting the process when worker threads are
running, and restore the previous handler after worker threads are finished.

Fixes rubygems#4764.

bundler/lib/bundler/shared_helpers.rb

@@ -145,13 +145,6 @@ def print_major_deprecations!
       Bundler.ui.warn message
     end
 
-    def trap(signal, override = false, &block)
-      prior = Signal.trap(signal) do
-        block.call
-        prior.call unless override
-      end
-    end
-
     def ensure_same_dependencies(spec, old_deps, new_deps)
       new_deps = new_deps.reject {|d| d.type == :development }
       old_deps = old_deps.reject {|d| d.type == :development }

bundler/lib/bundler/worker.rb

@@ -26,7 +26,6 @@ def initialize(size, name, func)
       @func = func
       @size = size
       @threads = nil
-      SharedHelpers.trap("INT") { abort_threads }
     end
 
     # Enqueue a request to be executed in the worker pool
@@ -68,13 +67,16 @@ def apply_func(obj, i)
     # so as worker threads after retrieving it, shut themselves down
     def stop_threads
       return unless @threads
+
       @threads.each { @request_queue.enq POISON }
       @threads.each(&:join)
+
+      remove_interrupt_handler
+
       @threads = nil
     end
 
     def abort_threads
-      return unless @threads
       Bundler.ui.debug("\n#{caller.join("\n")}")
       @threads.each(&:exit)
       exit 1
@@ -94,11 +96,21 @@ def create_threads
         end
       end.compact
 
+      add_interrupt_handler unless @threads.empty?
+
       return if creation_errors.empty?
 
       message = "Failed to create threads for the #{name} worker: #{creation_errors.map(&:to_s).uniq.join(", ")}"
       raise ThreadCreationError, message if @threads.empty?
       Bundler.ui.info message
     end
+
+    def add_interrupt_handler
+      @previous_interrupt_handler = trap("INT") { abort_threads }
+    end
+
+    def remove_interrupt_handler
+      trap "INT", @previous_interrupt_handler
+    end
   end
 end