dump undumpable exceptions without cause if that fixes the issue

lib/parallel.rb

@@ -15,6 +15,17 @@ def initialize(value = nil)
       super()
       @value = value
     end
+
+    # marshal_dump that is used for ruby exceptions
+    # avoid dumping the cause since nobody needs that and it can include undumpable exceptions
+    def _dump(_depth)
+      Marshal.dump(@value)
+    end
+
+    # marshal_load that is used for ruby exceptions
+    def self._load(data)
+      new(Marshal.load(data))
+    end
   end
 
   class Kill < Break

spec/cases/parallel_break_with_undumpable_cause.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+require './spec/cases/helper'
+
+class UndumpableCauseError < StandardError
+  def initialize
+    super("bad")
+    @binding = binding # can't be dumped when it is the cause
+  end
+end
+
+begin
+  x = Parallel.in_processes(2) do
+    raise UndumpableCauseError
+  rescue StandardError
+    raise Parallel::Break, "hello"
+  end
+  puts "Result: #{x}"
+rescue StandardError => e
+  puts "Error: #{e.class}: #{e.message}"
+end

spec/parallel_spec.rb

@@ -180,6 +180,11 @@ def cpus
       out.should == "NOTHING WAS RAISED"
     end
 
+    it "can handle Break with an undumpable cause" do
+      out = ruby("spec/cases/parallel_break_with_undumpable_cause.rb").strip
+      out.should == "Result: hello"
+    end
+
     it 'can handle to high fork rate' do
       next if RbConfig::CONFIG["target_os"].include?("darwin1") # kills macs for some reason
       ruby("spec/cases/parallel_high_fork_rate.rb").should == 'OK'