Fix deadlock of Future when the handler raises Exception

Author: amutake

lib/concurrent/future.rb

@@ -82,7 +82,7 @@ def self.execute(opts = {}, &block)
 
     # @!visibility private
     def work # :nodoc:
-      success, val, reason = SafeTaskExecutor.new(@task).execute(*@args)
+      success, val, reason = SafeTaskExecutor.new(@task, rescue_exception: true).execute(*@args)
       complete(success, val, reason)
     end
   end

spec/concurrent/future_spec.rb

@@ -204,6 +204,11 @@ def trigger_observable(observable)
         expect(future.value).to be_nil
       end
 
+      it 'sets the value to nil when the handler raises Exception' do
+        future = Future.new(executor: executor){ raise Exception }.execute
+        expect(future.value).to be_nil
+      end
+
       it 'sets the state to :rejected when the handler raises an exception' do
         future = Future.new(executor: executor){ raise StandardError }.execute
         expect(future).to be_rejected