AtomicMarkableReference: Add try_update_no_exception

In order to avoid raising errors (which are costly to performance), add an API
for attempting an update which simply returns nil to the caller.

Author: ianks

lib/concurrent/atomic/atomic_markable_reference.rb

@@ -147,6 +147,27 @@ def try_update
         ImmutableArray[new_val, new_mark]
       end
 
+      # @!macro [attach] atomic_markable_reference_method_try_update_no_exception
+      #
+      # Pass the current value to the given block, replacing it with the
+      # block's result. Simply return nil if update fails.
+      #
+      # @yield [Object] Calculate a new value and marked state for the atomic
+      #   reference using given (old) value and (old) marked
+      # @yieldparam [Object] old_val the starting value of the atomic reference
+      # @yieldparam [Boolean] old_mark the starting state of marked
+      #
+      # @return [ImmutableArray] the new value and marked state, or nil if
+      # the update failed
+      def try_update_no_exception
+        old_val, old_mark = @Reference.get
+        new_val, new_mark = yield old_val, old_mark
+
+        return unless compare_and_set old_val, new_val, old_mark, new_mark
+
+        ImmutableArray[new_val, new_mark]
+      end
+
       # Internal/private ImmutableArray for representing pairs
       class ImmutableArray < Array
         def self.new(*args)

spec/concurrent/atomic/atomic_markable_reference_spec.rb

@@ -45,6 +45,25 @@
     end
   end
 
+  describe '#try_update_no_exception' do
+    it 'updates the value and mark' do
+      val, mark = subject.try_update { |v, m| [v + 1, !m] }
+
+      expect(subject.value).to eq 1001
+      expect(val).to eq 1001
+      expect(mark).to eq false
+    end
+
+    it 'returns nil when attempting to set inside of block' do
+      expect do
+        subject.try_update do |v, m|
+          subject.set(1001, false)
+          [v + 1, !m]
+        end.to eq nil
+      end
+    end
+  end
+
   describe '#update' do
     it 'updates the value and mark' do
       val, mark = subject.update { |v, m| [v + 1, !m] }