Add SharedMemory#write_object and #read_object; add SharedMemoryIO helper.

spec/process_shared/shared_memory_spec.rb

@@ -32,5 +32,30 @@ module ProcessShared
 
       mem.get_int(0).must_equal(1234567)
     end
+
+    describe 'Object dump/load' do
+      it 'writes serialized objects' do
+        mem = SharedMemory.new(1024)
+        pid = fork do
+          mem.write_object(['a', 'b'])
+          Kernel.exit!
+        end
+        ::Process.wait(pid)
+        mem.read_object.must_equal ['a', 'b']
+      end
+      
+      it 'raises IndexError when insufficient space' do
+        mem = SharedMemory.new(2)
+        proc { mem.write_object(['a', 'b']) }.must_raise(IndexError)
+      end
+
+      it 'writes with an offset' do
+        mem = SharedMemory.new(1024)
+        mem.put_object(2, 'string')
+        proc { mem.read_object }.must_raise(TypeError)
+        proc { mem.get_object(0) }.must_raise(TypeError)
+        mem.get_object(2).must_equal 'string'
+      end
+    end
   end
 end