Segmentation fault when changing value of attribute

I'm working in a C++11 class that will fetch via I2C the value of a temperature sensor in a Raspberry Pi. It will be polling the value until it's stopped. It does the polling in a separate thread, so that it does not stop the application flow. The problem is that in the line 64 of this file: http://ift.tt/1zvce6P

it gives a segmentation fault. The curius thing is that it does not always happen. After compiling, running the binary many times about the 75% of the time will crash.

This is the file that invoques the code:http://ift.tt/1ytQMee

What could be happening? How can it be fixed?