Some of the users of my application complain that sometimes (in a random way) the settings of my application are getting reverted to their default state (usually after a reb
I'd echo the other answers - that you need to avoid conflicts if you don't want to corrupt the file - and I'd go further to suggest that you're probably misuing SharedPreferences.
SPs are designed to store small pieces of information about your app - user settings like volume or whether music is playing or things like that.
SPs are NOT designed for storing data which changes often and/or large amounts of data and it's a bad idea to try to do this (for the reasons you've discovered and a few others).
Remember that SPs are really just an XML file - you're incurring the overhead of parsing and recreating that every time you change it too!
The idea of an App which updates SPs in more than one thread is a bit mad I think - you need a better way of managing and storing the data you're saving - it will pay-off for you in more than one way...