my Guess
problem may be in readXML; or writeValueXML; or appendLoggedFile;
Are you using any global array to push the contents read from the devices?, so that the array grows huge
If you are using *nix you can check with 'top' command to see the memory usage of the program, if it is huge then you might have made a mess with handling variables.
With the data provided I can't come to any conclusion.
.
Vivek
-- In accordance with the prarabdha of each, the One whose function it is to ordain makes each to act. What will not happen will never happen, whatever effort one may put forth. And what will happen will not fail to happen, however much one may seek to prevent it. This is certain. The part of wisdom therefore is to stay quiet.