Why are you opening and closing the file in every iteration of the while loop? Since it looks like you want this loop to run fast, the opening and closing are going to slow things way down.
Why do you have a semaphore set up for disk access? I don't see any other piece of code interacting with this semaphore. Semaphores are used to keep different pieces of code from acting at the same time. But here you only have one piece of code. You also have the operations setup in a Case structure that runs based on whether the semaphore times out. But the semaphore will never time out because you don't have any timeout wired to the acquisition of the semaphore.
How fast do you want the shared variable to be read in the upper left while loop? You don't have any wait time associated with it. It might be running very fast, and possibly getting redundant data from the shared variable. It could be loading up the queue faster than you can dequeue to send the data out to the file operations.
Normal procedure for using queues is to just use the dequeue function. Monitoring the queue status and using queue flush to get all queue elements is a little bit unusual.
