Question

I have this situation:

web application with cca 200 concurent requests (Threads) are in need to log something to local filesystem. I have one class to which all threads are placing their calls, and that class internally stores messages to one Array (Vector or ArrayList) which then in turn will be written to filesystem.

Idea is to return from thread’s call ASAP so thread can do it’s job as fast as possible, what thread wanted to log can be written to filesystem later, it is not so crucial.

So, that class in turn removes first element from that list and writes it to filesystem, while in real time there is 10 or 20 threads which are appending new logs at the end of that list.

I would like to use ArrayList since it is not synchronized and therefore thread’s calls will last less, question is:

am I risking deadlocks / data loss? Is it better to use Vector since it is thread safe? Is it slower to use Vector?

Answer 1

Actually both ArrayList and Vector are very bad choices here, not because of synchronization (which you would definitely need), but because removing the first element is O(n).

The perfect data structure for your purspose is the ConcurrentLinkedQueue: it offers both thread safety (without using synchronization), and O(1) adding and removing.