Question

Please bear with me on this as I’m new to this.

I have an array and two threads.

First thread appends new elements to the array when required

myArray ~= newArray;

Second thread removes elements from the array when required:

extractedArray = myArray[0..10];
myArray = myArray[10..myArray.length()];

Is this thread safe?
What happens when the two threads interact on the array at the exact same time?

Answer 1

this is not thread safe

this has the classic lost update race:

appending means examening the array to see if it can expand in-place, if not it needs to make a (O(n) time) copy while the copy is busy the other thread can slice of a piece and when the copy is done that piece will return

you should look into using a linked list implementation which are easier to make thread safe

Java’s ConcurrentLinkedQueue uses the list described here for it’s implementation and you can implement it with the core.atomic.cas() in the standard library