Embed a thread safe ArrayList in Java by locking

Question

I want to write a simple thread safe arraylist that supports:

add (), remove (int i), insert (int i), update (int i) and get (int i)

One simple implementation is to add a lock to the internal data structure (for example, an array of objects), but this is not enough because only one thread could access the list at a time.

So my initial plan was to add a lock to each data slot, so that different threads can simultaneously access elements in different indexes. The data structure will look like this:

class MyArrayList {
    Lock listlock;
    Lock[] locks;
    Object[] array;
}

The lock should work as follows if there is no need to resize ():

• for get (int i), the thread must get locks [i].
• to insert (int i) the thread must get all the locks [j] for j> = i and listlock.
• to delete (int i), the thread must get all the locks [j] for j> = i and listlock.
• for add (), the stream should receive listlock.
• for insert (), the thread must get locks [i].

My questions:

• How to handle locks when resizing when adding more objects, and I need to create a new larger array to store all objects. This is annoying because some other threads may also wait for the locks to be released,
• Any best suggestions for introducing such a thread safe arraylist?

Answer 1

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