How to fix deadlock in a Wallets task? Can atomic operations be used?

A deadlock in a task with Wallets usually occurs when multiple locks are acquired simultaneously in different orders, for example, during a transfer of funds between wallets. To fix the deadlock, it is necessary to ensure a consistent order of lock acquisition. For example, always lock wallets in ascending order of their IDs.

Using atomic operations (atomics) is suitable if operations on the balance can be reduced to simple atomic increments/decrements without the need to lock multiple resources simultaneously. However, in the case of transferring between two wallets, atomics will not help, as it is necessary to ensure consistency between the two accounts.

An example of a solution with ordered lock acquisition:

synchronized (wallet1.getId() < wallet2.getId() ? wallet1 : wallet2) {
    synchronized (wallet1.getId() < wallet2.getId() ? wallet2 : wallet1) {
        // transfer funds
    }
}

Thus, the deadlock is eliminated by fixing the order of lock acquisition.