Is it possible transaction A get executed while transaction B is in middle of execution in the same block?

Question

Imagine I have deposit function which can receive funds from user and the amount sent will be updated in state based on balanceBefore and balanceAfter of token in the contract:

1:    function deposit(IERC20 token, uint256 amount) public{
2:        uint256 balanceBefore = token.balanceOf(address(this));
3:
4:       token.transferFrom(msg.sender,address(this),amount);
5:
6:        uint256 balanceAfter = token.balanceOf(address(this));
7:        
8:        balance[msg.sender] = balanceAfter - balanceBefore;
9:    }

now lets say user A calls deposit and in same time user B calls deposit but user's B transaction will be mined when user's A transaction is in middle of execution(in proccesing after line 3) so user B has sent token to contract and contract's balance is increased. In such a scenario user's A balance will be updated more than expected.

Is it possible this scenario happen? if yes is it based on luck?

Answer 1

Transactions are executed sequentially in the block, there is no overlap. The scenario you describe can never happen.