solidityPrevent reentrancy attacks

bool internal locked;
modifier noReentrancy() {
    require(!locked, "No reentrancy!"); locked = true; _; locked = false;
}ctrl + cgithub

`bool internal locked;` An internal variable with the current contract state needs to be defined	`modifier noReentrancy()` A modifier is created so that it can be easily appended to functions
`require(!locked, "No reentrancy!");` When a function with this modifier is executed, it checks if the contract is locked. If it is, it reverts execution.	`locked = true; _; locked = false;` The contract is locked, the function called is ran, and after execution the contract is unlocked.

Usage example

pragma solidity >=0.7.0 <0.9.0;

contract Reenctancy {

    uint256 public number;

    bool internal locked;
    modifier noReentrancy() {
        require(!locked, "No reentrancy!"); locked = true; _; locked = false;
    }

    function store(uint256 num) public noReentrancy(){
        number = num;
    }
}

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