Mutex Locking in Solidity

Mutex locking in Solidity is a technique used to restrict access to a function so that it cannot be called again until the previous execution has finished. This is typically implemented using a boolean flag that is set to true at the start of a function and reset to false at the end.

This simple lock prevents reentrancy by blocking any subsequent attempts to enter the function during the same transaction. While effective, it must be implemented carefully to ensure that the lock is always released, even if the transaction reverts.

If a lock is left in the 'true' state, it could permanently block access to the function, rendering the contract unusable. It serves as a secondary defense alongside the checks-effects-interactions pattern.