Mutex Locking Mechanism

A mutex or mutual exclusion lock is a programming tool used to ensure that only one process can access a shared resource at a time. In smart contracts, this is implemented as a modifier that sets a boolean flag when a function starts and resets it when it ends.

If another call attempts to enter the function while the flag is set, the contract rejects the transaction. This is a powerful defense against reentrancy, as it prevents nested calls from modifying state variables.

While effective, it must be used carefully to avoid accidental deadlocks or excessive gas costs. It serves as a physical barrier within the code to enforce sequential execution.