We have studied locks and test$-$and$-$set. We have also studied semaphores and condition variables as well as some implementation for various classical problems such as producer$-$consumer and readers$-$writers. Now you are developing a multi$-$threaded database system that requires efficient synchronization mechanisms for managing queries to shared data records.

a$.$ Which one is the best?

Choice $1$ of $4$:condition variables

Choice $2$ of $4$:test$-$and$-$set

Choice $3$ of $4$:lock

Choice $4$ of $4$:semaphores