To Mutex or Not To Mutex?

Question

Do I need a mutex if I have only one reader and one writer? The reader takes the next command (food.front()) from the queue and executes a task based on the com

Answer 1

Depends entirely on the implementation, if you have two different threads accessing the same variables you will need a mutex. Otherwise you may for example end up with an inconsistent count.

Say in write you do ++count and in read you do --count and say the current value is 2. Now note that these statements do not need to be atomic, the ++count may consist of reading variable count, incrementing it and then writing it back again. No a write and read are simultaneously executed and say the first bit of the write is executed is executed (i.e. it loads value 2. then the whole read is executed decrementing the count, but the other thread still had value 2 loaded, which it increments and subsequently writes back to the variable. Now you just lost a read action.