Is a lock necessary in this situation?
c#, locking, multithreading
Solution
Being atomic is rarely enough.
I generally want to get the latest value for a variable, rather than potentially see a stale one - so some sort of memory barrier is required, both for reading and writing. A lock is a simple way to get this right, at the cost of potentially losing some performance due to contention.
I used to believe that making the variable volatile would be enough in this situation. I'm no longer convinced this is the case. Basically I now try to avoid writing lock-free code when shared data is involved, unless I'm able to use building blocks written by people who really understand these things (e.g. Joe Duffy).
Problem
Is it necessary to protect access to a single variable of a reference type in a multi-threaded application? I currently lock that variable like this: ``` private readonly object _lock = new object(); private MyType _value; public MyType Value { get { lock (_lock) return _value; } set { lock (_lock) _value = value; } } ``` But I'm wondering if this is really necessary? Isn't assignment of a value to a field atomic? Can anything go wrong if I don't lock in this case? P.S.: MyType is an immutable class: all the fields are set in the constructor and don't change. To change something, a new instance is created and assigned to the variable above.