interview Question regarding less expensive type of locking in C#

[sbakoola]

I got a recent interview Question regarding less expensive type of locking in C#, I described a singleton and they asked my about threading issues, I stated that because the singleton had a single static instance I would have to use lock(someref) for the get property which returns it singleton instance. They then told me that doing a lock on every get would be expensive so what would be a cheaper alternative to locking on the get instance property for the singleton class.]

Anyone know ?

[VectraMan]

Re: interview Question regarding less expensive type of locking in C#

I don't know how you do it in C# specifically, but what you want is some kind of atomic test and set. With a singelton, only the first call actually has to do anything, every other call just returns a static variable, so a lock is an unnecessary overhead.

Though what might be better is to initial
ise your singeltons at startup.

[jmo21]

Probably more than you need to know about singleton and locking in C#.

Linky

[AtW]

Offtopic, but very interesting new stuff in Intel's Haswell - hopefully C# and other languages include support very quickly -

AnandTech - Making Sense of the Intel Haswell Transactional Synchronization eXtensions

[centurian]

Double checked locking

In most cases for a singleton, the value is set after the first few calls (very often in the first call), so performing a lock on every subsequent call is unneccessary. This can be handled with an extra if statement and if it does need to be set, then go into a lock statement and restest inside the lock statement.