Q:- What are Interlocked functions? Are Interlocked functions faster than a lock around equivalent expression? Answer:- Interlocked class provides a set of static functions which allow a few simple operations to be performed thread safe. Apart from convenience, these functions are much faster than having a lock around an equivalent statement (explained below). First, following is a list of Interlocked functions with explanation in comments. long counter = 0; //Increment counter by 1 Interlocked.Increment (ref counter); //Decrement counter by 1 Interlocked.Decrement (ref counter); //Add 10 to counter Interlocked.Add (ref counter, 10); //Set counter = 100 and return the original value of counter before it was changed. //This usually does not require a lock but consider a scenario where //counter is a 64 bit value and code running on a 32 bit machine. //In such a scenario the assignment happens in 2 steps for each 32 bit part //and hence the assignment is not atomic. var oldCounterValue = Interlocked.Exchange (ref counter, 100); // Read a 64-bit value atomically into another variable (val) var val = Interlocked.Read(ref counter); // Set counter = 999 if counter == 1000 Interlocked.CompareExchange(ref counter, 999, 1000); As I mentioned these statements are faster in most cases and especially on modern CPUs, as these functions execute in a lock free manner or as a single instruction wherever possible, thus avoiding the need for a lock (they do use memory barriers though, to avoid reordering issues etc.) For example CompareExchange function uses the cpu instruction CMPXCHG which allows Comparison and Exchange of values in a single instruction which cannot be pre-empted.
Posted on: Tue, 23 Dec 2014 08:25:54 +0000
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