Others have addressed the “why?”. It is easy however to roll your own Add(ref double, double), using the CompareExchange primitive: public static double Add(ref double location1, double value) { double newCurrentValue = location1; // non-volatile read, so may be stale while (true) { double currentValue = newCurrentValue; double newValue = currentValue + value; newCurrentValue = … Read more
x86 does not require alignment for a lock cmpxchg instruction to be atomic. However, alignment is necessary for good performance. This should be no surprise, backward compatibility means that software written with a manual from 14 years ago will still run on today’s processors. Modern CPUs even have a performance counter specifically for split-lock detection … Read more
This is thread safe, right? Suppose MAXIMUM is one, count is zero, and five threads call CheckForWork. All five threads could verify that count is less than MAXIMUM. The counter would then be bumped up to five and five jobs would start. That seems contrary to the intention of the code. Moreover: the field is … Read more
I’m a firm believer in that if you’re using interlocked to increment shared data, then you should use interlocked everywhere you access that shared data. Likewise, if you use insert you favorite synchronization primitive here to increment shared data, then you should use insert you favorite synchronization primitive here everywhere you access that shared data. … Read more
Worst (won’t actually work) Change the access modifier of counter to public volatile As other people have mentioned, this on its own isn’t actually safe at all. The point of volatile is that multiple threads running on multiple CPUs can and will cache data and re-order instructions. If it is not volatile, and CPU A … Read more