It’s important to understand that there are two aspects to thread safety. execution control, and memory visibility The first has to do with controlling when code executes (including the order in which instructions are executed) and whether it can execute concurrently, and the second to do with when the effects in memory of what has … Read more
You are specifically asking about how they internally work, so here you are: No synchronization private int counter; public int getNextUniqueIndex() { return counter++; } It basically reads value from memory, increments it and puts back to memory. This works in single thread but nowadays, in the era of multi-core, multi-CPU, multi-level caches it won’t … Read more
Consider this code, int some_int = 100; while(some_int == 100) { //your code } When this program gets compiled, the compiler may optimize this code, if it finds that the program never ever makes any attempt to change the value of some_int, so it may be tempted to optimize the while loop by changing it … Read more
volatile tells the compiler not to optimize anything that has to do with the volatile variable. There are at least three common reasons to use it, all involving situations where the value of the variable can change without action from the visible code: When you interface with hardware that changes the value itself; when there’s … 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
volatile has semantics for memory visibility. Basically, the value of a volatile field becomes visible to all readers (other threads in particular) after a write operation completes on it. Without volatile, readers could see some non-updated value. To answer your question: Yes, I use a volatile variable to control whether some code continues a loop. … Read more