Depends on what you are working on? Cross-request cache's naturally require synchronization. Although you could simply get away with thread-local storage. In

Depends on what you are working on? Cross-request cache's naturally require synchronization. Although you could simply get away with thread-local storage. In huge systems, there's always some other thread doing stuff that you may be using in a way that hides the fact that it is thread-safe. I'm no expert, mind you. I avoid concurrency problems if possible, but they are sometimes unavoidable. I touch shared resources that would OOM if made thread-local.