Are primitive datatypes thread-safe in Java

There are three ways in which they’re not safe:

  • long and double aren’t even guaranteed to be updated atomically (you could see half of a write from a different thread)
  • The memory model doesn’t guarantee that you’ll see the latest updates from one thread in another thread, without extra memory barriers of some kind
  • The act of incrementing a variable isn’t atomic anyway

Use AtomicInteger etc for thread-safe operations.

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