In this blog post, that can be seen as a follow-up of my last post about acquire release semantics, I want to shine some light on getOpaque and setOpaque.

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Java's getOpaque and setOpaque methods provide program-order guarantees for operations on the same variable but no memory ordering effects between threads for different variables. Unlike volatile or acquire-release semantics, opaque mode allows reordering with operations on other variables, making it equivalent to C++ relaxed ordering. The post demonstrates through JCStress tests that opaque mode can observe out-of-order writes between different variables and shows unsafe behavior when publishing mutable object references. Valid use cases include broadcasting stop signals and progress updates, though volatile often remains the better choice due to clearer semantics and minimal performance differences.

What the Hell is GetOpaque in Java