How does compressed oops behave in multithreaded code?

Compressed Object Pointers (oops) in Java are used to reduce the memory footprint of object references in a 64-bit JVM. When using compressed oops, object references are 32-bit instead of 64-bit, allowing for more efficient memory utilization. This can lead to improved performance, especially in applications that manage a large number of objects.

In a multithreaded environment, compressed oops can behave differently compared to a single-threaded scenario. Each thread can still access shared object references, but care must be taken to ensure that all threads are aware of the reference's compressed state. The JVM handles this in a way that is mostly transparent to developers, but understanding the implications is crucial for optimizing performance.

For example, if multiple threads are accessing and modifying a shared data structure, using compressed oops can reduce the overhead of managing larger object references, leading to better cache performance and reduced contention among threads.