Problems with Thread Local Variables
- They are mutable, which means any code with access to them can change them. This can make it difficult to understand and debug your application.
- They have an infinite lifetime, which means they will remain in memory until the thread is killed unless you manually remove them. Memory leaks are possible if they are not removed or if multiple threads inherit them from their parent threads.
- Because they are expensive to inherit, each child thread must allocate memory for each thread-local variable set by its parent thread. This can add a lot of expense when there are a lot of threads.
Scoped Values in Java
In Java, Scoped variables enable the exchange of immutable data across and between threads. This new API is implemented as an incubator preview feature in Java 20 as part of JEP 439. They are preferred over thread-local variables, especially when a large number of virtual threads are used. This is an API that is still in development.
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