Almost zero. Queues or streams may have lockless properties. Or maybe not! For the most part concurrent, mutable access to a shared data structure is undesira

Almost zero. Queues or streams may have lockless properties. Or maybe not! For the most part concurrent, mutable access to a shared data structure is undesirable and to be avoided. If you find yourself wanting a lockless hashmap you’re going down the wrong path 99.9% of the time. There are always exceptions. But you better have a REALLY good reason why.