Using any kind of thread local variable or mutex in the presence of nested tasking is problematic.

https://link.springer.com/chapter/10.1007/978-1-4842-4398-5_12

Taskflow doesn't currently provide any primitives to support task isolation.

In taskflow the equivalent nested task would cause a deadlock

tbb provides the task isolation primitives too assist with this. The attached article goes into more details and usecases.