1. Visibility
2. Access Problems
Difficulty of writing code. Multithreaded and multicontexted applications are not easy to write. ...
Difficulty of debugging. ...
Difficulty of managing concurrency. ...
Difficulty of testing. ...
Difficulty of porting existing code.
https://docs.oracle.com/cd/E13203_01/tuxedo/tux71/html/pgthr5.htm