Requirement of process relative handles

Question

What is the requirement of process relative handles?

Answer 1

The most significant reason was robustness. If kernel object handles were system-wide values, one process could simply obtain the handle to an object that another process was employing and wreak havoc on that process. Another cause for process-relative handles is security. Kernel objects are protected with security, and a process has to request permission to manipulate an object before trying to manipulate it. The creator of the object can prevent an unauthorized user from touching the object just by denying access to it.