Choices

In the Choices operating system [11, ] so called agents can be inserted into the kernel. Agents are written in a simple, flexible scripting language similar to TCL, and are interpreted. Agents batch a series of system calls into a single procedure that requires only one trap into the kernel to be executed. Agents use existing kernel services and do not extend the functionality of the kernel or provide services that are not available at user level. Agents are a simple optimizations to eliminate the overhead of several system calls.

Methods to safely execute untrusted code in a privileged environment are compared in [86]. Among the methods chosen is interpreted TCL because of its mention in the Choices papers. As might be expected, TCL's execution speed is orders of magnitudes slower than some of the other methods. Therefore, the authors claim that interpretation in general is too slow. However, TCL interpreters are not optimized for speed. Furthermore, with appropriate restrictions to the language and application of advanced interpretation techniques, it might be possible to speed-up interpretation considerably.