Miscellenia

As-of-yet unorganized information from lecture.

Deadlock (?)

Example: Terminating a stuck process

Suppose we have a process that is infinitely looping.

To prevent a deadlock, the computer can set a timer to interrupt the computer after some time n.

Basically, have a counter decremented by the physical clock, and generate an interrupt if it hits 0.
- (The OS sets the counter via priviledged instruction)

Remember: One of the goals is to distribute resources equally.

We want system calls for stuff like

User Interface: Almost all OSes have a user interface (UI)

Program Execution: System must be able to load a program into memory, run that program, and end (normally or abnormally).

I/O: A running program may require I/O, which may involve a file or an I/O device.

File System Manipulation: Read/write, create/delete, ls, permissions.

Communication: Exchange info on same computer or between computers.

Error Detection: OS should take appropriate action to ensure corret and consistent computing

Functions for resource sharing.

Resource Sharing: When multiple users/jobs run concurrently.

Accounting: Keep track of which users use how much and what kinds of resources.

Protection and Security:

Command Interpreter: Allows direct command entry.

Example: Built-in and not built-in commands

Some commands may be implemented in the OS, translating straight into system calls.

write(...)
  # implementation here
read(...)
  # implementation here

(More popularly), we modularize the definition, and the OS only provides an interface.

write(...)
  # interface
read(...)
  # interface

You know what a GUI is.

TODO Add this to previous

System calls can be:

Typically a number is associated with each system call.

System-Call Interface:

Invokes intended system call in kernel and returns status and any return values.
Caller know nothing about implementation. Details are hidden.
Caller only needs to obey API.