Exceptional Control Flow

Question 1

fork()

Answer 1

creates new process, that is exact copy of parent process. fork() returns 0 in the child, and returns the pid of the child to the parent.

fork() returns twice.

Question 2

Interrupts

Answer 2

interrupts occur asynchronously as a result of signals from IO devices that are external to the processor. they are not caused by a particular instruction.

return behavior: always returns to next instruction

Question 3

Trap

Answer 3

intentional exceptions that are caused by executing an instruction. Traps provide an interface between user programs and the Kernel (in the form of system calls).

Question 4

Examples of System calls

Answer 4

read (reading a file),
fork (creating a process),
execve (loading new program)
exit (terminating)

Question 5

Faults

Answer 5

Fault result from error conditions that a handler might ne able to correct. When a fault occurs the processor transfers control to a handler that may or may not be able to recover from the fault. if recovery is possible return to faulting instruction. else abort.

Question 6

Examples of Faults

Answer 6

page fault exception, Divide Error, General Protection Fault (seg-fault).

Question 7

Aborts

Answer 7

unrecoverable fatal errors. Eg. hardware error. Aborts to not return control to the program, but terminate.

Question 8

Def: Process

Answer 8

an instance of a running program

Question 9

Process Abstractions

Answer 9

1) logical control flow, each process things it is only program running.
2) private address space

Question 10

Process states

Answer 10

1) running
2) stopped, suspended and will not be scheduled until it get the signal todo so.
3) Terminated the process is stopped permanently. (terminated or returned from main, exited)

Question 11

Reaping Child Process

Answer 11

The processor returns the childs exit status to the parent.