Module 6

Question 1

Open file descriptor table

Answer 1

contains all the files that have been opened by a
process; stored in the PCB

Question 2

Page table

Answer 2

contains all the mappings from virtual to physical address space;
a pointer to the page table is stored in the process PCB

Question 3

Thread

Answer 3

created within a process; enables splitting an executing program into
multiple simultaneously or pseudo-simultaneously running tasks to keep the
CPU cores busy by having them run in parallel; each thread has its own
execution context, though the heap memory, static data segment, and code
segment of the virtual memory, as well as the open files, are shared with the
process

Question 4

Thread table

Answer 4

stores the execution context of the threads, which includes the
thread processor registers, stack pointer, program counter, MMU, general
registers, and stack memory segments

Question 5

Thread pool

Answer 5

where you pre-create a number of threads in the system, and
what you do is whenever a client comes in, you take one of the idle threads to
service the client; after the client request has been serviced, then the thread is
returned to the pool and it’s available for servicing future clients

Question 6

Thread affinity

Answer 6

CPU cores have caches and in multicore systems, if threads
keep getting run on the same core, then their data will be more likely to be
cached; thus, threads should always run on a specific core

Question 7

User level threads

Answer 7

the thread library is located in user space; the OS does is
not aware of the threads

Question 8

Kernel level threads

Answer 8

the thread library is located in kernel space; each
thread is handled and scheduled individually

Question 9

Virtual dynamic shared objects

Answer 9

allows user space to handle certain kernel
space routines, to reduce the need for context switching; memory allocated in
user space

Question 10

Concurrency control

Answer 10

managing the interleaved execution of multiple
processes that access the same shared states, to produce the correct results

Question 11

Race conditions

Answer 11

two or more threads or processes attempt to access and
update the same data at the same time; the result of a computation depends
on the exact timing of the multiple processes or threads being executed

Question 12

Synchronization

Answer 12

implementing coordination between processes
○ Critical section: a portion of code that involves an access or
modification of shared state
○ Mutual exclusion: enforcing that only one process is in any given
critical section at a time
○ Progress: if no process is currently in the critical section, and at least
one process wants to enter it, some process will eventually be able to
enter
○ Bounded waiting: a process that is waiting in line to enter the critical
section will not be waiting indefinitely, and is guaranteed to have an
opportunity to enter

Question 13

Busy-wait

Answer 13

a loop checking the same condition repeatedly; the process
busy-waiting cannot proceed until the condition becomes true; consumes
CPU resources inefficiently

Question 14

Disabling interrupts

Answer 14

an overly powerful approach to implementing
synchronization that prevents the OS from performing all context switches,
which are caused by interrupts

Question 15

Atomic statements

Answer 15

the compiler can translate such a statement to one line
of assembly language, thus making this an uninterruptible statement

Question 16

Deadlock

Answer 16

processes are waiting for each other, such that none of them can
proceed