Chapter 4 Operating Sys

Question 1

What is a thread?

Answer 1

• Each execution path within a process is called a
  thread.
• Every process has at least one thread of
  execution

Question 2

Process vs. Threads

Answer 2

Threads are the entities within a process
scheduled for execution on the CPU.

Every process has exactly one
program and every running program has at
least one thread of execution.

Question 3

True or False:

Answer 3

• Every process must have 1 or more programs.
• A process may only have 1 thread of execution.
• A thread may contain multiple programs.
• If one thread blocks, a process may continue
  running other threads in its program

Question 4

What is multithreaded?

Answer 4

Multithreaded processes are executed similarly to
multiprogramming of processes: the CPU is switched rapidly among the threads creating the illusion of parallel execution.

Question 5

Possible Thread Transition?

Answer 5

1. Thread blocks for input
2. Scheduler picks another thread
3. Scheduler picks this thread
4. Thread becomes able to run
   again

Question 6

pthread_create()

Answer 6

A new thread is created using the POSIX
pthread_create() call. The call to create specifies
the name of the procedure for the new thread to
run.

Question 7

pthread_exit()

Answer 7

When a thread has finished the work it has been
assigned, it can terminate by calling
pthread_exit(). This call stops the thread and
releases its stack.

Question 8

pthread_join()

Answer 8

Often a thread needs to wait for another thread
to finish its work and exit before continuing. The
thread that is waiting calls pthread_join() to wait
for a specific other thread to terminate.

Question 9

pthread_yield()

Answer 9

If a thread wishes to relinquish its CPU time to allow
another thread to run, it can call pthread_yield().
No similar mechanism exists for processes. It is
assumed that processes “compete” for CPU time.
Threads, on the other hand, work in cooperation
with each other within a specific process. Therefore,
relinquishing the CPU to a sibling thread may be
advantageous to the process as a whole.