nitzan-haim / os_ex2 Goto Github PK

shahaf.hermann, iporat08
Shahaf Hermann (308156983), Ido Porat (307905166)
EX: 2

FILES:
uthreads.cpp -- The threads manager
Thread.h -- A thread class header file
Thread.cpp -- A thread class implementation
Makefile -- self explanatory
README -- you should read this

REMARKS:
NULL

ANSWERS:

1. A program computing many and multiple complex mathematical calculations, that might take a very long time, 
   as well as a few other easier calculations that would normally take a fraction of a second.
   In this case user-level threads would make a lot of sense since the easy calculations wouldn't 
   have to wait for the heavier ones to complete. It's also better than kernel-level threads since there are
   no system calls, so we don't have the related overhead.
2. Advantages: In one word - Isolation.
	       Each process (and therefore each tab) has a separately allocated memory, hence providing more 
               resistance to crashes and stability - if one tab crashes (due to an illegal memory access for example),
               the rest of the tabs should be unaffected, in contrast with thread usage where a thread crashing would 
	       crash the whole process (due to lack of isolation). Furthermore, inter-process communication
	       requires OS interference and hence making each tab more secure.
   Disadvantages: Higher overhead: Creating and terminating processes is significantly slower (by up to 100 times) 
		  than creating and terminating threads.
3. Firstly when typing in the command, an interrupt is sent from the keyboard to the OS, which handles it by 
   sending a SIGINT signal to the process running the application. Next, the application translate the written command
   Of "kill pid" to the appropriate signal (which is SIGTERM / SIGKILL), sends it to the OS, which handles it by ordering
   The termination of the requested process with id pid (using SIGKILL).
4. Real time = Actual time passed.
   Virtual time = actual running time of the process (time passed while process ran by the CPU).
   Real time measurement can be used for an alarm clock for example, and Virtual time measurement could be used to measure 
   a thread's life cycle (as done in this exercise).