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| DATE | 2015-03-16 |
| FROM | mrbrklyn@panix.com
|
| SUBJECT | Subject: [LIU Comp Sci] Operating Systems Chapter 3 HW complete
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From: mrbrklyn-at-panix.com
To: learn-at-nylxs.com
Subject: [LIU Comp Sci] Operating Systems Chapter 3 HW complete
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This is all of the chapter 3 question and one programming project.
I wanted to do more of the programming projects but I've been busy
working on a virtual server and testing custom kernel compiles for
our scheduler project, which I wanted just finish and get off my
plate. The Kernel is so large now and difficult to set up the
config file that is takes more time. It doesn't help to have
hostile developers now who think users aren't supposed to ask
about kernel internals. This makes me fustrated. When did it
happen that asking to compile a kernel is offensive to distribution
developers and that development tools became exclussive property
of the few??
Umbuntu, and the Umbuntu attitude really is crushing the Linux community.
Ruben
--
So many immigrant groups have swept through our town
that Brooklyn, like Atlantis, reaches mythological
proportions in the mind of the world - RI Safir 1998
http://www.mrbrklyn.com
DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002
http://www.nylxs.com - Leadership Development in Free Software
http://www2.mrbrklyn.com/resources - Unpublished Archive
http://www.coinhangout.com - coins!
http://www.brooklyn-living.com
Being so tracked is for FARM ANIMALS and and extermination camps,
but incompatible with living as a free human being. -RI Safir 2013
--17pEHd4RhPHOinZp
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Practice Exercises
3.1
Using the program shown in Figure 3.30, explain what the output will
be at LINE A.
Answer: A is 5
#include
#include
#include
int value = 5;
int main()
{
pid t pid;
pid = fork();
if (pid == 0) { /* child process */
value += 15;
return 0;
}
else if (pid > 0) { /* parent process */
wait(NULL);
printf("PARENT: value = %d",value); /* LINE A */
return 0;
}
}
3.2
Including the initial parent process, how many processes are created by
the program shown in Figure 3.31?
Answer:
Eight!!!
xterm???bash???a.out???a.out???a.out???a.out
? ? ??a.out
? ??a.out???a.out
? ??a.out
#include#include
int main()
{
/* fork a child process */
fork();
/* fork another child process */
fork();
/* and fork another */
fork();
return 0;
}
Figure 3.31 How many processes are created?
3.3
Original versions of Apple’s mobile iOS operating system provided no
means of concurrent processing. Discuss three major complications that
concurrent processing adds to an operating system.
Answer: memory requiements are larger with + multisourced oses,
longer wait times for i/o an ready cues since there
is a limited schedular without concurency, but the application that is
running reacts faster since there is no CPU overhead for short term scheduling.
Few registers are needed on the CPU for quick concurancy contact swaps.
3.4
The Sun UltraSPARC processor has multiple register sets. Describe what
happens when a context switch occurs if the new context is already
loaded into one of the register sets.
Answer: On the hardware level, registers are just switched, and the
program counter just reset, rather than the entire context tossed on the stack.
What happens if the new context is
in memory rather than in a register set and all the register sets are in
use?
All the context has to be rebuilt off the stack a, and all the active
registers have to be reset to the saved condition.
3.5
When a process creates a new process using the fork() operation, which
of the following states is shared between the parent process and the child
process?
a. Stack
b. Heap
c. Shared memory segments
Answer: Share Memory segments.
3.6
Consider the “exactly once”semantic with respect to the RPC mechanism.
Does the algorithm for implementing this semantic execute correctly
even if the ACK message sent back to the client is lost due to a network
problem? Describe the sequence of messages, and discuss whether
“exactly once” is still preserved.
If a client demanding a RPC doesn't retreive the ACK under the exactly once
semantic, then it will time out and send another request to the server. Each
request as a time stamp, and when the server sees the duplicate, it will not
open another request, but send a new ack instead.
3.7
Assume that a distributed system is susceptible to server failure. What
mechanisms would be required to guarantee the “exactly once” semantic
for execution of RPCs?
What is he fishing for here? This was just explained.
3.8
Describe the differences among short-term, medium-term, and long-
term scheduling.
Short term Scheduling is the rotation of all processes on the ready cue
to get cpu time.
Long Term scheduling is used to balance types of process usage and to
keep resources management from running away.
medium-term scheduling will roll processes tepmorarily off of the ready
cue when cpu time is tied up, and load processes onto swap.
#include#include
int{
main()
int i;
Exercises
for (i = 0; i < 4; i++)
fork();
return 0;
}
Figure 3.32 How many processes are created?
3.9 Describe the actions taken by a kernel to context-switch between
processes.
When a context switch occurs, the kernel saves the context
of the old process in its PCB and loads the saved context of the new process
scheduled to run. Virtual address space might need to be saved as well
3.10 Construct a process tree similar to Figure 3.8. To obtain process infor-
mation for the UNIX or Linux system, use the command ps -ael.
[ruben-at-stat13 ~]$ pstree -Ap
init(1)-+-NetworkManager(2364)-+-dhclient(2509)
| |-{NetworkManager}(2365)
| |-{gdbus}(2377)
| `-{gmain}(2376)
|-acpid(2273)
|-agetty(2849)
|-agetty(2850)
|-agetty(2851)
|-agetty(2852)
|-agetty(2853)
|-agetty(2854)
|-at-spi-bus-laun(5511)-+-dbus-daemon(5515)
| |-{dconf worker}(5512)
| |-{gdbus}(5514)
| `-{gmain}(5516)
|-at-spi2-registr(5518)---{gdbus}(5520)
|-avahi-daemon(2610)---avahi-daemon(2611)
|-colord(2728)-+-{gdbus}(2730)
| `-{gmain}(2731)
|-console-kit-dae(2335)-+-{gdbus}(2360)
| |-{gmain}(2358)
| |-{vt_thread_start}(2355)
| `-{writer_thread_s}(2340)
|-crond(2588)
|-cupsd(2726)---{cupsd}(2734)
|-dbus-daemon(2314)
|-dbus-daemon(2986)
|-dbus-launch(2985)
|-dconf-service(5562)-+-{gdbus}(5564)
| `-{gmain}(5565)
|-gvfs-udisks2-vo(5420)-+-{gdbus}(5421)
| `-{gmain}(5422)
|-gvfsd(3013)---{gdbus}(3014)
|-gvfsd-cdda(5430)---{gdbus}(5431)
|-gvfsd-fuse(3017)-+-{gdbus}(3027)
| |-{gvfs-fuse-sub}(3028)
| |-{gvfsd-fuse}(3025)
| `-{gvfsd-fuse}(3026)
|-gvfsd-metadata(5537)---{gdbus}(5539)
|-gvim(3802)---{gdbus}(3803)
|-kactivitymanage(3139)-+-{QInotifyFileSys}(3146)
| |-{QThread}(3143)
| |-{QThread}(3144)
| |-{QThread}(3145)
| |-{QThread}(3147)
| `-{QThread}(5390)
|-kded4(3041)---{QInotifyFileSys}(3275)
|-kdeinit4(3037)---klauncher(3039)
|-knotify4(3271)---{QInotifyFileSys}(3272)
|-kuiserver(3701)
|-lxdm-binary(2544)-+-Xorg.bin(2587)---{Xorg.bin}(2732)
| `-lxdm-session(2882)---wmaker(2889)---wmaker(2988)-+-oclock(2992)
| |-xterm(2993)---bash(3004)---pstree(5869)
| |-xterm(2994)---bash(3003)
| |-xterm(3790)---bash(3792)
| |-xterm(4911)---bash(4913)---okular(5616)-+-{QI+
| | `-{QP+
| `-xterm(5394)---bash(5396)
|-metalog(2224)---metalog(2225)
|-ntpd(2781)
|-oclock(3000)
|-pidgin(2999)---{gdbus}(3011)
|-polkitd(2362)-+-{gdbus}(2378)
| |-{gmain}(2363)
| |-{polkitd}(2379)
| `-{runaway-killer-}(2380)
|-rsyslogd(2248)-+-{in:imklog}(2250)
| |-{in:imuxsock}(2249)
| `-{rs:main Q:Reg}(2251)
|-sshd(2804)
|-udevd(699)
|-udisksd(3093)-+-{cleanup}(3111)
| |-{gdbus}(3109)
| |-{gmain}(3107)
| `-{probing-thread}(3110)
|-upowerd(3048)-+-{gdbus}(3050)
| `-{gmain}(3049)
`-wicd(2408)---wicd-monitor(2478)
Use the command man ps to get more information about the ps com-
mand. The task manager on Windows systems does not provide the
parent process ID, but the process monitor tool, available from tech-
net.microsoft.com, provides a process-tree tool.
3.11 Explain the role of the init process on UNIX and Linux systems in regard
to process termination.
init is the system program that launches all the services that control the GNU/Linux
system. It is the root process and waits for all the child processes. Ultimately
it cleans zombie processes.
Its roll has been dramatically expanded and changed with the advent of
systemd, and no longer are the processes just spun off and waited for. Instead,
many core functions have been built directly into the init binary.
The initiation system for Linux has evolved over the years from a BSD proc system
to what was then called SySV and now we have systemd, or the competing openrc.
Emphasis on fail over and remote usage has pushed comercial vendors to a more
integrated approch in systemd at process 1.
3.12 Including the initial parent process, how many processes are created by
the program shown in Figure 3.32?
#include
#include
int main() {
int i;
for (i = 0; i < 4; i++)
fork();
return 0;
}
Figure 3.32
This is the same as before and creates 8 processes
P -> P2 -----> P3 -> P4
| |
P3 ->P4 P4
|
P4
3.13 Explain the circumstances under which which the line of code marked
printf("LINE J") in Figure 3.33 will be reached.
ANSWER: NONE
man execlp
The exec() family of functions replaces the current process image with
a new process image. The functions described in this manual page are
front-ends for execve(2). (See the manual page for execve(2) for fur?
ther details about the replacement of the current process image.)
#include
#include
#include
int main()
{
pid t pid;
/* fork a child process */
pid = fork();
if (pid < 0) { /* error occurred */
fprintf(stderr, "Fork Failed");
return 1;
}
else if (pid == 0) { /* child process */
execlp("/bin/ls","ls",NULL);
printf("LINE J");
}
else { /* parent process */
/* parent will wait for the child to complete */
wait(NULL);
printf("Child Complete");
}
}
3.14 Using the program in Figure 3.34, identify the values of pid at lines A, B,
C, and D. (Assume that the actual pids of the parent and child are 2600
and 2603, respectively.)
#include
#include
#include
int main()
{
pid_t pid, pid1;
/* fork a child process */
pid = fork();
if (pid < 0) { /* error occurred */
fprintf(stderr, "Fork Failed");
return 1;
}
else if (pid == 0) { /* child process */
pid1 = getpid();
printf("child: pid = %d",pid); /* A */
printf("child: pid1 = %d",pid1); /* B */
}
else { /* parent process */
pid1 = getpid();
printf("parent: pid = %d",pid); /* C */
printf("parent: pid1 = %d",pid1); /* D */
wait(NULL);
}
return 0;
}
A = 0
B = 2603
C = 2603
D = 2600
Figure 3.34 What are the pid values?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include
#include
#include
#define SIZE 5
int nums[SIZE] = {0,1,2,3,4};
int main()
{
int i;
pid t pid;
Exercises
pid = fork();
if (pid == 0) {
for (i = 0; i < SIZE; i++) {
nums[i] *= -i;
printf("CHILD: %d ",nums[i]); /* LINE X */
}
}
else if (pid > 0) {
wait(NULL);
for (i = 0; i < SIZE; i++)
printf("PARENT: %d ",nums[i]); /* LINE Y */
}
}
return 0;
Figure 3.35
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3.15 Give an example of a situation in which ordinary pipes are more suitable
than named pipes and an example of a situation in which named pipes
are more suitable than ordinary pipes.
One a services that has multiple child processes to talk to then ordinary pipes
are more useful. And example might be the Apache Web Server where multiple
children are spun off the parent and communication with the parent.
However, a named pipe is needed for any communication between two seperate
processes. It you need a music stream, for example, you be sent through a
service, you will need a named pipe for the streamer to talk to and the server
will have to read from the pipe.
3.16 Consider the RPC mechanism. Describe the undesirable consequences
that could arise from not enforcing either the “at most once” or “exactly
once” semantic. Describe possible uses for a mechanism that has neither
of these guarantees.
If timestamps are not compared and at most once of exactly once semantics are
not used then clients can not be assured that the data stream is correct
if they don't recieve a return message. The system is then fully dependent
of the physical perfection of the intrastructure for communication assurance.
3.17 Using the program shown in Figure 3.35, explain what the output will
be at lines X and Y.
Parent 0,1,2,3,4
Child 0,-1,-2,-3,-4
3.18 What are the benefits and the disadvantages of each of the following?
Consider both the system level and the programmer level.
a. Synchronous and asynchronous communication
Synchronous communications are slower and will cause latency problem but guantanty
communications with lower overhead as more communication is blocked until sending
matches recieving.
b. Automatic and explicit buffering
The text doesn't explain explicit buffering, but automatic buffering has
the advantage of having bound or infinite buffering space which allows
for lower message latency and few or no sender blocks.
I think the textbook maybe is messed up in this spot and needs rediting.
I would thing explicit buffering is any finetely defined buffering on the
communications que, which is GOOD and SECURE even though it requires sender blocks
INFINITE would be automatic and that is opimistic and NOT secure.
c. Send by copy and send by reference
Send by copy is a problem with MACH kernels because several copies of information is made.
It is essential for distributed systems but for smaller systems that share memory references
can lower the system overhead.
d. Fixed-sized and variable-sized messages
Fixed sized messages give certainty of buffer
needs and sizes and variable messages allow for greater
optimizations
Programming Problems
3.19 Using either a UNIX or a Linux system, write a C program that forks
a child process that ultimately becomes a zombie process. This zombie
process must remain in the system for at least 10 seconds. Process states
can be obtained from the command
ps -l
#include
#include
#include
#include
#include
int main( int argc, char * argv[]){
pid_t pid;
int i = 0;
puts("\nBefore the While Loop");
while( i++ < 100){
puts("\nBefore the Fork in the Loop:");
printf( "Loop ==> %d \n", i);
pid = fork();
puts("\nFork: This should print twice for every loop:");
if(pid < 0){
puts( "fork failed\n" );
return 1;
}
if(pid == 0) {
puts("\n\nChildren of the world unite");
printf("Am Yisrael Chai! pid =>%d \n", pid);
printf( "Loop in Child ==> %d \n", i);
puts("BYE!!");
exit( EXIT_SUCCESS );
}
if (pid > 0 ){
printf("In the Parent => I'm waiting %d\n", pid );
printf( "Loop in Parent ==> %d \n", i);
//wait(NULL);
puts("Done Waiting for Child");
}
}
return 0;
}
18456 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18457 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18458 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18459 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18460 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18461 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18462 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18463 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18464 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18465 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18466 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18467 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
18468 ruben 20 0 0.0m 0.0m 0.0 0.0 0:00.00 Z `- a.out
~~~~~~~~~~~~
--17pEHd4RhPHOinZp--
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