-
Notifications
You must be signed in to change notification settings - Fork 20
/
ser334_opt_module_osc7_sample_problems.lyx
2198 lines (1573 loc) · 36.7 KB
/
ser334_opt_module_osc7_sample_problems.lyx
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
#LyX 2.3 created this file. For more info see http://www.lyx.org/
\lyxformat 544
\begin_document
\begin_header
\save_transient_properties true
\origin unavailable
\textclass article
\use_default_options true
\maintain_unincluded_children false
\language english
\language_package default
\inputencoding auto
\fontencoding global
\font_roman "default" "default"
\font_sans "default" "default"
\font_typewriter "default" "default"
\font_math "auto" "auto"
\font_default_family default
\use_non_tex_fonts false
\font_sc false
\font_osf false
\font_sf_scale 100 100
\font_tt_scale 100 100
\use_microtype false
\use_dash_ligatures true
\graphics default
\default_output_format default
\output_sync 0
\bibtex_command default
\index_command default
\paperfontsize default
\spacing single
\use_hyperref false
\papersize default
\use_geometry true
\use_package amsmath 1
\use_package amssymb 1
\use_package cancel 1
\use_package esint 1
\use_package mathdots 1
\use_package mathtools 1
\use_package mhchem 1
\use_package stackrel 1
\use_package stmaryrd 1
\use_package undertilde 1
\cite_engine basic
\cite_engine_type default
\biblio_style plain
\use_bibtopic false
\use_indices false
\paperorientation portrait
\suppress_date false
\justification true
\use_refstyle 1
\use_minted 0
\branch dev
\selected 0
\filename_suffix 0
\color #faf0e6
\end_branch
\branch soln
\selected 0
\filename_suffix 0
\color #faf0e6
\end_branch
\branch blank
\selected 1
\filename_suffix 0
\color #faf0e6
\end_branch
\index Index
\shortcut idx
\color #008000
\end_index
\leftmargin 2.54cm
\topmargin 2.54cm
\rightmargin 2.54cm
\bottommargin 2.54cm
\secnumdepth 3
\tocdepth 3
\paragraph_separation indent
\paragraph_indentation default
\is_math_indent 0
\math_numbering_side default
\quotes_style english
\dynamic_quotes 0
\papercolumns 1
\papersides 1
\paperpagestyle default
\tracking_changes false
\output_changes false
\html_math_output 0
\html_css_as_file 0
\html_be_strict false
\end_header
\begin_body
\begin_layout Standard
\noindent
Arizona State University
\begin_inset space \hfill{}
\end_inset
SER334: Operating Systems & Networks
\end_layout
\begin_layout Standard
\noindent
UGTA Lisonbee (6), Lecturer Acuña (4)
\begin_inset space \hfill{}
\end_inset
Revised 1/1/2019
\end_layout
\begin_layout Standard
\noindent
\begin_inset CommandInset line
LatexCommand rule
offset "0.5ex"
width "100col%"
height "1pt"
\end_inset
\end_layout
\begin_layout Standard
\size huge
Sample Problems - Deadlocks
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\size huge
(SOLN)
\end_layout
\end_inset
\end_layout
\begin_layout Standard
\begin_inset VSpace bigskip
\end_inset
\end_layout
\begin_layout Standard
\begin_inset Formula $ $
\end_inset
\end_layout
\begin_layout Standard
In this exercise, we will review the ideas of Deadlocks.
\end_layout
\begin_layout Itemize
Length: 50 minutes with discussion.
\end_layout
\begin_layout Itemize
Questions: Q2, Q4-Q7 (optional: Q1, Q3, Q8-Q10)
\end_layout
\begin_layout Standard
\begin_inset Branch dev
inverted 0
status open
\begin_layout Itemize
Describe resource usage in terms of request, use, and release.
Q
\begin_inset CommandInset ref
LatexCommand ref
reference "determine-request-use-release"
plural "false"
caps "false"
noprefix "false"
\end_inset
\end_layout
\begin_layout Itemize
Describe the concept of a deadlock.
\end_layout
\begin_layout Itemize
Describe the necessary conditions for a deadlock to occur.
\end_layout
\begin_layout Itemize
S2: Explain the meaning of the graphical notation in a resource allocation
graph.
Q
\begin_inset CommandInset ref
LatexCommand ref
reference "enu:rag-notation-read"
\end_inset
\end_layout
\begin_layout Itemize
S2: Identify deadlocks in a resource allocation graph notation.
Q
\begin_inset CommandInset ref
LatexCommand ref
reference "enu:rag-notation-read"
\end_inset
\end_layout
\begin_layout Itemize
S7: Select what would be the best deadlock recovery method to resolve a
deadlock scenario.
Q
\begin_inset CommandInset ref
LatexCommand ref
reference "determine-deadlock-method"
plural "false"
caps "false"
noprefix "false"
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Section
System Model
\end_layout
\begin_layout Enumerate
[Lisonbee] Three processes are run at the same time, and all use the same
resource (of which there is only one instance).
Each process will always only use the resource for 5 units of time.
How will the request and release times look respective to the order in
which the processes request, use, and release the resource?
\series bold
Explain.
\series default
[2 points]
\begin_inset CommandInset label
LatexCommand label
name "determine-request-use-release"
\end_inset
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 4cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status open
\begin_layout Standard
\series bold
Ans: [Lisonbee]
\end_layout
\begin_layout Standard
As there is only one instance of the resource, only one process will be
able to aquire it at first.
This means that the request time for the first process will be 0, but the
request time for the second process will be equal to the release time of
the first (5).
As follows, the third process's request time will be equal to the release
time of the second process (10).
The third process will then release after it uses the resources for 5 more
units of time (15).
\begin_inset VSpace 0.75cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
[Lisonbee] A system has a printer and a CD drive (two resource types, each
with one instance available), and two processes that are running.
The first process requests the CD drive resource and the second process
requests the printer resource.
Each is able to acquire the first resource it requests since it is available.
Both processes require both the printer and the CD drive in order to complete
their work, printing a file from the disk, so they each request the second
resource they need.
Is this system in a deadlock after the second request? If so,
\series bold
explain
\series default
which processes and/or resources are deadlocked.
If not,
\series bold
explain
\series default
the order in which the processes request, use, and release the resources.
[2 points]
\begin_inset Note Note
status collapsed
\begin_layout Enumerate
TODO: given a scenario, identify if there is a deadlock and if so what is
deadlocked (process and resource).
doesn't have to OS based, can do real world scenario
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 4cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans: [Lisonbee]
\end_layout
\begin_layout Standard
Yes, the system would be in a deadlock.
Each process aquires one of the two resources, and they will both be stuck
waiting for the other resource they need as the other process has it.
Each of the two processes and each instance of the two resources are deadlocked
as both processes are waiting for the opposite resource.
\end_layout
\begin_layout Standard
\begin_inset VSpace 0.75cm
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Section
Deadlock Characterization
\end_layout
\end_deeper
\begin_layout Enumerate
[Lisonbee] Given a situation where multiple processes all request to write
to the same file simultaneously (but only one processes can have write
access at a time), what deadlock condition will most likely occur?
\series bold
Explain.
\series default
[2 points]
\begin_inset Note Note
status collapsed
\begin_layout Enumerate
TODO: give a scenario and ask which of the deadlock conditions might occur
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 4cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status open
\begin_layout Standard
\series bold
Ans: [Lisonbee]
\end_layout
\begin_layout Standard
Mutual exclusion.
The definition states that for this condition to be valid a resource can
only be held by one process at a time, and only after the process releases
the resource may another process acquire it.
It wouldn't be hold and wait because it is never mentioned that there is
another resource that the processes are waiting for.
It also wouldn't be no preemption because there isn't enough information
given about this particular system.
Furthermore, it wouldn't be circular wait because that would again imply
that there is more than one resource, which there isn't in this case.
\end_layout
\begin_layout Standard
\begin_inset VSpace 1cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
[Acuña] Considering the following resource allocation graph, and answer
the following questions:
\begin_inset CommandInset label
LatexCommand label
name "enu:rag-notation-read"
\end_inset
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Graphics
filename opt_module_osc7/exe/ser334_unit8_exercise_sample_simple_rag.png
scale 40
\end_inset
\end_layout
\begin_layout Enumerate
[Acuña] How many resources are there in this graph? (Hint: this is a trick
question, the answer is not a number.)
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 3cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans: [Acuña]
\end_layout
\begin_layout Standard
Can't tell! In order to give an answer need to know if we are talking about
resource types (5) or resource instances (9).
\end_layout
\begin_layout Standard
\begin_inset VSpace 1cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
[Acuña] What resource type is needed by the most processes?
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 3cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans: [Acuña]
\end_layout
\begin_layout Standard
R0
\end_layout
\begin_layout Standard
\begin_inset VSpace 1.25cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
[Acuña] Does the graph above contain a deadlock?
\series bold
Explain.
\series default
[1 point]
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 3cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans: [Acuña]
\end_layout
\begin_layout Standard
No, there are no cycles without free resources available.
\end_layout
\begin_layout Standard
\begin_inset VSpace 1.25cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
[Acuña] What
\series bold
edges
\series default
would you need to introduce in the graph to create a deadlock between P0
and P1? [2 points]
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 3cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans: [Acuña]
\end_layout
\begin_layout Standard
P1 would need to acquire a second instance of R1, and request R4.
\end_layout
\begin_layout Standard
\begin_inset VSpace 1.25cm
\end_inset
\end_layout
\end_inset
\end_layout
\end_deeper
\begin_layout Section
Methods for Handling Deadlocks
\end_layout
\end_deeper
\begin_layout Enumerate
[Lisonbee] A mission critical system is a system that needs to have 100%
up time (like a life-support system or a nuclear reactor controller).
For this kind of system, does it make more sense to employ the use of a
prevention or recovery method of handling deadlocks in the case that they
occur?
\series bold
Explain.
\series default
[2 points]
\begin_inset CommandInset label
LatexCommand label
name "determine-deadlock-method"
\end_inset
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 4cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status open
\begin_layout Standard
\series bold
Ans: [Lisonbee]
\end_layout
\begin_layout Standard
Prevention would be the necessary way to handle deadlocks in this kind of
system.
It means that the system will be guarenteed to never encounter a deadlock,
and thus never be in a situation where the system needs to be restarted/recover
ed.
Recovery would give better performance but in this case that isn't important.
\end_layout
\begin_layout Standard
\begin_inset VSpace 1cm
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Section
Deadlock Prevention
\end_layout
\end_deeper
\begin_layout Enumerate
[Lisonbee] In your OS of choice, explain how you could implement a prevention
method for deadlocks that would ensure that circular wait can never occur
in the system.
\series bold
Explain
\series default
your answer in terms of the system's processes and resources, and how they
interact to avoid circular wait.
[2 points]
\begin_inset Note Note
status open
\begin_layout Enumerate
TODO: ask them how to implement one of the prevention techniques in an OS.
(can give scenario if they need it to narrow down an answer)
\end_layout
\end_inset
\end_layout
\begin_deeper
\begin_layout Standard
\begin_inset Branch blank
inverted 0
status collapsed
\begin_layout Standard
\begin_inset VSpace 4cm
\end_inset
\end_layout
\end_inset
\begin_inset Branch soln
inverted 0
status collapsed
\begin_layout Standard
\series bold
Ans: [Lisonbee, Silberschatz]
\end_layout
\begin_layout Standard
Circular wait can be avoided by assigning each resource a unique number
that identifies it.
By ensuring that processes can only aquire resources in ascending order
of their identifying number, circular wait is guarenteed to never occur.
\end_layout
\begin_layout Standard
\begin_inset VSpace 1cm
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Standard
\begin_inset Newpage pagebreak
\end_inset
\end_layout
\end_deeper
\begin_layout Enumerate
[Silberschatz, Lisonbee] Consider the following C code:
\begin_inset listings
lstparams "language=C"
inline false
status open
\begin_layout Plain Layout
/* thread one runs in this function */
\end_layout
\begin_layout Plain Layout
void *do_work_one(void *param)
\end_layout
\begin_layout Plain Layout
{
\end_layout
\begin_layout Plain Layout
pthread_mutex_lock(&first_mutex);
\end_layout
\begin_layout Plain Layout
pthread_mutex_lock(&second_mutex);
\end_layout
\begin_layout Plain Layout
/**
\end_layout
\begin_layout Plain Layout
* Do some work
\end_layout
\begin_layout Plain Layout
*/
\end_layout
\begin_layout Plain Layout
pthread_mutex_unlock(&second_mutex);
\end_layout
\begin_layout Plain Layout
pthread_mutex_unlock(&first_mutex);
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
pthread exit(0);
\end_layout
\begin_layout Plain Layout
}
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
/* thread two runs in this function */
\end_layout
\begin_layout Plain Layout
void *do_work_two(void *param)
\end_layout
\begin_layout Plain Layout
{
\end_layout
\begin_layout Plain Layout
pthread_mutex_lock(&second_mutex);
\end_layout
\begin_layout Plain Layout
pthread_mutex_lock(&first_mutex);
\end_layout
\begin_layout Plain Layout
/**
\end_layout
\begin_layout Plain Layout
* Do some work
\end_layout
\begin_layout Plain Layout
*/
\end_layout
\begin_layout Plain Layout
pthread_mutex_unlock(&first_mutex);
\end_layout
\begin_layout Plain Layout
pthread_mutex_unlock(&second_mutex);
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout
pthread exit(0);
\end_layout
\begin_layout Plain Layout
}
\end_layout
\end_inset
Does this code run the chance of creating a deadlock when it is run? If
so, what is a potential way to fix the code so it cannot create a deadlock?