03 03 Processes Part 3 — Transcript

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1. 0:08[Music]
2. 0:20all right
3. 0:22so next would be the multitasking in
4. 0:25mobile system
5. 0:27okay so let's talk about
6. 0:29an ios here so some mobile systems
7. 0:31example the early versions of ios
8. 0:34okay allow only one process to run and
9. 0:38then others are suspended so we look at
10. 0:40it as multitasking because multiple
11. 0:42processes are being executed but they
12. 0:45are not executed all at the same time
13. 0:48all right so that's what i said earlier
14. 0:50the concept here is that the cpu can
15. 0:52execute process one
16. 0:54one job at a time
17. 0:56okay or one process at a time
18. 0:59so due to screen real estate user
19. 1:01interface limits ios provides for a
20. 1:04single foreground process
21. 1:06controlled by uh user interface
22. 1:09and multiple background processors so
23. 1:11these are in the memory running but not
24. 1:14on the display and with its limits
25. 1:17okay
26. 1:18so for android
27. 1:20android runs foreground and background
28. 1:22with fewer limits so background
29. 1:24processes uses a service to perform
30. 1:26tasks
31. 1:28okay
32. 1:29while the service can keep running even
33. 1:31if the bracket process is suspended
34. 1:33so service has no user interface
35. 1:37and it uses only a small amount of
36. 1:39memory
37. 1:41okay
38. 1:44next
39. 1:45so operations under processes
40. 1:48so systems
41. 1:50must provide mechanism for
42. 1:52process creation and
43. 1:55process termination
44. 1:57okay
45. 1:58now let's talk about process creation
46. 1:59first
47. 2:01so in process creation there might be a
48. 2:03parent process
49. 2:05creating a child or children processes
50. 2:08which in turn
51. 2:10create other processes forming a tree of
52. 2:13processes
53. 2:14you've got the parent you've got the
54. 2:17root
55. 2:18and then you've got different branches
56. 2:20and then each branch has a tree or as a
57. 2:24leave
58. 2:24or leaf
59. 2:26okay
60. 2:27so
61. 2:28that forms a tree of a process
62. 2:31so generally
63. 2:32process identified and managed via
64. 2:35process identifier
65. 2:38so resource sharing options
66. 2:40is available so the parent and the
67. 2:42children
68. 2:44share all the resources
69. 2:46so we're talking about process and
70. 2:48thread relationships here
71. 2:50okay
72. 2:51so children share subset of the parent
73. 2:54resources
74. 2:55or the parent and child share no
75. 2:58resources at all
76. 2:59okay
77. 3:00now on the execution options so the
78. 3:03parent and children execute concurrently
79. 3:06all at the same time
80. 3:07okay so next would be the parent waits
81. 3:11until the children
82. 3:12terminate
83. 3:14can we terminate the parent without
84. 3:16terminating the children or the child
85. 3:18first the answer is no
86. 3:20okay
87. 3:21we have to ensure or the operating
88. 3:23system has to ensure that all the
89. 3:25children processes has ended before we
90. 3:27terminate
91. 3:29a parent
92. 3:33next process creation so the child
93. 3:36duplicate of parent
94. 3:39this is in terms of outer space and the
95. 3:42child has a program loaded into it
96. 3:44so in unix okay when you say fork
97. 3:48this is a system call
98. 3:51that creates a new process
99. 3:53okay so basically everything in an
100. 3:55operating system so if you want the
101. 3:57operating operating system to do
102. 3:59something you just have to issue a
103. 4:01system call
104. 4:02okay a system called to execute or to
105. 4:05create a new process
106. 4:07a system called to close the application
107. 4:09or terminate the applications so
108. 4:11basically everything in the operating
109. 4:13system is
110. 4:15in the principle of system calls
111. 4:18okay
112. 4:19and in unix
113. 4:21to create a new process
114. 4:23means fork
115. 4:26okay
116. 4:27exec
117. 4:28is a system called for
118. 4:30uh executing the program okay so after
119. 4:33the fork
120. 4:34so the process
121. 4:36is replaced
122. 4:37from the memory
123. 4:39space with a new program so we call it
124. 4:42exec
125. 4:42so the parent
126. 4:44process calls weight
127. 4:46waiting for the child to
128. 4:48terminate
129. 4:51all right
130. 4:54next so you've got a three of processes
131. 4:57in linux so we have mentioned about the
132. 4:59three of processes earlier okay
133. 5:02so
134. 5:03processes may create other process
135. 5:07through appropriate system calls such as
136. 5:09fork or spoon
137. 5:11okay
138. 5:12so the process which does the creating
139. 5:15is termed the parent
140. 5:17of the other process
141. 5:19so which is termed as its child
142. 5:23okay so each process is given an integer
143. 5:26identifier
144. 5:27okay we have here a process id
145. 5:30or the pid
146. 5:33okay
147. 5:34so
148. 5:35the parent pid is also stored on each of
149. 5:38the process
150. 5:40okay
151. 5:41so on a typical unix systems the process
152. 5:44scheduler is termed sched
153. 5:46and is given a pid of zero
154. 5:50all right so the first thing it does at
155. 5:54system startup time
156. 5:55is to launch init
157. 5:58or initialize
158. 6:00which gives the process pid equals one
159. 6:03okay
160. 6:04the init or initialize then launches all
161. 6:07system demons
162. 6:09and user logins and becomes the ultimate
163. 6:11parent for all the processes here
164. 6:15okay so depending on the system
165. 6:17implementation
166. 6:18a system process may receive some amount
167. 6:21of shared resources
168. 6:23with its parent
169. 6:25so the child processes may or may not
170. 6:29be limited to subsets
171. 6:31of the resources originally allocated to
172. 6:33a parent
173. 6:35so preventing runaway children
174. 6:37from consuming all of certain system
175. 6:41resources
176. 6:43all right
177. 6:46okay so i have here a c program for king
178. 6:50separate process so this is written in c
179. 6:53okay
180. 6:54so it shows a typical process tree for
181. 6:57linux system and other systems will have
182. 6:59similar
183. 7:00do not identical trees
184. 7:03okay referring to the previous diagram
185. 7:06okay
186. 7:07next would be creating a separate
187. 7:09process via the windows api okay so
188. 7:12mostly
189. 7:14the operating systems are made of or
190. 7:16made from the c or c c language c plus
191. 7:19plus
192. 7:20okay
193. 7:21so in here it shows more complicated
194. 7:24process for windows okay
195. 7:26so you'll have sort of um pointers
196. 7:30all right or memory by reference
197. 7:33which must provide all the parameter
198. 7:36information
199. 7:37for new process as part of the forking
200. 7:39process
201. 7:41okay
202. 7:42next would be process termination
203. 7:45so how do we terminate a process so we
204. 7:47just close the application
205. 7:50okay then we are terminating a process
206. 7:53so process may be terminated by the
207. 7:55system for a variety of reasons
208. 7:57including first
209. 7:59the inability of the system to deliver
210. 8:00necessary system resources
211. 8:05okay
212. 8:06in response to a kill command
213. 8:08or other unhandled process interrupt so
214. 8:11the parent may kill its children
215. 8:15if the task assigned to them is no
216. 8:17longer needed
217. 8:18so again we say kill here
218. 8:20okay so we mean termination we mean we
219. 8:24close the application
220. 8:26okay
221. 8:27so on unix systems or panned processes
222. 8:31are generally inherited by init
223. 8:35which then proceeds to kill them
224. 8:38the unix no hop command allows a child
225. 8:41to continue executing after the parent
226. 8:43has exited
227. 8:45okay
228. 8:46so
229. 8:49that is in the process termination
230. 8:51concepts in unix
231. 8:54all right
232. 8:56next when a process terminates
233. 8:58all of its system resources are freed up
234. 9:01open files flashed and closed okay so
235. 9:05the process termination status and
236. 9:07execution times
237. 9:08are returned to the parent if the parent
238. 9:10is waiting for the child to terminate or
239. 9:13eventually
240. 9:14return to init
241. 9:16if the process becomes an orpan
242. 9:20okay so we have here the term orphan
243. 9:24process which are trying to terminate
244. 9:26but which cannot because their parent
245. 9:29is not wanting for them
246. 9:31and termed zombies
247. 9:33okay so if no parent is waiting did not
248. 9:36invoke the weight the process is what we
249. 9:38call a zombie
250. 9:40if the parent is terminated without
251. 9:42invoking weight the process is called an
252. 9:44orphan
253. 9:45okay so these are eventually inherited
254. 9:48by init as orphans and killed off
255. 9:51so note that modern unique shells do not
256. 9:54produce as many our puns and zombies as
257. 9:57the older systems do
258. 10:00all right so we have that term zombie
259. 10:02and rpa
260. 10:05okay
261. 10:07so next would be the android process
262. 10:10importance hierarchy
263. 10:12okay
264. 10:13so mobile operating system often have
265. 10:16determinate process to reclaim the
266. 10:18system resources such as the memory
267. 10:21from most to least important so
268. 10:22foreground process visible process
269. 10:24service processes
270. 10:26background and empty processes
271. 10:28okay so android will begin terminating
272. 10:30the process that are least important
273. 10:33okay so take note that maybe you are
274. 10:35experiencing a fast
275. 10:37uh low bet on a mobile devices
276. 10:41and maybe without noticing it you have a
277. 10:43lot of processes running on your system
278. 10:46okay so we can store we we can save the
279. 10:49resource okay by closing the
280. 10:51applications
281. 10:52which you don't need
282. 10:54okay
283. 10:55so and with that
284. 10:57okay so we are freeing the resources
285. 11:00specifically the ram
286. 11:04all right
287. 11:06next let's talk about the multi-process
288. 11:09architecture so let's talk about the
289. 11:11chrome browser okay so many websites
290. 11:14active content such as javascript flash
291. 11:17html5 okay so to provide rich media
292. 11:21and dynamic web browsing experience
293. 11:25unfortunately
294. 11:26this web application may contain
295. 11:29software bugs
296. 11:31which result in sluggish response
297. 11:34and can never cause the browser to cross
298. 11:37okay
299. 11:39now
300. 11:40the google chrome browser
301. 11:42is a multi-process with three different
302. 11:45types of processes
303. 11:46okay you've got a browser
304. 11:49okay so process manages user interface
305. 11:52disk and network io
306. 11:54you also have the renderer okay so the
307. 11:57process
308. 11:58renders web pages
309. 12:00deals with html and javascript
310. 12:03a new renderer created for each website
311. 12:05opened
312. 12:07okay
313. 12:08runs in sandbox
314. 12:09restricting disk and io or specifically
315. 12:12the network io minimizing the effect of
316. 12:15the security exploits
317. 12:18all right
318. 12:20so the advantage of a multi-process
319. 12:22approach is that the website run in
320. 12:25isolation from one computer
321. 12:27so if the website crosses it only
322. 12:30okay affects or only its renderer
323. 12:33process is affected
324. 12:36okay
325. 12:36so all other processes remain unharmed
326. 12:39so furthermore
327. 12:40render our process which is mentioned
328. 12:43earlier running in a sandbox which means
329. 12:46that the access to disk and network io
330. 12:49is restricted
331. 12:50okay minimizing
332. 12:52the effects of any security exploits
333. 12:55here
334. 12:58okay
335. 12:59so each tab in a chrome represents a
336. 13:02separate process
337. 13:15[Music]
338. 13:23you