04 01 Threads and Concurrency Part 1a — Transcript

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1. 0:01[Music]
2. 0:08[Music]
3. 0:20hello there
4. 0:22this video lecture covers
5. 0:25threads
6. 0:26and concurrency
7. 0:28okay so this topic is next to processes
8. 0:32okay so the last video that we had
9. 0:35all right
10. 0:36so let's get started
11. 0:38so bear with me this discussion is a
12. 0:40little bit too technical okay and we
13. 0:43will be dealing with a lot of terms here
14. 0:46okay so for the outline of the video so
15. 0:50we will be dealing with an overview
16. 0:52of a thread okay
17. 0:55so also included are the multi-core
18. 0:58programming
19. 0:59the multi-threading models the thread
20. 1:02libraries
21. 1:03implicit threading
22. 1:05the threading issues and some operating
23. 1:08system examples when it comes to threads
24. 1:12okay so at the end of this discussion so
25. 1:16we should be able to identify the basic
26. 1:17components of a thread
27. 1:20and contrast threads and processes so
28. 1:24last time we we talked about process and
29. 1:27when she processed this is a programming
30. 1:29execution okay so how about threads so
31. 1:32threads
32. 1:33before okay
33. 1:35during the process discussion we defined
34. 1:37it as
35. 1:38a sub process
36. 1:40all right
37. 1:42next would be
38. 1:43describe the benefits and challenges of
39. 1:46designing a multi-threaded applications
40. 1:49illustrate different approaches to
41. 1:52implicit trading including tread pools
42. 1:55fork join
43. 1:56and grand central dispatch
44. 2:00so describe how windows and linux
45. 2:02operating systems
46. 2:04represent threads
47. 2:05and design a multi-threaded application
48. 2:08using the pthreads java and the windows
49. 2:12trading apis
50. 2:24[Music]
51. 2:32so let's start with the definition of
52. 2:35thread so what is the thread okay
53. 2:37so thread basically is a basic unit of
54. 2:40cpu utilization
55. 2:42consisting of a program counter
56. 2:45a stack
57. 2:46and a set of registers
58. 2:49and a thread id
59. 2:51okay
60. 2:52so what what are the motivations for
61. 2:54having a thread
62. 2:56okay so most modern applications are
63. 2:59multi-threaded
64. 3:01okay so threads run within application
65. 3:05so that means
66. 3:07thread is
67. 3:09a sub process
68. 3:11okay so multiple tasks
69. 3:13with the application can be implemented
70. 3:15by separate threads so update display
71. 3:20fetch data spell checking so our example
72. 3:23is of course in microsoft word okay so
73. 3:26we're in when we run the application we
74. 3:28have a lot of threads okay so that was
75. 3:31initialized when we open it
76. 3:34okay and then answer a network request
77. 3:37is also
78. 3:38a good example
79. 3:40okay so process creation is a heavy
80. 3:44weight
81. 3:45while trend creation is a light rate so
82. 3:47that's why we have the motivation for
83. 3:50creating a thread okay so it can simply
84. 3:53simplify the code and increase
85. 3:55efficiency
86. 3:57kernels are generally multi-threaded
87. 4:00okay
88. 4:01so basically threads are very useful in
89. 4:04modern programming
90. 4:05so whenever a process has multiple tasks
91. 4:08to perform independently
92. 4:10of the others
93. 4:11okay so a good uh multi-threaded
94. 4:15application for programming is of course
95. 4:17java
96. 4:18okay
97. 4:19so this is particularly true when one of
98. 4:22the tasks may block
99. 4:25and it is desired to allow the other
100. 4:27tasks to proceed without blocking so for
101. 4:30example
102. 4:32so in a word processor
103. 4:34a background thread may check spelling
104. 4:36and grammar
105. 4:38while a foreground thread
106. 4:40process or processes user inputs like
107. 4:42keystrokes
108. 4:44okay
109. 4:45so while yet a third thread loads images
110. 4:49from the hard drive and the fourth does
111. 4:51periodic automatic backups
112. 4:54of the file being edited okay
113. 4:56so let me open here
114. 5:00a
115. 5:01[Music]
116. 5:03task manager so that we'll be able to
117. 5:05see the threads there okay
118. 5:19all right
119. 5:20so we have here our task manager okay so
120. 5:24of course we have here the process is
121. 5:26running
122. 5:27okay
123. 5:28and basically you'll have the background
124. 5:30processes and
125. 5:32some foreground processes running here
126. 5:34okay or the windows processes
127. 5:37now so these are the resources allocated
128. 5:40to each of the process
129. 5:41okay
130. 5:42now looking at the performance so let's
131. 5:45examine the cpu utilization here so the
132. 5:48cpu utilization is 36 percent so i'm
133. 5:51using 2.7
134. 5:54okay plus plus gigahertz
135. 5:56of the cpu frequency here
136. 5:59okay
137. 6:00now
138. 6:01if you will observe here with a 38
139. 6:04utilization okay and the speed of 2.74
140. 6:07though the cpu is basically 2.3
141. 6:09gigahertz so you'll you'll have that um
142. 6:12it exceeded the the frequency okay now
143. 6:15what i want you to pay attention here is
144. 6:18the number of processes here okay
145. 6:21now for the number of processes so
146. 6:23currently we are running 155 processes
147. 6:27and there are about
148. 6:291683 threads
149. 6:31okay so if you are running virtual
150. 6:33machines like virtualbox so you would
151. 6:35also see here if you have enabled the
152. 6:38virtualization on the
153. 6:41cmos
154. 6:42all right
155. 6:43now
156. 6:44so currently i'm running 153 processors
157. 6:47and with that processes there are about
158. 6:49a thousand six hundred plus threads okay
159. 6:53so let me open ms word here okay
160. 6:57so windward
161. 7:01let me open it and what i want you to
162. 7:03pay attention with is the number of
163. 7:05threads there okay
164. 7:06so
165. 7:08examine or observe what will happen
166. 7:10when i open ms word
167. 7:15all right so there is a sudden increase
168. 7:18of the number of threads
169. 7:20okay
170. 7:21so we just opened microsoft word there
171. 7:23all right
172. 7:24and microsoft word has a lot of threads
173. 7:26associated with it so as mentioned
174. 7:28earlier so this includes like spelling
175. 7:31check
176. 7:32okay
177. 7:33uh grammar check
178. 7:35what else uh the keystrokes the number
179. 7:37of characters and so on
180. 7:39okay
181. 7:41so let me close this
182. 7:44all right so
183. 7:46next
184. 7:52okay so we have
185. 7:54what we call a single threaded or a
186. 7:56multi-threaded processes
187. 7:59so traditionally
188. 8:01we've got the heavyweight processes
189. 8:03it has a single thread of control so
190. 8:06there is one program counter
191. 8:08and a sequence or one sequence of
192. 8:10instructions that can carry it out at
193. 8:13any given time
194. 8:15okay now as shown in this diagram here
195. 8:18okay so we've got a multi-threaded
196. 8:21applications
197. 8:22okay and it has multiple threads with a
198. 8:25single process
199. 8:27okay
200. 8:28so you've got multiple threads here okay
201. 8:30so this string
202. 8:32like
203. 8:34diagram or symbol here represents a
204. 8:36thread okay
205. 8:38now we have here
206. 8:40a multi-threaded process if you will
207. 8:42observe we have three
208. 8:43threads running with a single process
209. 8:46and each of the thread has their own
210. 8:48registers stack and program counter
211. 8:51but the code the data and the files are
212. 8:54shared among the threads
213. 8:57all right
214. 9:03all right
215. 9:04so next would be the multi-threaded
216. 9:06server architecture okay so what do we
217. 9:09have in the multi-threaded architecture
218. 9:12so another example of
219. 9:14a thread okay so like what we've
220. 9:16mentioned earlier ms word example so
221. 9:19another example is the web server
222. 9:21so multiple threads allows or allow for
223. 9:24multiple requests to be satisfied
224. 9:26simultaneously okay without having to
225. 9:29service the request sequentially
226. 9:31or to fork
227. 9:33separate processes for every incoming
228. 9:35request
229. 9:36okay
230. 9:37so a dame one would listen at a port
231. 9:41fork of a child for every incoming
232. 9:43request
233. 9:44to process
234. 9:46and then
235. 9:47go back to the listening port
236. 9:50all right
237. 9:51so
238. 9:52that is shown on this diagram here
239. 9:56okay
240. 9:57so next would be
241. 10:00what are the benefits of a trend
242. 10:03okay so basically there are four major
243. 10:05categories of benefits
244. 10:07to multi-threading so these are
245. 10:09responsiveness
246. 10:10resource sharing economy and scalability
247. 10:14okay
248. 10:15now on the responsiveness so one thread
249. 10:18may provide rapid response while other
250. 10:21threads are blocked or slowed down doing
251. 10:24intensive calculations
252. 10:27all right
253. 10:28so next would be resource sharing
254. 10:31so by default
255. 10:32threads share common code data and other
256. 10:35resources as shown in the model earlier
257. 10:37okay so which allows multiple tasks
258. 10:41to be performed simultaneously in a
259. 10:43single address space
260. 10:45that's resource sharing
261. 10:47okay
262. 10:49third is economy
263. 10:51so creating and managing threads and
264. 10:53contact switches between them
265. 10:55is much faster than performing
266. 10:58same tasks for processes
267. 11:01all right so that's economy
268. 11:03and the last one would be scalability so
269. 11:05an example of this is the utilization of
270. 11:08a multi-processor architectures
271. 11:10okay so a single threaded process can
272. 11:12only run one or can only run on one cpu
273. 11:16no matter how many
274. 11:18may be available
275. 11:20whereas the execution of a
276. 11:21multi-threaded application
277. 11:23may be split amongst available
278. 11:25processors
279. 11:27okay so note that a single threaded
280. 11:29process can still benefit from a
281. 11:31multi-processor architectures
282. 11:34when there are multiple processes
283. 11:36contending for the cpu
284. 11:38example when the load average is above
285. 11:41some certain threshold
286. 11:43okay so
287. 11:45basically the use of threads are
288. 11:47beneficial
289. 11:49all right
290. 11:54[Music]
291. 12:06you