03 06 Processes Part 6 — Transcript

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1. 0:08[Music]
2. 0:20okay so next are pipes
3. 0:23so what are pipes
4. 0:24pipes are one of the earliest and
5. 0:26simplest channel of communication
6. 0:28between unix processes
7. 0:31okay
8. 0:32so there are four key considerations for
9. 0:34implementing pipes
10. 0:37first
11. 0:38unidirectional or bi-directional
12. 0:40communication
13. 0:41right
14. 0:43next is
15. 0:45is bi-directional operation or
16. 0:47communication half duplex or full duplex
17. 0:50okay
18. 0:52now next would be
19. 0:54must a relationship such as parent child
20. 0:56exist between the processes
21. 1:00okay and last
22. 1:02is can pipes communicate over a network
23. 1:05or only on the same machine
24. 1:07so the following sections examine these
25. 1:09issues on unix and windows
26. 1:12so you've got what's called an ordinary
27. 1:14pipes and the name pipes
28. 1:17okay
29. 1:17now let's talk about the ordinary pipes
30. 1:19here
31. 1:21ordinary pipes are unidirectional
32. 1:24with a reading and and writing in
33. 1:27so if bi-directional
34. 1:30meaning two-way
35. 1:31okay communications are needed then a
36. 1:34second pipe is required
37. 1:38okay
38. 1:40so unix pipes are accessible as files
39. 1:43using the standard read and write system
40. 1:46calls
41. 1:47so the ordinary pipes are only
42. 1:49accessible within the process that
43. 1:51created them so typically a prior
44. 1:54apparent okay creates the pipe before
45. 1:57forking off a child
46. 1:59so when the child inherits open files
47. 2:02from each parent
48. 2:03including the pipe files
49. 2:06a channel of communication is
50. 2:08established
51. 2:09so each process
52. 2:11parent and child should first close the
53. 2:13ends of the pipe
54. 2:15that they are not using so for example
55. 2:18if the parent is waiting
56. 2:20to the pipe and the child is reading
57. 2:23then the parent should close the reading
58. 2:25end
59. 2:26of its pipe after the fork and the child
60. 2:29should close the
61. 2:31writing end
62. 2:33so in windows
63. 2:35windows calls this anonymous pipes so
64. 2:38ordinary pipes and unix anonymous pipes
65. 2:41and windows
66. 2:43okay
67. 2:44next how about the name pipes
68. 2:48so name pipes support bi-directional
69. 2:51communication so communication between
70. 2:53a non-parent child related process
71. 2:56and persistence after the process
72. 2:59which created them exist
73. 3:01so multiple processes can also share a
74. 3:04named pipe
75. 3:05typically
76. 3:06one reader and multiple writers
77. 3:10okay so in unix
78. 3:12named pipes are termed
79. 3:14pifos
80. 3:16okay appear as ordinary files in the
81. 3:19system so in windows
82. 3:22named pipes provide richer
83. 3:23communications duplex
84. 3:26specifically full duplex is supported
85. 3:29so process may reside on the same or
86. 3:31different machines
87. 3:33and created and manipulated using the
88. 3:37create name type
89. 3:39connect name type read file and write
90. 3:42file
91. 3:43system calls
92. 3:46okay
93. 3:49all right so a lot of technical terms
94. 3:52and technical discussions okay
95. 3:54all about processes
96. 3:56okay and
97. 3:58a lot more technical discussions on the
98. 4:00next chapter
99. 4:02okay
100. 4:03now communications in the client server
101. 4:05systems
102. 4:06so how do we communicate computers with
103. 4:09ourselves to be the client
104. 4:12to the server which is the provider of
105. 4:13service
106. 4:14okay so we have two it's added we use
107. 4:17sockets
108. 4:18or the remote procedure calls sockets
109. 4:21earlier
110. 4:22is termed as port
111. 4:24or
112. 4:25mailboxes okay
113. 4:27now what is a socket
114. 4:30so a socket is defined as an endpoint
115. 4:32for communication
116. 4:34a socket is an end point for
117. 4:37communication so that means
118. 4:39every applications that is capable of
119. 4:41having a communication
120. 4:43over the network has a socket
121. 4:46example
122. 4:47when you use or when you browse the
123. 4:49internet you are using http
124. 4:51so you are using a port 80 socket
125. 4:55or if it is an https you are using a
126. 4:58port 443 seconds
127. 5:01okay
128. 5:02so two process communications are
129. 5:04communicating over the network often use
130. 5:06a pair of connected sockets as mentioned
131. 5:08earlier
132. 5:09so software that is designed for a
133. 5:11client server operation may also use
134. 5:14sockets for communication between two
135. 5:16processes
136. 5:17running on the same computer for example
137. 5:20the ui for a database program may
138. 5:22communicate with a backend database
139. 5:24manager using sockets
140. 5:26again when you see sockets just to make
141. 5:28it clear
142. 5:29sockets are port numbers
143. 5:32these are the address of the
144. 5:34applications
145. 5:35residing on your
146. 5:36computer okay so if your computer has a
147. 5:39physical address called mac address
148. 5:42and the logical address called ip
149. 5:45address
150. 5:46your computer's application or the
151. 5:48application inside your computer
152. 5:50has watched called address named socket
153. 5:53or port
154. 5:55okay
155. 5:59next
156. 6:01so this is an example of a socket
157. 6:02communication okay so if you'll observe
158. 6:05here we have here a socket 1625 in a
159. 6:08socket
160. 6:09um
161. 6:1180
162. 6:12right so you've got the communication
163. 6:14between the host
164. 6:16at 146 86 520
165. 6:19communicating to the server at 161 25
166. 6:221988
167. 6:24okay
168. 6:25so take note that
169. 6:26with socket communication okay
170. 6:29so
171. 6:30it is not only the ip address which is
172. 6:32being used in the process but it
173. 6:34includes or integrates the part number
174. 6:37or socket numbers
175. 6:38okay
176. 6:39so
177. 6:40in cisco
178. 6:42we are dealing with a lot of port
179. 6:44numbers
180. 6:45especially when we're talking about the
181. 6:47access lists
182. 6:48okay
183. 6:49so the communication channels via
184. 6:51sockets may be one or
185. 6:54uh two of the major forms okay it's
186. 6:57either tcp connection oriented
187. 7:00transmission control protocol
188. 7:02and udp
189. 7:04so i guess you you remember
190. 7:06already what are these sockets for
191. 7:10okay
192. 7:12now
193. 7:13sockets in java
194. 7:15so there are three types of sockets as
195. 7:18mentioned earlier you've got the
196. 7:20connection oriented tcp
197. 7:22it is a reliable communication okay so
198. 7:25there it's
199. 7:26called reliable because
200. 7:27this requires
201. 7:29an acknowledgement
202. 7:30okay
203. 7:31connectionless are udp this is said to
204. 7:34be non-reliable
205. 7:36but java has this multicast socket
206. 7:40okay so data can be sent to multiple
207. 7:43recipients
208. 7:46okay
209. 7:46so sockets are considered a low-level
210. 7:48communication channel
211. 7:50and process may often choose to use
212. 7:52something at a higher level such as
213. 7:55those covered in
214. 7:56the next two sections
215. 7:58okay
216. 8:00now the figure
217. 8:03client server systems illustrated here
218. 8:07okay so for determining the current date
219. 8:09using
220. 8:10sockets in java
221. 8:13okay
222. 8:16now
223. 8:18next would be
224. 8:19the remote procedure calls or rpcs
225. 8:22okay
226. 8:23so remote procedure call abstracts
227. 8:25procedure calls between process or
228. 8:28processes of network systems again
229. 8:31uses ports for service differentiation
230. 8:34again so don't be confused with the
231. 8:36ports sockets mailbox they are all the
232. 8:39same
233. 8:40okay
234. 8:41next the general concept of rpc is to
235. 8:44make procedure calls similarly to
236. 8:46calling on ordinary local procedures in
237. 8:49programming
238. 8:50except the procedure being called
239. 8:53lies on remote machines
240. 8:55so implementation involves what you call
241. 8:58stubs
242. 8:59okay
243. 9:00on either end of the communication so
244. 9:02the local process calls on the stab
245. 9:04much as it would call upon
246. 9:07a local procedure
247. 9:08so the rpc system package up marshalls
248. 9:12okay the parameters of the procedure
249. 9:14call and transmits them to the remote
250. 9:17system
251. 9:19on the other remote
252. 9:20side the rpc daemon accepts the
253. 9:23parameters and calls upon the
254. 9:24appropriate
255. 9:25a remote procedure
256. 9:27to perform
257. 9:29the requested work
258. 9:31so any results
259. 9:33should be returned from the package up
260. 9:36and sent back to the rpc systems to the
261. 9:39local system
262. 9:41so which then unpackages
263. 9:44and returns the result to the local
264. 9:46calling procedures
265. 9:49so on windows
266. 9:51this tab code compiled from
267. 9:53specification written in the microsoft
268. 9:55interface definition language
269. 9:57rmitl
270. 10:00okay
271. 10:01next
272. 10:04so
273. 10:05one potential difficulty
274. 10:08is the formatting of data on local
275. 10:10versus remote systems
276. 10:12okay
277. 10:13so the resolution of this problem
278. 10:15generally involves an agreed-upon
279. 10:17intermediary format such as the xdr
280. 10:20okay or the external data representation
281. 10:24all right so another issue is
282. 10:26identifying the procedure on the remote
283. 10:28system particularly the rpc is destined
284. 10:32for
285. 10:33so remote procedure calls
286. 10:35are identified by ports
287. 10:38though not the same ports as the sockets
288. 10:41port described earlier
289. 10:44okay so one solution is for the calling
290. 10:47procedures to know the port number they
291. 10:49wish to communicate with
292. 10:52on the remote system so this is
293. 10:54problematic as the port number would be
294. 10:56compiled into code
295. 10:58and it makes breakdown if the remote
296. 11:00systems cannot
297. 11:02change their port numbers
298. 11:05okay so more commonly matchmakers
299. 11:08process is employed
300. 11:10which acts like a telephone directory
301. 11:12service
302. 11:14okay so the local process must first
303. 11:16contact the matchmaker
304. 11:19of the remote system
305. 11:21so at a well-known port numbers
306. 11:24okay so which looks up
307. 11:27the desired port number and return set
308. 11:29so the local process can then choose and
309. 11:32use that information
310. 11:34to contact direct remote procedure
311. 11:38so this operation involves
312. 11:40an extra step but
313. 11:43it's more flexible
314. 11:45okay so an example of the matchmaker
315. 11:48process
316. 11:49is illustrated here
317. 11:53okay so this is how
318. 11:55the client
319. 11:57and the server
320. 11:58communicate with each other
321. 12:00by using the remote procedure calls
322. 12:04so one common example of the system
323. 12:06based on rpc calls is the network file
324. 12:08system
325. 12:10okay messages are passed to read
326. 12:14write delete
327. 12:16rename or check status
328. 12:19or might be for ordinary local disk
329. 12:22access requests
330. 12:24okay
331. 12:25so
332. 12:26we have a long day with a discussion of
333. 12:29this chapter because we have a lot of
334. 12:31technical discussions and technical
335. 12:33terms here
336. 12:34okay thanks so much for the next chapter
337. 12:38so
338. 12:39that's the end of the video
339. 12:41thank you for sticking around
340. 12:44have a great day
341. 12:54[Music]
342. 13:02you