pipes 2 — Transcript

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1. 0:00Good morning. Let's start with the
2. 0:03second part of the introduction to pipe
3. 0:05programming. Now let's see the example
4. 0:11problem. Thank you very much. The
5. 0:13example problem is a pipe exercise that
6. 0:17involves creating a chat between
7. 0:19related processes. The objectives of
8. 0:23this exercise are to learn the basic
9. 0:25features of concurrent programming, the
10. 0:28mechanisms used by the operating system
11. 0:30to create processes, and the use of the
12. 0:33pipe resource for communication between
13. 0:35related processes. The exercise
14. 0:38approach consists of creating a
15. 0:40structure of related processes with
16. 0:43five processes. A parent process will
17. 0:46create two child processes, and each
18. 0:48child process will create a grandchild
19. 0:50process. Process creation is done using
20. 0:53the for system call. The chat will be
21. 0:56carried out between the child processes
22. 0:58, which will be the writers, and each
23. 1:00grandchild process will be the reader
24. 1:02of its corresponding writer. It was
25. 1:05decided to use two pipes as a
26. 1:06communication resource between
27. 1:08processes in order to make programming
28. 1:10simpler and focus the problem on the
29. 1:13concept. It is recommended that the
30. 1:15student complete the same exercise
31. 1:17using a single pipe. Here is the
32. 1:20diagram of the approach. We see a
33. 1:22parent process that creates a child one
34. 1:25and a child two with two for. Then
35. 1:29child one creates grandchild one with a
36. 1:31fork. Child two creates grandchild two
37. 1:33with a fork. Then we see the pipes that
38. 1:37are going to be used for interprocess
39. 1:39communication in the chat. Child one is
40. 1:43going to write to pipe 2, child two is
41. 1:46going to write to pipe 1. Grandchild
42. 1:48one is going to read to child one from
43. 1:51pipe 1. And grandchild two is going to
44. 1:54read from pipe 2 to child two. Child
45. 1:58two, uh, sorry, child one and child two
46. 2:00are going to receive keyboard input,
47. 2:03which is what users are going to type
48. 2:05for the chat, and the grandchildren are
49. 2:08going to display on the screen what
50. 2:10they read from the pipes. Okay, let's
51. 2:13see the description of the approach.
52. 2:15What should the parent do? The parent
53. 2:18should create the two pipe resources,
54. 2:20pipe 1 and pipe 2. It begins the
55. 2:23creation of the process structure. It
56. 2:26specifies that it will not be a writer
57. 2:29or reader of any of the pipes and waits
58. 2:31for child one and child two to finish.
59. 2:34And then it finishes. creates the pipes
60. 2:40with the pipe call passing it the
61. 2:43vectors pipe 1 and p 2 as arguments.
62. 2:48Okay, now we see the creation of the
63. 2:50process structure. The red arrow marks
64. 2:54the fork that will create child one.
65. 2:58The green arrow marks the fork where
66. 3:00child two will be created. What is
67. 3:03highlighted in yellow is the most
68. 3:05important part of the parent, which is
69. 3:08closing all the descriptors of the read
70. 3:11and write pipes. The blue part is where
71. 3:14child two creates grandchild two and
72. 3:17the pink part is where child one
73. 3:20creates grandchild one. Another part to
74. 3:23highlight about the parent process is
75. 3:26that it has to wait for the termination
76. 3:28of child one and child two and then it
77. 3:31ends. There we have the code that does
78. 3:34what we are proposing. I choose one. It
79. 3:38will only be a writer of pipe 2. The
80. 3:40message it writes to pipe 2 is obtained
81. 3:43from standard input. Reading from
82. 3:47standard input ends when it gets stream
83. 3:51chau and waits for grandchild 1 to
84. 3:54finish. Child 2 will only be a writer
85. 3:58to pipe 1. The message it writes to
86. 4:00pipe 1 is obtained from standard input.
87. 4:04Reading from standard input ends when
88. 4:07it gets stream chu and waits for
89. 4:09grandchild 2 to finish. Grandchild 1
90. 4:13will only be a reader of pipe 1.
91. 4:15Reading from the pipe writes to
92. 4:17standard output and ends when it reads
93. 4:20stream ch from the pipe. Grandchild 2
94. 4:24will only be a reader of pipe 2.
95. 4:26Reading from the pipe writes to
96. 4:28standard output and ends when it reads
97. 4:30stream ch from the pipe. Well, we are
98. 4:34going to implement this example in an
99. 4:38operational environment, in a Linus
100. 4:41Deviant operating environment using the
101. 4:44C language. Well, this concludes the
102. 4:47second part of the introduction to Pipe
103. 4:49programming. Thank you very much and we
104. 4:52look forward to the third part. M.