Sistemas Operativos, Procesos 8 Comunicación entre procesos — Transcript

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1. 0:00Hello, how are you? How are you doing?
2. 0:03Welcome back to the Operating Systems
3. 0:05Fundamentals course. We are looking at
4. 0:09the processes topic from chapter 3 of
5. 0:11the Silberschatz and Galvin textbook.
6. 0:15What we are going to look at next is
7. 0:18inter-process communication and we will
8. 0:20also talk a bit about synchronization,
9. 0:23meaning we will cover inter-process
10. 0:25communication and what those initials,
11. 0:28IPC, stand for. Well, they stand for
12. 0:31inter-process communication. The first
13. 0:37mechanism we will discuss is called
14. 0:39signals. What are signals? Signals are
15. 0:44notifications that one process can send
16. 0:47to another, so that when the process
17. 0:50receives a signal, it will react in
18. 0:53some way. In this way, the operating
19. 0:57system ensures that the process
20. 0:59receiving the signal handles it
21. 1:02immediately. Here we have, for example,
22. 1:05two processes, process one and process
23. 1:06two. The moment process one sends a
24. 1:10signal to process two, process two will
25. 1:13react to that signal, okay? It will
26. 1:16take action to handle that signal. Okay
27. 1:21? Another mechanism we are going to see
28. 1:26, and which we will cover starting from
29. 1:29, in fact, one of the labs (we could
30. 1:31use it starting from lab two), but
31. 1:33especially, for example, in the second
32. 1:36midterm, which is where we will see all
33. 1:39these communication and synchronization
34. 1:41mechanisms in more depth and detail.
35. 1:45One of them is shared memory. What is
36. 1:48shared memory? It is a shared resource
37. 1:50provided by Unix. Available to programs
38. 1:54so they can exchange information.
39. 1:57Agreed? In this way, for example, I can
40. 2:01have one process reading and writing to
41. 2:04a memory area where another process can
42. 2:07also be performing read and write
43. 2:09operations, and with shared memory, the
44. 2:12processes could exchange information.
45. 2:18Another mechanism, perhaps one of the
46. 2:20most important ones we will see in the
47. 2:23second midterm, is semaphores. What are
48. 2:26semaphores? It is a mechanism provided
49. 2:29by the operating system, in this case
50. 2:31Unix, available to programs so they can
51. 2:34synchronize. What does it mean to
52. 2:37synchronize? Well, let's look, for
53. 2:40example, at the case where I have two
54. 2:43processes and only one can pass through
55. 2:46here. Why? Because there is no space
56. 2:49for both processes to pass. What will
57. 2:52happen? Well, as long as the semaphore
58. 2:54is green, one of the two can pass.
59. 2:56Agreed? What will happen? When one
60. 2:59starts to pass, the semaphore changes
61. 3:01to red. When it finishes passing, the
62. 3:04semaphore turns green, giving way to
63. 3:06another process. And when that one
64. 3:09finishes, well, the semaphore returns
65. 3:10to green. Okay. Another mechanism we
66. 3:17are going to see is the message system.
67. 3:20What is the message system? Well, it is
68. 3:23a message system, a mechanism provided
69. 3:25by the Unix operating system. made
70. 3:29available to programs so they can
71. 3:31exchange information and synchronize.
72. 3:35In this way, for example, we can place
73. 3:38a message mailbox between processes and
74. 3:41the processes can send messages to that
75. 3:44mailbox and can receive messages from
76. 3:46that mailbox. These are one of the few
77. 3:51inter-process communication mechanisms
78. 3:53and later we will address some of them
79. 3:55in more detail. Thank you very much for
80. 3:59your attention and I am available to
81. 4:02answer any questions.