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03 01 Processes Part 1 — Transcript

by Santelmo · 2,331 words · 480 segments · language en · Watch on YouTube

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0:08[Music]
0:20hi good day
0:23on this video lecture
0:24so we are going to cover discussions on
0:29operating system processes
0:33so here's the outline of the
0:36presentation so we are going to deal
0:38with the following
0:40so you've got a process concept
0:43process scheduling
0:45operations on processes
0:48the inter-process communication
0:51ipc or the inter-process communication
0:53and shared memory systems
0:56the inter-process communication in
0:58message passing systems
1:01so we also deal with examples of the
1:03inter-process communication systems
1:06and the communication in the client
1:08server systems
1:13all right
1:14so the objective of our video or
1:17objectives of the video so would be the
1:19following so first
1:21identify the separate components of a
1:24process and illustrate how they are
1:26represented and scheduled in an
1:28operating system
1:30okay so second is describe how
1:32processors are created and terminated in
1:34an operating system so including
1:37developing programs using the
1:39appropriate system calls
1:41that perform these operations
1:44okay so third is to describe
1:48and contrast the inter-process
1:50communication using
1:52shared memory and message passing
1:56forties design programs that uses pipes
1:59and posix shared memory to perform the
2:02inter-process communication or ipc
2:06so to describe the client server
2:07communication using sockets and remote
2:10procedure calls
2:11right and last would be to design kernel
2:14modules that interact with the linux
2:16operating systems
2:19so let's start
2:21so let's start with the definition of a
2:23process so what is a process
2:26in an operating systems
2:29okay so basically when you say process
2:31we're talking about the instance of
2:32program execution
2:35okay a process is basically
2:37a program in
2:39execution
2:40so process execution must progress in
2:43sequential fashion
2:45no parallel execution of instructions of
2:48a single process
2:49so basically in layman's term when say
2:52process
2:54we run the program it creates a process
2:57the program itself that is not running
2:59is not considered to be a process so you
3:02run the applications and that would
3:04become a process
3:06okay
3:07so batch systems works in terms of jobs
3:10so on this discussion
3:13the process or the term process and jobs
3:15are used interchangeably
3:17so process is also the same as jobs and
3:20we talk about a program in
3:22execution
3:24okay
3:25so many many modern process concepts are
3:28still expressed in terms of jobs
3:30that's why some books you'll be hearing
3:32job scheduling
3:34okay
3:35or that is also the same with process
3:37scheduling or we call it cpu scheduling
3:40okay so these terms are used
3:42interchangeably throughout the
3:44discussion here okay
3:46so a process basically composed of
3:49multiple parts
3:51okay so you've got the program code
3:54also called the text section
3:57so currently our current activity
3:59including the program counter processor
4:02registers okay
4:03so stack containing the temporal data
4:06so function parameters return addresses
4:09and local variables
4:11so you also have data section containing
4:14the global variables and the heap
4:16containing memory dynamically allocated
4:19during runtime
4:25okay so a program is either passive or
4:29active okay so program is passive entity
4:33stored on the disk
4:34this or the executable file
4:37okay and when you say process we're
4:40talking about the active
4:42okay active program or running program
4:45so that is what we call a process okay
4:48so program becomes a process
4:51only when an executable file is loaded
4:53into the memory
4:54and being executed by the cpu
4:57okay so execution of programs started
5:00via gui okay so via mouse click so take
5:04note that when you click on the
5:05application you are actually starting a
5:07process
5:08okay or in the command line you simply
5:11type in the command okay so just make
5:13sure it is executable and that creates a
5:15process
5:17right so one program can have
5:20several processes
5:22consider multiple users executing the
5:24same program
5:26okay
5:28next
5:29so this diagram here represents a
5:32process in a memory
5:34okay so basically as mentioned earlier a
5:37process has the following so it has a
5:39stack
5:40heap
5:41data and text
5:44okay so process memory is divided into
5:47this four section as you can see here
5:50you've got to stop the heap the data and
5:52the text
5:53so let's start with a text section
5:56okay so the text section comprises the
5:58compiled program code
6:00read in from a non-volatile storage when
6:03the program is launched
6:06okay
6:07so the next one is data section it
6:09stores global and static variables
6:11allocated and initialized prior to
6:13executing the main
6:15function in a program
6:16okay so that's why
6:18for example in c plus we'll have the
6:20main function
6:22okay
6:24next is the hip
6:26okay
6:27so what is a hip hip is used for dynamic
6:29memory allocation
6:31and is managed by a calls to new delete
6:35the malloc or the memory allocation
6:39free and i recommend etc
6:42okay
6:43so the next one is stack so stack is
6:45used for local variables so space on the
6:48stock is reserved for local variables
6:51when they are declared okay at the
6:54function entrance
6:55or maybe elsewhere depending on the
6:57language
6:58all right and the space is freed up when
7:01the variables go out of the scope
7:04okay so note that the stock is also used
7:07for function return values
7:09and the exact mechanism of stock
7:11management
7:12may be language specific
7:14so maybe you are
7:16you you still remember
7:18okay so programming
7:20all right
7:21so we have declaration of the local and
7:24global variables in there so that works
7:26on
7:27the sub
7:29okay so note that the stock and the heap
7:32start at opposite ends of the process
7:34free space
7:35and grow towards each other so you'll
7:37have the space here
7:39okay
7:42and if they should ever meet
7:44then either the stock overflow error
7:46will occur
7:48okay else a call to a new or memory
7:51allocation or malloc
7:52will fail due to insufficient memory
7:55available
7:56okay so when a process are swapped out
8:00of the memory and later is stored
8:02additional information must also be
8:04stored
8:06and restored
8:07so key among them are the program
8:10counter
8:11and the value of all the program
8:12registers
8:14all right
8:16next so i have here an example of a
8:19memory layout of a c program
8:21so this is what uh what has been
8:23explained
8:24on the previous slides or in
8:26every time you declare variables so
8:29every time we
8:31we declare an identifier so they are
8:33mapped into the memory
8:36okay so the lower portion of memory is
8:38the text so what you call the text and
8:41these variables here
8:43are occupying the other portions of the
8:46memory
8:48all right
8:49now so
8:51when you say process as i said earlier
8:54this is a program and execution
8:56okay so if we are talking about the
9:01processes of this computer let me show
9:03you that okay so let me open
9:05a task manager here okay
9:08so
9:10this task manager here okay shows the
9:13number of processors running so
9:15basically they are represented by
9:18apps okay
9:19you've got the user processors here and
9:22i also have
9:23here some background processes
9:26all right
9:27now in here you will observe the
9:30allocation of the resources
9:32all right
9:33so for the allocation of the resources
9:35so basically your operating system
9:37allocates
9:39the cpu
9:41currently i'm using 20 of it the memory
9:44disk network and others
9:47now what i want you to pay attention
9:49with is the performance here
9:52and take a look at the number of
9:53processes
9:55which are being run by this computer
9:58okay so let me expand this
10:01so we've got processes here okay and
10:04then performance
10:07all right
10:08so
10:10these are the resources available on the
10:12cpu when you click on the cpu you'll
10:15have the processes there
10:17right
10:18so currently this computer is running
10:21170 processes but
10:23if you will observe you will only see
10:25some of the processes here
10:27because majority of the processes being
10:30run by your computer is part of the
10:31system or part of the operating system
10:34all right
10:35so
10:36again we have processes here that means
10:38this computer is running
10:41170 program at the current state
10:45okay and there are about 2
10:48370 plus plus
10:50threads
10:52okay
10:53now let's talk about the process state
10:56okay so each process each application we
10:58open and run passes through this
11:02state
11:02okay so basically we're going to start
11:05with new
11:06new is when the process is created
11:10running
11:11instructions are being executed
11:14waiting the process is waiting for some
11:16event to occur
11:18you've got already
11:21the process is waiting to be assigned to
11:23a processor and terminated the process
11:25has finished the execution
11:27okay so representing in terms of a
11:29diagram here so this represents the
11:31process state so initially when you open
11:34the application we are actually creating
11:37a new process
11:39okay
11:40the process is in the stage
11:43of being created so that's what we meant
11:45by news
11:47okay
11:48and then once admitted onto the memory
11:51so it will now be in red state
11:54so ready means the process has all the
11:56resources available that it needs
11:58to run but the cpu is not currently
12:01working on its process instructions
12:03so basically before we run an
12:05application before it is considered to
12:08be a process
12:09this application needs resources or this
12:12process needs resources
12:15okay
12:15and once it has the resources so it is
12:18now in ready state
12:20okay
12:21next state is running
12:23so after the ready state so you've got
12:25the running state there the cpu is
12:27working on its
12:29process instructions now
12:32and then waiting here
12:35waiting is caused by an io or an event
12:37rate
12:38okay
12:40or an i o completion so and then that
12:43would go to ready and then running again
12:46now waiting is the process cannot run at
12:49the moment
12:50because it is waiting for some resource
12:52to become available
12:54or for some events occur so for example
12:57the process
12:59may be waiting for a keyboard input
13:01or disk access request or enter process
13:05messages okay a timer go off
13:08or
13:09a child process to finish
13:11so that is waiting state
13:14all right
13:15so next would be
13:17terminated so the process has completed
13:20its operation
13:23all right
13:24next
13:26now let's talk about the process control
13:28block
13:29okay so what is a process control block
13:32so it has the information associated
13:35with each process
13:36this is also called the task control
13:38block or tcb
13:41okay
13:42so for each of the process there
13:46okay so we have what you call a process
13:48control block so pcb which stores the
13:51following types of
13:54process specific information
13:56such as the process state
13:58the process number
13:59the program counter
14:01registers memory limits and the list of
14:04open files
14:05okay so the process state is basically
14:08the running waiting okay so we discussed
14:11in the previous slide
14:13okay
14:14so next would be
14:16the
14:17process number okay
14:20so
14:20the process number is basically the
14:22process id
14:24or the parent process id
14:26you also have the program counter
14:28okay so the program counter
14:30this needs to be saved and restored when
14:33swapping
14:35processes in and out of the cpu
14:37okay the location of
14:40the instruction
14:41next to execute
14:43okay
14:44next would be the cpu registers
14:47okay and
14:48[Music]
14:49that is the contents of all the process
14:51centric registers you've got the cpu
14:53scheduling information also
14:56so this includes the
14:58first in first out in case of the
15:00priorities if it is a round robin and
15:03other cpu scheduling algorithm
15:06all right so next would be the memory
15:08management information
15:10okay so example of this are page tables
15:13or segment tables so we will be
15:15discussing that in the
15:17latter chapter of this uh discussion or
15:20or of this book or of course okay
15:23so next one would be the accounting
15:24information
15:26it is a user and kernel cpu time
15:28consumed okay account numbers limits etc
15:32and the last one would be the i o status
15:34information so the devices allocated
15:37the open file tables etc
15:40okay
15:43next
15:44threads
15:45you have seen threads earlier on our
15:50task manager let me bring up again my
15:52task manager here okay
15:54so you'll see trends here now what is a
15:56trend so chat basically are some
15:58processes
16:00so take note that when you execute a
16:01process when you execute a program okay
16:04making it a process
16:06there are some processes associated with
16:09that main process and we call it trends
16:12okay so a good example of threads are
16:15the sub processes associated with
16:17microsoft word
16:19all right so let me open a microsoft
16:22word all right
16:26so win word let me open it
16:29so you'll see that on the taskbar i have
16:31opened microsoft word okay
16:34and see what happened to the number of
16:36threads here
16:38so it dramatically increases because
16:41inside that process or microsoft word
16:44process
16:45there are some processes there like a
16:47spell checker the grammar check
16:51letter counters word counters etc so
16:54these services are in the form of
16:56threads and we will be talking about
16:58threads
16:59in the next chapter of this presentation
17:03right or in the next chapter of the book
17:05let me close again that
17:07ms word
17:08all right
17:09so so far process has been a single
17:12thread of execution so consider having
17:14multiple program counters per process
17:17so you can have multiple threads of
17:19control
17:21right
17:22so we must have then a storage
17:25for thread details
17:26multiple program counters in
17:29the process control block or pcb
17:31okay again so we have a detailed
17:33discussion of threads on the next
17:36chapter of the course
17:38okay
17:41next so this is a
17:43process representation and linux okay
17:47so we're in the current process
17:50and currently executing processes in
17:52here okay
17:54you've got the stack task
17:56strap process information
17:58okay so this is how processes are
18:00represented in linux and this represents
18:04or represented by the c structure task
18:07strat
18:08okay so we will not be dealing with the
18:11os specific here so we just want to get
18:13into the operating system concepts that
18:16are applicable on any of the operating
18:19systems so well there are some features
18:21here that might be unique with the
18:23specific operating system
18:34[Music]
18:40foreign

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