Soma: /* Notes */

2018-10-11T15:26:25Z

Notes

← Older revision		Revision as of 15:26, 11 October 2018
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	'''Where do processes come from?'''		'''Where do processes come from?'''
	* Can be visualized as a tree hierarchy		* Can be visualized as a tree hierarchy
	* Every process has a parent ~~and a child~~		* Every process has a parent
	* In windows one process specifies the executable of another

R.samanfar: /* Notes */

2018-09-19T17:09:21Z

Notes

← Older revision		Revision as of 17:09, 19 September 2018
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	==Notes==		==Notes==
			'''Where do processes come from?'''
			* Can be visualized as a tree hierarchy
			* Every process has a parent and a child
			* In windows one process specifies the executable of another


			'''Orthogonal Design in API's: Unix Principle'''
			* Only one way of doing an operation
			* Complex operations are made by simple ones


			'''Process Duplication'''

			Cases for making a new process:
			* Run a new program
			* Duplicate an existing process


			'''Why would you think of duplicating a process?'''
			* It's not the same as running a process a second time
			** Variables and state are carried over
			* The duplicate becomes the child and the original is the parent


			'''Process Duplication and Unix'''
			* Useful operation for concurrency
			* Simple interface
			* Can be combined with other operations to run programs


			'''Shell'''

			*These commands make up an important part of the unix shell:
			**Fork: The action to duplicate a process
			**Execve: Replaces the process running with something else
			* Most operations you perform are done by forking the current process and execve to run the commands binary
			* If you don't want to `fork` you can write `exec` in front of your command.
			*The result is your shell morphing into a command. Once your command ends, your terminal will close


			'''Finding documentation from the shell'''
			*$ man 'name of command here'


			'''Running LS from another program'''

			_Execve is a suicide call_
			*in C:
			**argv and envp are params given to main

			execve("bin/ls", argv, evnp);
			printf("Hello");

			*printf will not run since program morphs into ls


			*What if we want hello to print?
			**If you just throw `fork()` in you will lose track of which process is the parent and both duplicates will do the same thing


			'''Fork: The two faced method'''
			* Based on the return value you can identify the parent process:
			* Fork returns the PID of the child to the parent
			* Fork returns 0 to the child


			*In the following scenario, the main process terminates before `ls` runs resulting in the terminal re printing its prompt before `ls` outputs
			**C code example:
			PID = fork();

			if(!PID){
			execve("bin/ls",argv,envp);
			}
			else{
			printf("done");
			return(0);
			}



			*In order to avoid this we need to add a `wait()` so that the parent process waits for its child to terminate before it does.
			**Cxample C code:

			PID = fork();
			if(!PID){
			execve("bin/ls",argv,envp);
			}
			else{
			wait(NULL)
			printf("done");
			return(0);
			}



			'''What happens to a child process when a parent dies?'''
			* Another process becomes the parent

			*Some process status code examples:
			S = Sleeping
			Z = Zombie (A process that died but is still there)

			*If nobody waits for a process that dies it becomes a zombie
			**"If you have a kid, wait for it to die"


			''' What is kill?'''

			* Clicking X on a window is how we normally invoke the kill command.
			** This triggers a signal which is something used for processes to communicate between each other


			* `$ man 7 signal` is the command that shows the list of signals

			examples:
			`kill -STOP PID`
			`kill -CONT PID`


			*Some processes can handle signals differently thanks to signal handlers

			`$ kill -9` can avoid signal handlers and kill mercilessly

			*The `wait()` method responds to `sigchild` which gets the signal of a child dying


			'''About `int main` parameters: '''

			* char* argv[] is an array of strings
			**Each string comes from input separated by whitespace when entering a command

			argc:
			Count of how many strings are in argv

			envp:
			evironment variables(state) was passed in

Soma: Created page with "==Video== Video from the lecture given on September 7, 2018 [https://homeostasis.scs.carleton.ca/~soma/os-2018f/lectures/comp3000-2018f-lec02-20180907.m4a is now available]...."

2018-09-08T18:18:13Z

Created page with "==Video== Video from the lecture given on September 7, 2018 [https://homeostasis.scs.carleton.ca/~soma/os-2018f/lectures/comp3000-2018f-lec02-20180907.m4a is now available]...."

New page

==Video==

Video from the lecture given on September 7, 2018 [https://homeostasis.scs.carleton.ca/~soma/os-2018f/lectures/comp3000-2018f-lec02-20180907.m4a is now available].

==Code==

Code and files from the lecture (captured as they were at the end) are available [https://homeostasis.scs.carleton.ca/~soma/os-2018f/code/lec02/ here].

==Notes==

Operating Systems 2018F Lecture 2 - Revision history

Soma: /* Notes */

R.samanfar: /* Notes */

Soma: Created page with "==Video== Video from the lecture given on September 7, 2018 [https://homeostasis.scs.carleton.ca/~soma/os-2018f/lectures/comp3000-2018f-lec02-20180907.m4a is now available]...."